RMZ250 AX Team Build (with old JGR & BarX parts)

Wheels

We start with tires from Maxxis, they’re new to the program. I’ve been really enjoying these new tread patterns, they seem to grip like the dunlops, but last a good bit longer. I had previously tried the Maxxis tires that come stock on the gasgas bikes, and seem like a harder compound version of the Pirelli’s. The tires I just purchased though are the newer MX-SI tires, and they seem to be their own tread pattern. I’ll give more feedback once I’ve worn out a set, but so far I like them quite a bit and haven’t had any frustrating knobby chucking or washing out. The pic below is from the AX season, when we were stilll buying Dunlops.

The rims are D.I.D. Yellow dirt star ST-X rims, mated to OEM hubs or sometimes Tusk hubs with the gold anodizing stripped off. 

Brake discs are either OEM or Pro-X, you’ll find a lot of pro-x parts on these team bikes when I need an oem level replacement. I use them for gasket kits, suspension seals, chassis bearings, timing chains and all sorts of odds and ends. 

Dirt Tricks and D.I.D. Chain are putting the power to the wheels. Seriously, Dirt Tricks sprockets are CRIMINALLY UNDERRATED.  I haven't had to replace a single sprocket.

Engine 

I used to get the engine as a sticking point when talking to riders, typicallly they hadn’t ridden an rmz. Frankly, it gets a worse wrap than it deserves. The dyno sheet below is pulled directly from the dirt rider shootout using PC’s dyno. I love referencing this, because it not only shows the RMZ strong from low rpm to middle, but the golden goose of shootouts is grossly overhyped according to the actual numbers.  

So that being said, my goal is to accomplish three things:

-Keep the reliability 

-Improve the overrev to compete with Austrian stuff

-Improve the bottom to mid to have the best 250 in AX in that rpm range. I genuinely believe that’s attainable. 

Ok, I went overboard with buying old JGR stuff…what started with a couple sets of cams for the 2024 season turned into a mad dash to buy anything I could.  I have 4 works heads, 18 different cams, a complete works bottom end, and a couple works throttle bodies. Here’s the rundown of what’s in the motor:

Works transmission. Most ratios are the same, but you won’t find neutral and 2nd seems longer. 

Hinson clutch. They have different primary gears available to change the gearing internally without changing the rear sprocket and subsequently swingarm length. For the sake of keeping it simple though, we’re using standard primary gears. 

Different inertia flywheels. Lighter isn’t always better, I hate the lighter ones in whoops and in loose soil, it revs past the sweet spot too quick. Doc likes the 6.0 inertia (6.2 is stock, 5.7 is stock for a 450 or older 250, and jgr has even lighter and heavier ones available)

Works cases with a different oil sump beneath the crank. I believe it was to reduce windage and lower center of gravity. I believe they had another works version to supply more oil pressure to a plain bearing rod, but I wasn’t ready to deal with increasing the oil pressure and sourcing different crank seals to handle that. 

Custom 1.5mm longer rod, DLC coated to shed oil I assume? Kind of surprised the pin area isn’t dlc, but the oem wrist pin is so maybe they don’t put dlc surfaces against each other. 

Custom JE piston, around 15:1 compression

Piston has gas ports, and baker would radius every sharp edge as well as put some cross hatching on the skirts (I assume to relieve stress risers and  for oil retention)

It uses the stock ring pack and wrist pin, although the pin is offset 1.5mm higher to accommodate the rod. 

+1mm intake and exhaust valves. 

They honestly look just like oem valves, just 1mm larger diameter. Sorry if you were expecting trick looking pieces here. 

Works head

Ported, with epoxy added, intake floors raised, and intake length 5mm shorter. 

Works material valve seats

Combustion chamber polished and machined for flame travel and to match the piston profile

The heads were decked between .2 to .4mm depending on the intended use. Squish clearances were documented, and the amount decked is logged in the build sheets and engraved on the head.

NGK spark plug, I don’t know what’s special about it, I just know when you google the number on the side of it you can buy one for $80, so I assume it uses unicorn horn as the porcelain. 

Works valve springs, with installed height carefully set to achieve target spring pressure for the necessary cams. I have mine set to handle the most aggressive cams I have data for so we can swap out to try some different profiles without risk. This has been an area Dean has taught me a ton on, and I know I’m only scratching the surface. 

Retainers, keepers, and shim buckets are all works as well. 

The retainers are steel and machined to keep the weight down. 

The valve locks are titanium, which makes putting them in slightly tougher as you can’t use a magnet to hold them in place and they like to bounce around as my spring compressor is going down. 

The shim buckets are DLC coated. I don’t know if there’s any other magic in these, that’s just what sticks out at me. 

TiLUBE supplies the oil, and to their credit we went all season on the same clutch packs this season, with a switch to their full synthetic. Last season I had riders request mineral oil, one even requested Rotella, and they generated more heat in the clutch. Nobody complained about the clutch feel when I quietly switched everyone to the synthetic. 

TiLUBE also has a fuel line, TiFUEL. Since the AMA  doesn’t have fuel testing in AX, we run their TF4U fuel. Joe, the owner, has it blended by Renegade to his own specs. They have a better performing fuel comparable to Pro6, but if it costs $180/5 gallons to have a 6% gain, and $100/5 gallons for a 5% gain, I’m going to take the 5% gain as the diminishing rate of return just isn’t worth it at this level. We tested this fuel, fuel factory, ETS, and VP. We had consistent results from can to can with the TiFUEL, something we struggled with in years past. This fuel wins in the dollar per horsepower ratio, by a lot, and is as consistent as anything else I’ve found.

Little stuff, I know I’m probably overlooking a million little details. For example, I’m pretty sure the dowel pins were kashima coated or hard anodized because they were brown and slid out like butter on hot pancakes.

The porting was very interesting, as I measured certain dimensions on each head I purchased, and had done the same thing to some other heads I have come across in the past. I tried to measure depth of the divider, choke point height/width/cross section area, and the same at the throat. Most customer spec heads follow similar ratios, and one I refurbished was completely hogged out and ran like crap (from a BIG name engine builder too I might add).

I know there’s a million other factors to porting, but more importantly I know I don’t know $#!%. Most of those heads have a choke point on the intake before the short side radius of 68-72%, and even one of the more radical JGR heads I have (with an epoxy fin before the guide to divert around it) maintains the cross sectional area by raising the roof on either side of the fin.  

I’ve tried doing similar epoxy work on a production based head, and it’ll go on a practice motor for the team.  I was surprised how well a scotchbrite dremel wheel works at shaping the epoxy.  All of the heads with epoxy appear to be finished with a fine scotchbrite wheel, as they’re lightly polished vs the normal burr or 60 grit finish.  The epoxy is either splashzone, or Goodson’s PRK99 (port reshaping kit). I used Goodson’s for my spare head.

(aforementioned trick dowel pins)

Head build sheet with spring set length formula, max rpm, spring force requirements, and probably more data I’m overlooking. 

Cams

There’s so many cam options, I’m splitting this into its own category from the engine stuff. Firstly, there’s three sources of the works cams that I have, webcam, Yoshimura, and Suzuki Japan. 

Dean’s go to preference is usually a webcam combo, and I have 7 of these intake cams, and 3 of these exhaust cams. I also have a shorter duration exhaust from web, and MASSIVE lift intake from web (it’s actually the same grind number they often used on the 450’s). 

For the yosh cams, I believe I just have several of the exhaust cams. They appear to have slightly less lift, but longer duration, requiring a bit more spring tension and according to the online calculator I found, slightly more lobe area than the higher lift webcam. My theory is if I use this exhaust with my normal intake I may see a bit more top end. There is also one MASSIVE lift exhaust from Yosh labeled HY-04, that I assume was paired with the 45 grind from webcams on the intake, but I don’t know, so for now those two will probably sit on the shelf (.415” and .377” lift, vs our usual .380 & .360”). I don’t have any spec sheets on that big exhaust, so I need to grab a dial indicator to try to find duration at .05” to make a comparison. Holding it up to an HY06 it appears to have a similar ramp, but shorter duration. I almost wonder if it has the same or similar lobe area as the HY06. 

Works Suzuki cams: I think I only have one, an intake with a strange marking. In measuring the base circle and lobe it appears to be .370” lift, on par with some Yoshimura intakes and even some hotcam options, but I don’t know the duration. I do know the lobe center was DEFINITELY timed for top end. I have documentation that this was paired with one of my Yosh exhaust cams and ran in one of my works heads for an Alex Martin practice motor.  

The required spring force to keep these from self destructing is calculated using the max rpm, lift at highest valve acceleration (not max lift like I would have thought), and valvetrain weight. I don’t know the formula, I just know the needed numbers that Dean provided for some of the cams I have. As a result, I can err on the side of caution and set all my heads up to have the needed tension for the most aggressive cams, and try different combos to maybe find a riders preference for AX. Pictured below is a build sheet with some of the variables to calculate your set spring height. I built a spreadsheet to help calculate this and determine the needed spring shims. 

I also built a spreadsheet of various cams to try to form some sort of theory on what effect each cam combo would have before I start testing. I used an online calculator to determine the lift area, to see how the different profiles stacked up with their different lifts and durations. Since I have so many of Dean’s preferred intakes, I’ll use them as the constant, and change the exhaust cams. My theory is the shorter duration, same lift profile will give more bottom end, and the slightly smaller lift, longer duration (with larger total area) will yield more over rev.  At some point I will also try the A Mart practice spec combo as well, as my assumption is that is set up for the most over rev based on the higher lobe separation angle and the ratio of intake to exhaust lift area. I don’t know if I’m going to try the cams with the significantly higher lift (Web 45/HY04 Yosh) as I simply don’t have any data on the spring force or RPM restrictions, and the intake is .025” higher lift, and the exhaust is .017 higher than anything I have the force requirements for. Pretty substantial jump. 

Intake

We have these cool filter cages that give more volume, thanks to a 3d printed extension. Towards the end of the jgr Suzuki team they found extra power by creating a tunnel from the rear fender channels, through the seat support, to the filter. I did have to re-route the electric pump battery, but that’s worth it. I'll try to get some good pics soon of the seat mods for the airbox.

DT1 supplies the filters, and they hold up very well after several seasons of cleaning with diesel or bio-degradable options. 

Once it gets to the throttle body, we have a works version. A trick lightweight bracket for the electronics and the machining on the engine side and flange welded on the filter side are the most noticeable aspects. This with the head flange machined another 5mm, move the injector and butterfly 10mm towards the engine. 

I noticed that too!  A few weeks prior to that pulp show, I got an old race sheet from JGR with all sorts of notes.  I was scanning through it to see if there was anything attainable to me and noticed the seat was mentioned (highlighted below).  It was on the backburner for a while, and then A Mart was raving about it on Pulp, so I asked Dean what the heck he was talking about.  I tried to get some cell phone pics of how I cut it, but basically they take a chunk out of the back of the seat (directly above the channel molded into the rear fender) and then drill holes in the plastic seat base where it sits on the subframe cross member.

HP Race Development has a good YouTube video of dynoing the RM-Z250 with some airbox mods that show some big gains from getting more air to it as well. Seems to be an easy power grab.

Thank you!  As for the looks, I really can't thank Ryan at Throttle Syndicate enough.  I know we're not even a fly on the elephant's butt that is pro race teams, but he doesn't hesitate when I throw out an idea to run and treats us like absolute royalty.  As an added bonus, he's a fellow RM Army member so we bounce a lot of ideas for the 450 off of each other!

I have only ridden the works motor in the parking lot at Oak Hill😂, but I'll try to get some time on one myself soon.  That motor feels drastically different despite on paper it looking similar.  

I've been racing an Arkansas series on Cody Groves' race motor from last season.  It is basically a customer spec JGR head, but instead of the JGR engraving has a Baker Speed sticker as it was done in Dean's personal shop.  It has great bottom to mid for a 250, then starts to fall flat right around what feels like 12-13k RPM, then seems to kick in to over drive to the last little bit.  I've only ever felt that sensation in 16-21 KTM group 250's, so that's pretty cool.  I currently weigh 240 lbs (dad bod kicked in and I ate my feelings the last few years) and am 6'5", but I've holeshot half the motos I've raced on it in the little Arkansas series I've been going to.

So from what I gather they typically stuck with the same cams.  Here's what was in A Mart's bike in Red Bud 2020, as well as some other build sheets I can dig up:

That said, the HY06 Yosh exhaust cam they paired with a works Suzuki intake does have 250 degrees of duration.  I have a few of those to try.  They are a little less lift, but with the longer duration I think they are around 99.3% total lift area of the intake, vs. 98.6% lift area of the Webcam 297 cam we usually run.  

I appreciate you commenting, because I'm essentially a monkey with a loaded gun over here.  I have access to the internet, and a few books, so I have theories, but not necessarily knowledge.  Thankfully though, Dean Baker did tell me what spring pressure I needed to safely run these cams, so sometime this summer my plan is to do a little exhaust cam shootout, and grab a dial indicator to measure and graph the lift at lobe centers and 5 degree intervals to compare the following:

-Web 297 (our baseline setup)

-Web 1213 (same lift, shorter duration exhaust)

-Yosh HY06 (.010" less lift, bigger overall area though)

With Doc Smith healthy now, and Branden Walther interested in racing AX next season, I have two quick guys in my area to try these back to back when we get a weekend to do so.  The cams and the electric water pump are the two big items I want to get feedback on (and temp data for the water pump).

Speaking of testing, we did a little back to back with the cut seat base on the JGR customer spec motor with Branden this weekend.  It filled in the dead spot right before the over-rev that I had previously described.  Kudos to the JGR guys for finding that, because it was a $0, 10 minute mod that yielded a noticeable result according to the butt dyno.

Great minds think alike.

-I bought a 12 volt rechargeable lithium battery from Amazon. I’ll check the amperage when I get around to doing the write up on the pump. I built a wiring harness for it with a switch and plugs initially designed for mounting LED light bars on motorcycles so I’d have a handlebar switch that lights up red when it’s on. My initial plan was to buy a furukawa two pin connector and use the femal end on the OEM wiring harness to power the pump. I had that built over Christmas time, and then Myron Short at BarX told me they fried stators running it that way, so I bought the battery packs lol. 

-I set the spring tension in all of my heads to handle the most aggressive cams and 14,250 rpm using the recommended spring force from Dean and JGR. 

-that’s good to know about all the coatings! Paul at jgr told me a lot of parts became “works” after the oem part received whatever coating or processing they did for hardness, friction reduction, and overall reliability. There seems to be a few codes after a standard part number for works stuff, that typically correlates to the source. Things like US3 cases, GP_, XR_, etc. 

I’ll try to look into some more of these coatings, as I’d like to be able to duplicate some of what’s in these!

You certainly could send out production parts to get coated, and honestly I don’t blame you if that doesn’t constitute “works” in your eyes, I was just relaying some info from the JGR guys as to what some of what they did was. 

Frankly, a lot of “works” stuff isn’t that glamorous. The oversized valves for instance, they look identical to OEM ones, just 1mm larger head. Same with the cases, if you didn’t know what they did with the sump area at the bottom it would look identical to a production set. 

I’m in the middle of moving houses this month, and hopefully will get situated and more detailed pics once everything is moved over. Sorry for stalling on this thread!

I’ve been using Fastlap Suspension out of Alabama. He’s come up with great settings for my outdoor stuff on both the 250 KYB and the 450 with the BFRC rear shock. I even have a Frankenstein set of old psf2 forks and BFRC shock to be able to throw an mx set on a bike so I can race locally on one if need be, and he’s even got good settings for those. He’s done the best at accommodating for my height (I’m 6’5”), which makes it tough to get suspension to hold up enough as I tend to either be too far back, or occasionally too far forward. 

I leave it up to the riders in AX if they want to use their own tuner, or use Fastlap. This year Doc Smith and Josh Carson had settings by Fastlap, although they preferred pretty different setups. By the end of the season, josh was requesting something stiffer like what Doc had. 

PR2 has done Cody Groves when riding our bike, and Core MX did a set of mx stuff on the 450 using stock showa components, and a KYB indoor set for Jake Masterpool before his back was hurt. I haven’t ridden any of those indoor setups, but can say Core did a good job with the 450 Showa stuff as well. 

Man, no kidding! 

Whispern reached out to the teams instagram and wound up buying his own RMZ from his local dealer using the RM Army program. I can’t take credit for anything, I’ve just told him what parts we use and wanted to help boost some exposure for a good kid on the team’s page. He’s an awesome kid, and has a very level-headed dad, so it was great to see him put it in the motos at Colorado in his first attempt! 

He and his dad are waiting to see the AX schedules for 2026. If the AMA series has us all over the US again, they’ll probably put together their own program to race the GT series as it’s all so close to them in Oklahoma, unless I can come up with some sponsors to help with their travel. I’d love to put them on the team for next year, and the offer is on the table if he can get into futures (or SMX next, or whatever they call it next year) to borrow a race 250. 

I have measurements in both, just as a result of pulling data from different sources. JGR, Yosh, and Hotcams all document their specs in millimeters, but webcam (the source of JGR cams), and most valve spring manufacturers provide the data in inches, so I just do a lot of conversions in my spreadsheets to make sure the spring requirements are met. Thankfully millimeters to inches is a big enough difference you don’t really get them mixed up (approximately 25.4mm =1 in). 

JGR documented everything in millimeters. Assembled spring height, cylinder height, cylinder head height, cam lift, lift at max valve velocity, etc. 

Located just north of Dallas in Aubrey, although closing on a house this month in Valley View a little further north of DFW. 

Finally got moved into the new house, with more garage space! I tore Doc’s race bike down to the frame and started rebuilding and inspecting parts. Here’s how it sits now, and how the piston looked after 15 hours running TiFUEL and TiLUBE. It looks like either I’m running a little rich (based on what I’m assuming is the fuel washing the piston) or it burns miraculously clean. Either way, it ran amazing with no bogs, so I’m hesitant to change. 

If you’re ever in the Dallas area, let me know if you want to take one for a spin. I live pretty close to oak hill and Masterpool’s. I think the series is doing round one on the west coast, but with the travel schedule I only attend the nearby rounds in person. 

As for the flywheels, I think it was a Mitch Payton quote that sticks out in my mind every time the subject comes up, “kick a balloon and kick a soccer ball and see which one goes further”. 

Some updates now that AX is done. Our 2026 setup looked AMAZING once again thanks to Throttle Syndicate.  I have a few ideas rolling around my brain for next year, I think we'll be able to keep the tradition of beautiful RMZ's rolling into next year.

My 250 with a complete JGR works engine is on loan right now for supercross, and I’m going back through the other 250’s as well as studying a 2023 (or at least that’s what was stamped on it) BarX motor that was blown up and included in the sale of the remaining BarX suzuki inventory.  I did a little horse trading with some other parts to get my hands on that motor (with a good bottom end), and I must say the gentleman who purchased the BarX stuff is an awesome guy.  One of my riders from this season of AX, Luke Dickey, purchased a 250 from him, as did another friend of Luke’s, and Jim went above and beyond to make sure everything went smoothly.

When I tore the BarX engine down  I was eager to see any obvious differences as well as what failed. They pulled the cams from this engine, the rest was all there.

Head 

-The head was decked approximately .4mm, same as several of the JGR heads I have. 

-Cylinder was not decked. 

-OEM thickness gaskets were used. 

-Throat dimensions on both intake and exhaust were kept very close to OEM. (Roughly 88% of valve diameter). The last time I measured a twisted head was a 2016 yz250f, and the bowls and throats were hogged out to over 90%. 

-The valve guides were all cut flush with the roof of the ports. I know there’s formulas to calculate if a shorter length can support your valvetrain/cam/rpm combo, but frankly I don’t know it and thus I’ve always been scared to grind them down. 

-They ran +1mm valves, similar to JGR, but appear to have sourced them from someone other than works Suzuki.  There’s no branding on the valves, but Twisted and BarX’s relationship with Race Winning Brands makes me wonder if they were custom ordered from their valve company, Victory 1 Performance.  Purely a guess, but that’s who’s been making titanium valves for ProX lately too as they try to keep it in the family amongst the race winning brands.

-Where JGR shortened the distance from injector to valve (5mm off the flange, 5mm off the throttle body, filled in the long side radius of the ports and raised the floor) this head seems to inadvertently lengthen the intake tract.  No shortening of the intake flange, and there is a nice bump of epoxy on the floor of the intake.  I grabbed some measuring tools and jotted down the cross sectional area and calculated the percentage relative to the intake valve.  No surprise, it follows a common formula known to work in things like sport bikes.

-The combustion chamber is machined smooth with no sharp edges.

A look at the epoxy work on the floor. 

A Baker head by comparison, with the epoxy on the roof above the seat while the floor was welded vs epoxied (I honestly thought the floor would be harder to weld than the roof, but 🤷‍♂️). You can also see where the intake flange is machined 5mm down. 

Pistons

I broke out the digital calipers, and as many old order sheets from JE as I could find in my notebook to make a spreadsheet to compare specs.  For the sake of comparing total dome height, I factored in 1.5mm for the longer rod piston.  The Bar X piston appears very similar to the JGR V4 piston, just with the wrist pin moved back 1.5mm down.  There are other differences, like the slightly taller dome, the lower deck, and deeper valve pockets, but at first glance the profile looks very similar.

Next up is to bolt a cylinder back on and grab a head off the shelf and steal some of my toddler’s PlayDoh to get some squish and piston to valve clearances.  With the off the shelf pistons from JE being at least 1.85mm & 2.56mm taller (and of course I only have the taller of the two on hand) on the dome I want to make sure there’s adequate clearance or see if I need to double up on base gaskets or just break down and custom order a piston.  Thankfully the deck height (second row down) is lower, so hopefully it will clear but just be less ideal for flame travel as the trend I’m noticing is high end builds having as flat of a profile as possible. 

From left to right: Bar X, JGR works (x2), JGR customer spec, (bottom right) 14.5:1 shelf piston from JE. 

Cams

I’ve collected as much data as is available on different supplier’s websites, but honestly I’ve learned that is really only scratching the surface.  I was always under the impression you selected springs based on the max lift, but Dean taught me it’s really the maximum valve velocity. So let’s say you have 9mm of lift on your cam, but when you graph the lift and timing (lift on Y, timing on X) the steepest point on the curve occurs at 6mm of lift, that’s where you need the most spring pressure.  Dean has provided me the needed spring pressures for the cams I have from JGR, but I have no idea what pressures are needed and at what lifts for any of the cams BarX ran.  The guy who bought all the BarX stuff listed off several different grinds and part numbers, and this is what Web came back with for me.

The 100/1213 is sorta similar to Dean’s favorite, as the lifts are identical or near it, but the BarX intake has more duration, and the exhaust has less.  I actually have a few of the 1213 exhaust cams on hand from JGR, so at least I know what spring pressure is safe to use there.  I'm going to build a spare JGR head that I needed valves for (I got some from the same guy who had the BarX stuff) and assemble the valvetrain tonight now that I've gotten measurements on valve protrusions for my spring calculator below:

Bottom End 

I expected a long rod (1.5mm longer like jgr, or 2mm like Carrillo and makes or is common in yz250f builds), but noticed as I looked at the piston there was a normal amount of space between the pin hole and oil ring land. Sure enough, the part number on the rod is for a wiseco Racer Elite rod for a YZ250F (they share dimensions with the Suzuki, so they’re interchangeable). I know that team had used plain bearing rods, but I’m unsure if this one is. The part number in the catalog for the plain bearing rod has “pb” on the end, but maybe it uses the normal rod with just a bearing swap. Either way, no biggie, as I hear the plain bearing has a bit shorter life on converted bikes as it’s tough to generate enough oil pressure. I’ll run 15w50 oil just to be safe, and frankly the RMZ clutch seems to like it anyway.  My JGR bottom end has a similar Racer Elite rod, with the normal RMZ250 part number, followed by “+1.5” to indicate the 94mm length.

-The now infamous electric water pump, and a nice fancy plug in the primary cover.  Their aluminum plug certainly beats my jb weld filled seal to accomplish this lol.

-Every piece in the bottom end seems to have received some sort of polishing treatment.  A lot of the JGR botom end I have is polished, but some stuff has different coatings I’m not at all familiar with.  This thing just is shiny everywhere, even the crank wheels.

Shoutout to @ML512 for pit bits. Because of pit bits I was able to find a part number PAD058 12V Bosch on a water pump and track them down to build my own. That was a couple years ago, and I always wondered if I ran the same pump as the teams or I just stumbled upon another that sorta works… nope, same exact one. Although Twisted 3d printed a really nice pump cover to better fit in the frame and has a mounting support. I did learn from all this though, that they’ve been running a higher discharge rate battery, so I’ll be getting some headed this way shortly. Thankfully I haven’t done any damage to the bike I’d been testing the pump on running a lesser battery. 

The Damage

Both intake valves hit the piston, and then debris caused an exhaust valve to bend. Removing the junk valves took some effort, but it was doable. Two guides and two seats are damaged.  I’ll buff smooth the combustion chamber damage, and once I get seats installed I’ll fill in the gouge in the intake port with some epoxy. I’m wondering what caused the issue. For both intakes to hit the piston, I’m wondering if the intake cam jumped time.  I would consider a part failure if just one hit, but there were clear markings from both making contact. The bike had a manual timing chain tensioner, and I may measure it’s installed length and compare it to the length one of my standard automatic ones extends to under normal conditions.  My only other thought is maybe the cams they were running had more valve velocity and the spring setup couldn’t keep up, but that’s purely a guess.  I do know they were having issues keeping bikes together initially running 15k RPM, and they lowered the RPM limits to 13,500 and got rid of the issues.  JGR would run 14,250, but had the data and testing methods to ensure that was a safe RPM for a given valvetrain combo and spring force. 

I plan on sending the damaged head off to Baker Speed when I save up some funds to have him try to salvage this with some fresh seats and guides.  I will strongly recommend Baker Speed for any of your engine work.  I’m an idiot who just loves to research these things, and Dean straightens me out when I have a stupid idea and is the most reasonable I’ve found on pricing ever.  Seriously, I can’t have a local shop do seat and guide work for what I can pay the guy who’s built factory bikes for over two decades, it blows my mind.