01 Honda CR125r | OEM except No Base Gasket - .030

I just did some research on mixxxing nitro-methane with gasoline. Long story short don't do it. They won't mix right without other additives. Nitro-methane goes best with alcohol in a motor designed for it both fuels.

I am thinking I am gonna grab a couple gallons of various racing fuel octane level & some straight pump gas for messing with. I will slowly up the octane level in the fuel gallon by gallon when I am at the track to see how things go. No sense in blowing the motor straight away. May as well get a few laps out of it first. Hahahaha.

If I need parts, will let you know.

+1 to everything summarized about nitro methane by project racer. I gleaned similar from researching the net & it all rings true. project racer did well in summarizing quickly what burning nitromethane is all about & what it takes to run it much better then many forum posts out there. In short project racer is right, CH3NO2 is a world apart from C8H18.

Nitromethane I just tossed into this thread on a whim as I was already rambling about fuel. This CR I am screwing with will more then likely never see nitro methane, if its lucky. I have a KX500 I may build to run a little nitromethane though because obviously a nitromethane burning KX500 is a good idea worth exploring. Hahahahaha!

Actually where I am seriously at with nitromethane & my KX is I am looking into using it as an additive for high elevation riding. I live in Denver, CO, ride MX at 5280 feet and ride trail between 8000 & 12000 feet average with peak elevation between 13,000 & 14,000 feet. Since Nitromethane increases compression while while burning with less oxygen I am wondering if somehow it could be added to gasoline in small quantities to boost power at high elevation.

For all the lowlanders out there wondering why screw with dangerous fuels that bring O2 and deliver compression take a look at the below pic. The red box indicates where I trail ride elevation wise. Note the high elevation has 25-40% less air density then in the low lands of the common world. The higher a ride goes up the less air there is, the less O2 there is & along with it the less compression an engine makes per gulp of air while burning poorly due to lack of O2.

Thanks ahead of time. I have heard av gas was a good route. Its on my list of fuels to try.

I took the CR out to the track today & kicked the crap out of it. Everything went well except the copper spray gasket blew out after about 30 minutes & began leaking. This comes as no surprise really as that type of spray gasket is not designed to be used as a standalone cylinder base gasket. The base of the cylinder wasn't leaking that much so I brapped on for a few more hours & had a good time of it. I tried out three fuels today with a mixed bag of results. Here is the scoop:

Basic Super Pump Gas / 91 Octane / 10% Ethanol - Ran Good, Pinged

Unknown Fuel / 100 Octane / No Ethanol - Ran slightly better, Pinged about the same as the Basic Super Gas with ethanol, Not much performance benefit, Overall the bike felt crisper is how I would describe it.

Sunoco 110 / No Ethanol - Braaaaaaaaaaap! Ran great, Best power, Substantial boost to mid range, got onto the pipe faster, hit harder once on the pipe, Best value for the $$$ at $10 a gal. compared to the 100 octane fuel.

The basic super pump 91 octane gas I got at a Shell station. The 100 octane no name fuel I got at a Conoco that probably doesn't sell that much of it. The 110 octane I got at the track. The 100 octane I think was old. The station doesn't seem to sell much of it is my guess. The person working there knew nothing about it other then, “100 octane. Don't put it in you car.” I didn't know the track sold fuel otherwise I would have picked up 100 octane there along with the 110 octane I did get there. For the money the 100 octane was worthless. $10 a gallon of 100 octane got me a crisper feeling bike. $10 a gallon 110 octane got me a slammin' bike, a huge grin and a penchant for moar 110 octane.

For the money don't waste cash on 100 octane is where I am at especially if the plan is to mix it with other fuel to spread it out. I am not completely giving up on 100 octane. I will try some at the track since I know its there now. It may show better results if fresher is my guess. At the same price roughly as 110 I don't see the point though really.

To cut to the chase on the 110 octane let me just say its the fuel that puts the “F” in “Fun”. Jeez it ripped hard. If I had money to burn, literally, I would burn nothing but 110 octane in all my bikes, cars & lawn equipment. Once on the pipe, heck even gettin' on the pipe, 110 octane just straight up ripped. Every time I hit the gas it was like, SKONK! that crackly resonating noise that just emanates from a good running 2T.

As for the copper spray gasket blowing out its no biggie and was expected. I am tossing around whether to try yamabond next or just slip a thinner then OEM gasket in & call it good. I already have a set of 5 base gasket measuring .0015 , .005 , .010 , .015 & .020. I am leaning towards a .0015 base gasket slathered in Permatex High Tack next. I have only read rumors on yamabond working as a base gasket. Maybe it would work or maybe it would blow out in a few hours. Below are pics of the blown copper spray gasket. I will be tearing the top end off soon & will post pics back of what I find.

After getting the top end back on with a decent seal on the base of the cylinder I will do some moar fuel shopping. Next on my list is basic super 91-93 octane without ethanol & also some AV gas. I need to find a place to get the AV gas though. I am not sure about rolling up to Denver International Airport & looking for AV gas. That airport is far away, too big for comfort plus that freaking DIA devil horse is just weird & freaks me out. Hahahaha!

Of course the bike is all dirty now that it needs pulled apart.



The copper spray gasket blew out on the front, back & sides. Here are pics of the sides.





.0015 , .005 , .010 , .015 & .020. base gaskets



DEVIL HORSE guarding the AV gas at DIA. True story.

Propane is a great idea. Snowmobiles have messed with injection systems I read some where. Thumb button propane injector would be nice for climbing passes.

I read about some chainsaw tuners going down to .020 with good results with their saws. They were using Yamabond as a base gasket material. After reading that & some other 2T moto threads about Yamabond 4 as base gasket I decided to go gasketless with Yamabond. May as well try things right with an actual fuel resistant gasket maker on the base of the cylinder.

Tear down should the piston & head looking good. The top end went back together with Yamabond 4 this time. Looking to this weekend to try some moar fuels.

I haven't torqued the nuts yet. I hand ran the nuts down to level the cylinder with a tight clearance. I cleaned the excess off when it was still wet & leveled best I could by eye while keeping nuts loose. Its been 4 hours now at around 68 degrees F. May wait till tomorrow to tighten nuts. With so thin a layer I would like to be sure it is solid. Had to be thin though for tight squish. Base nuts are 20lbs so light torque. Will probably blue locktite em shy of 20. Here is current clean pics before base nut torquing. Head to frame mount is still loose too.

Close up of the Yamabond layer in left rear base nut area before torque.

First time building an engine? This - > "bro buy a gasket set"

Built a few engines and want to mess around for fun? or cheapskate? This - > cardboard, tag board, construction paper, actual bulk gasket material in specific thicknesses, soda cans, beer cans, sheets of aluminum of specific thickness, sheets of copper of specific thicknesses & many other types of materials can all be used for custom gaskets. Old gaskets can be reused too. Regardless of the material a liquid gasket sealer of some type should be applied to the material after the gasket is cut & before install. The sealer should also be applied to the surfaces being sealed together. It the material is paper/cardboard then Indian Head Shellac is best used if the seal needs to be hard/rigid or High Tack if the seal needs to be soft, tacky & flexible. If aluminum or copper material is to be used then high temp BBQ black copper, or silver spray paint can be used to seal/reseal the gasket if moving heat is a consideration in where the gasket is going. If heat &/or heat transfer is less an issue & just a good seal is wanted High Tack goes well with aluminum & copper gaskets too. Here is Permatex's line up of gasket sealant products. http://www.permatex.com/products-2/product-categories/gasketing/gasket-… See above pics of intake boot / reed valve / engine joint for example of reusing gaskets & seals with Permatex High Tack gasket sealant.

All ready done the above? Looking for something else to try? This - > Various gaskets can be replaced with various types of soft, semi liquid, or rigid gasket makers. Examples of such gasket makers include RTV blue, black, grey, red ect. ect. Various types of joints will need gasket makers designed for the use to the specifications of the joint. Be sure to pick the right type of sealant. Rigid vs soft, temperature rating & fuel / oil / antifreeze / ect. resistance are all factors in choosing the right gasket maker to replace a gasket. Permatex has pretty much all types of gasket makers available in their line up. http://www.permatex.com/products/product-categories/gasketing Their are countless equivalent products available fine tuned for various applications such as Yamabond 4 (made by 3Bond) is a product equivalent to Permatex MotoSeal 1 Ultimate Gasket Maker Grey. See above pics of power valve cover for an example of Permatex Black RTV used in place of upper power valve paper gasket and for refurbishing & sealing the old beat power valve bottom rubber seal.

Yamabond 4 https://www.rockymountainatvmc.com/p/941/2854/Yamalube-Yamabond-4

Permatex MotoSeal 1 Ultimate Gasket Maker Grey http://www.permatex.com/products-2/product-categories/gasketing/special…

One thing to note in this is to not confuse gasket "sealants" with gasket "makers." For instance spray copper is a gasket sealant made to seal a gasket between surfaces. Yamabond 4 is a gasket maker designed to be a standalone gasket between surfaces. Gasket "makers" don't always work well if used as gasket sealants. Gasket sealants don't work well as gasket makers. Case in point the spray copper didn't last long on CR cylinder above when it was used as a stand alone gasket. The copper sealant blowing out also had to do with the copper sealant not being very fuel resistant. Copper spray gasket will work in fuel resistant capacity only if it is applied to a gasket sandwiched tightly between surfaces, for instance the used head gasket sealed with copper spay on this CR125 which is working as it should because the copper spray is being used as it was designed to be, with a gasket. Yamabond 4 replacing the base gasket is as proper of a gasket maker choice as it gets for such an application. Yamabond 4 is a flexible, high torque, heat / fuel / oil / vibration resistant gasket maker that should do well as a base gasket. Many 2T engines have been built with Yamabond 4 as a base gasket. Search the web for more info. Whether or not Yamabond holds in such an application depends on several factors including how clean the surfaces were when the Yamabond was placed, how thick the layer is, the thickness after torque and whether or not the gasket maker is allowed to cure properly before use.

Torqued the squish is up to .033". The sealant is probably around .003" thick when torqued. Run time will tell if that is thick enough for the Yamabond to hold. Thin as it is there definitely was a cushion of sealant I tightened the cylinder into so that is a plus. Gonna let it cure for few days before firing the bike up.

Already back together & waiting for the next day at the track.

I took the bike out to the track again. The Yamabond 4 was a success. It is holding good. I tried a 91 octane ethanol free gas this time. It really performed great. I am not sure why but the 91 no ethanol performed as good as if not better then the 100 fuel I tried last time. I am leaning towards freshness of fuel, quality of refinement & additives come together to create performance of a particular fuel in addition to octane rating.

I plan on doing more experimenting with fuels when warmer temperatures return in the spring. Its hard to gauge performance of a fuel with a 120 degree cylinder head. Yesterday at the track a storm front was coming in with the daily high in the upper 40s. I actually had to cardboard off my bike's radiators to keep a consistent head temp. between 150 - 160 degrees. Even with the cardboard the head never got above 160 degrees.

Jetting will also come into play to find best fuel performance as well. With temps so low though messing with jetting is kind of a lost cause though as everything will change when daily high temps reach into the 80s changing fuel characteristics.