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5405
Joined
10/1/2013
Location
Davis, CA
US
Edited Date/Time
2/4/2019 8:27am
Hey guys, just wondering if anyone has seen this before. Bike is a 2011 YZ450F with a 470 kit and GYTR head (full kit with head, valves, cams, etc.). From my notes these cams have been in the bike for about 19 hours and came with the new head, but there seems to be a lot of wear already. This bike has seen nothing but full synthetic oil since the head was put on and it has been changed regularly. Bike is also always warmed up properly prior to riding, so I don’t think this related to improper warm-up. Also of note, this was discovered when checking the valves and all of my clearances are LOOSER than spec, rather than tighter like you would expect.
Am I hosed on these cams or are they still alright to run? I have a hard time understanding why I’m getting wear like this, seems very odd to me.
Am I hosed on these cams or are they still alright to run? I have a hard time understanding why I’m getting wear like this, seems very odd to me.
from the photo it looks to me like possibly crappy cam material or insufficient hardness or insufficient depth of heat treating etc.
it also looks like some of the journals are lightly scored. can you feel any light scoring on any of the journals with your fingernail?
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Barnett, I’m using mobile 1 full synthetic, changed at least every few hours along with filter. I was wondering about the heat treating as well, it’s almost like the surface hardness isn’t sufficient or maybe doesn’t have enough depth, one of the lobes even has a bit of pitting. I don’t believe there’s any scoring on the journals but I’ll check when I’m back in the shop, nothing jumped out at we when I was inspecting the head though.
"I’m using mobile 1 full synthetic..."
mobil1 makes over 20 different oils.
The Shop
Paul, the bike ran fine on tear down, it was just getting a bit hard to start so I wanted to take a look before we start the next race season. I can’t imagine the valve is contacting the piston but I guess that is a potential possibility, it wouldn’t take much interference to cause issues. The piston and cylinder came from Cylinder Works and it’s not a high compression setup, do you think there’s still a change for interference?
did you run the bike for a short time then park it for a long time like a month then run it for a short time again and continue to do this.
do the oil passages look the same size as the ones in the orig head?
Are they billet cams or hardwelded?
Is there a machine shop near you that can do a hardness test on the cam and bucket?
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I’m currious what makes you think the bucket is concave? I’m relatively new to the four stroke game so forgive my ignorance.
As for the oil passages I’ll have to look again tomorrow, I can’t say for sure. This should be a stock head that is then CNC ported so the passages shouldn’t have been modified.
Thank you for your help so far.
"I know we checked the valves around 10 hours ago as well and noticed some wear on one valve bucket, so it was replaced."
Can you post a photo or describe the problem in more detail?
"This bike is a race only bike so yes, it does tend to sit for a while before being run again. Do you think that would be enough to cause something like this? "
It can but this is a very short time for that type of damage to occur in.
" I would have thought the residual film would be enough protection upon initial startup..."
Unfortunately not always, and the problem is greater in engines with high perf valve springs that are really stiff. This is one of the reasons I asked what oil you were using. It might be useful to know what your valve spring rate is also, and many shops that rebuild cylinder heads can check them.
Just a short bit of general info for now.
Welded cams can pit easier than billet cams.
If the base metal is too soft and the heat treating isn't deep enough, it can cause pitting and spaling if high spring pressures are used.
DLC coating can significantly reduce friction even damage from scuffing on "dry" start ups and reduces friction over non treated cams, but if the cam material is too soft anyway or the hardness is not deep enough etc, the cam can still get pits, so basically, this coating is not a cure for a crappy cam but can prolong a crappy cams life to some degree, but ideally it should be applied over a cam that is good to start with, in which case it can be a little redundant to some degree, but it really depends on the app and spring pressures as to how much benefit it will add. The higher the pressures and the harder the engine is run, the greater the benefit will be.
You can also get the cams coated with tungsten disulphide instead of DLC coated.
Ideally, the cams should be isf/rem finished before either process, but the isf process alone is an improvement over a non coated cam.
you could also have the cam cryo treated which may or may not do much for them depending on the quality of the cam material to start with.
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Paw Paw
To answer a few questions:
Unfortunately I don’t have any pictures of the replaced valve bucket. The bucket was replaced due to wear at the same time this big bore was put in (just a few hours ago), it may have been alright to run but I didn’t want to chance it because there was some obvious wear.
As far as the spring rates go, I just don’t have a good way to know if they’re much, if any, stiffer than stock, however since this was bought as a complete kit from GYTR as a bolt on replacement I doubt that it’s too aggressive of a cam profile or spring rate. I originally ran some Yamalube full synthetic but switched over to Mobil 1 since it was easier to pick up locally, so I just can’t imagine it’s due to inferior oil. Im wondering if you might be on to something with the heat treatment, especially since all 4 lobes show wear.
Here’s a quick update from today:
I started with a compression test to see if anything obvious jumped out at me. Unfortunately I think my compression tester took a crap because I was getting pretty much nothing, but I figured it was worth tearing the head off and taking a look. Upon tear down I did find some oil on top of the piston, leading me to believe the exhaust valves may not be sealing. However, I filled the head with fork oil (lowest viscosity fluid I could find that wouldn’t evaporate), and after a few hours the oil level had not dropped. This leads me to believe the valves are sealing, so hopefully we can rule out a bent valve.
One thing I did find interesting was two clean spots around the exhaust valves. Is this normal, or could it indicate that oil is passing through and the valves are in fact not sealing correctly? They are circled in red below, as is the bit of residual oil left on the top of the piston.
Upon tear down I found absolutely nothing that led me to believe there was any interference between the piston and valves. There were no scratches, nicks, or anything out of the ordinary really so I’m hoping we’re in the clear there.
I’m a little stumped as to how to proceed now. Should I just order up a gasket kit, replace the cams, and run some higher quality amsoil or something?
Something to keep in mind, mobile 1 likes to switch between class III and IV. III is not a real synthetic IMO. If you have a race engine itd behoove you to spend more time researching the correct oil for your bike.
Also send GYTR these pictures and see what they say.
Pit Row
Colintrax, the bike is a hillclimb race bike (real hillclimbs, not the freeways they run on the east coast), so it often sits for several months at a time between races. I wish it didn't sit so much, but you know how it goes with racing and budgets. . .
1. obviously call yamaha, but in addition to any questions you might have, ask them what material the cam is made from, and if it is a billet cam, and what the hardness is, and where the cam cores come from, not where they are ground, and if they had any other complaints/problems like yours. also ask what material the buckets/shims are made from.
2. get the existing cam, and any new cam you might get, hardness tested. it only takes 5 minutes and some places might not even charge you. this way you know exactly what you have and also if it is softer than what yamaha says it should be if they have that info.
3. if it is a hard welded cam, you can get one made from billet steel that has the same profile, but this might be fairly expensive.
4. a more reasonable thing to do whether it is hard welded or not, is to talk to at least 2 different cryo treatment companies and tell them what material the cam is and if it is hard welded and the hardness of it, and see what they say about having it cryo treated. cryo treating can get complicated on parts that are hardened, and in some cases it may cause some of the hardened material to become brittle, so ask the companies about this possibility etc.
if the cam can be cryoed and it sounds like it will benefit from the process, i would have that done to the cams and buckets/shims etc.
5. you will likely benefit some from a better and/or thicker oil, but i really don't think the oil is the actual cause of the problem, however, letting it sit for the long periods you stated can contribute to the problem, so to address this issue, i would also have the parts dlc coated or coated with tungsten disulfide as i previously mentioned, but again, having them isf/rem finished first is the best approach. dlc coating mare wear prematurely when applied to cast iron parts, but may adhere better to cast iron if the part is cryoed first. these are technical questions to ask any company that performs the dlc process.
6. obviously, having the processes i mentioned performed on the parts is a bit of a pita, and not cheap, however, i would still do it, because imo, it is a far bigger pita to have to change parts every 20 hours, not to mention the cost, plus additional damage these parts may cause if they continue to sluff off bits of metal into the oil etc.
7. magnetic drain plug.
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