Howdy guys, looking for opinions on a blown head shim. I am running 240 MCX kit on a 08 Nytro. I put on 1600kms no problems till now, on a high speed pass lost compression on two cylinders, on engine teardown found headshim blown out between two cylinders and the other not far behind. So far all we can come up with is I over boosted possibly from the automatic boost control which the MCX kit is built with. I have damage on head and block(will need machining now) hence increasing compression again. Does detonation cause this failure?? Do I tear down entire engine to look for damage below pistons. There is no evidence of damage on what we can see from top now. No marks on cylinder walls at all. I have heard of the auto boost contol freezing up, has anybody else?? Any opinions would be valuable. Never thought this day would come from my Yamaha!!
Troubleshooting blown head shim
- Thread starter Mountain Bound
- Start date
If you don't have to worry about detonation if you don't see any signs on the top of the pistons. I would say overheating may be something to look into as well.
Wouldn't it have thrown a code if it overheated??? Nothing came up when she went down or shortly thereafter.
what kind of damage on head and block.
Running too much boost could cause some head lift which in turn could cause the shim to be destroyed. Not sure if anyone has problems with head lift on the nytros, i know it was an issue with boosted honda cars so we ran arp head studs to help stop it.
Where the shim let loose they look like just 2 scratches in the block and head both(matching), my guess I have to eliminate this, will give it a easy path to go through again. The scratches aren't that deep but will have to be removed. Still have an uneasy feeling on what caused this mess so have contacted MCX themselves, just waiting for reply. The head bolts are necked down, stronger ones should be available. Please keep the info coming if you got it.
Thanks.
Thanks.
Actually it was towed by Nick's XP, I am still traumatized.
Hey Chad, sorry to hear about ur troubles.....how did u like the Nytro compared to your Apex????
Good luck with the headshim
Good luck with the headshim
Thought it was great till now. How's riding been this year??
The head shim is put in to help with detonation due to boost. Even with the head shim you can have too much cylinder pressure from overboosting. Without using aftermarket head studs I would not boost over 18 lbs. Over 18 I like to see stronger head studs.
Detonation will erode the head shim
Is the mark on the case and head measurable?
Is the mark on the case and head measurable?
No, it looks more like a scratch more than anything. We checked the head for plane and it it excellent, not warped at all. Engine builder figures the "scratch" won't be problem. Have ordered a set of Alpines head bolts(stronger). Installing a manual boost controller as well.
Thanks for the input guys
Thanks for the input guys
My guess is lift from excessive boost and not using special head bolts made to take the increased pressure.
Are you running a boost gauge and if so what boost, is it getting spikes?
I am running a gauge but have not noticed any spikes. We are questioning the altitude adj for boost and thinking it may have froze up. It was minus 24 c when she went. I was running about 12 pounds for about 5 miles then I went wide open for probably 2 miles, she was Frickin movin!!! She went down on full throttle, and no codes. Maybe I just pushed it too hard(14 to 15 pounds) at 2500 feet. We are replacing the shim putting in tougher head bolts and going to run her. Off to Cooke in a week, hopefully all is well.
wide open for 2 miles, I would say you most likely were biulding some heat in the motor. lucky thats all the damage.
It probably wasn't two miles, lets say it is 30 to 40 seconds, not long. I would think this is not out of the ordinary comparing it to some of the long pulls I have seen, the temp may have been the contributing factor!! Little chillier than the mountains.what do you guys think.
what kind of fuel are you running? they say pump but i have one and i don't think it should be run on pump fuel past 12lbs. Also if your running 240 kit, you need the extra fuel pump past 13lbs or it will run lean because fuel pump can't keep up. do your pistons show signs of detonation?
Similar threads
