I have an '86 250R. I bought it used and it had an '88 Paul Turner ported cylinder on it. It had been resleeved and was at .020. It had never been ran on my quad before I bought it. It blew 2 head gaskets in a row and I got serious blow-by and puts pressure in my cooling system, causing my hoses to blow and my coolant reservoir to fill up. We tried shaving the top to make it smooth but it still did it. I tried a different head, a cr250 head gasket, and even permatex, but coolant still gushes from around the top of the cylinder. I put another cylinder that I know was good and it solved the problem. I have talked to a lot of people and nobody knows what is wrong with that cylinder. I hate to scrap it, does anyone know what is wrong with it? Please help.

 

You need to make sure that both the cylinder deck and head are perfectly flat. Have they both been put on a plate and checked for flatness? If both are flat, then they should seal up. Also, the CR head gasket is prone to blowing because it's extremely thin. I'd recommend checking the head and cylinder deck for flatness and going to either an ATC or TRX head gasket. Good luck.

 

Are you running race gas? Reason being that engine sounds as if its built to where it needs probably 110 octain fuel or so. It may sound too simple a fix for what may seem a fairly major problem, but I just had a friend blowing head gaskets like crazy on his 350R he bought from another friend, then I asked what fuel he's running, he replied, "92 octain". Now he's running race fuel and has no problems. Also be sure your running the right piston, an 88 engine is a long rod, whereas an 86 is a short rod, unless it's been modified.

Also, did you change anything, it sounds as if you swaped cylinders from one engine to another, if thats the case find out everything about the engine, sometimes they will build them to run totally different pistons, like a YZ 250 piston for example. And a CR gasket is thinner than a TRX gasket, so be sure you use all the right parts, you should ask the original owner what should be used for gaskets and pistons, even giving the engine builder a call would be a good idea. When you buy stuff like that, you have to do research sometimes to know exactly what you have or are getting into.

Good Luck,

Sickman

 

Thanks for the input guys. I have a problem with asking the original owner of the quad questions about it because he past away. He was only 23 years old and was a great rider and he overdid it in the memorial day race at our local MX track and crashed and died almost instantly. But, the good news is that his mechanic/sponsor is who sold me the quad and is now helping me out with it. The thing is that when Steve passed away, his mechanic gave the cylinder that was on it to his other support rider who rides GNC 250 pro-am, #8 Darrell Dudley. Then he put this cylinder which they got in a trade on the quad before they sold it to me. My quad has an '88 crank and had an '88 piston when I was having these problems. My mechanic had the head shaved and the cylinder decked and they matched up perfectly. I tried cometic gaskets along with the ATC gasket that Witz mentioned and it still did the same thing. I do run 93 octane gas. But, when I put this other cylinder on, I switched to an '86 piston with a spacer plate and I still run 93 octane gas and it works fine. Could a water jacket be cracked in that other cylinder? Anymore suggestions?

 

I guess it's one of those things where it would be easier if I could see it. But I would first check the compression to see what you do have for sure. You just may have too much for 93 octain yet, I couldn't tell without looking at it though to see if the cylinder has been decked much or not. But yes, inspect the cylinder well to see if there is a crack which could be a possibility.

I think your best bet though would be to ask the mechanic that swapped the cylinders what parts were run as far as crank, piston, and how thick of gaskets. I've seen and heard of people do some strange things with there engines like using different pistons as mentioned earlier. Maybe it would be good to have that mechanic take a look at it also, to get their oppinion. If they got the cylider in on a trade, then maybe there was a reason the owner got rid of the cylinder, and the shop or dealer or whatever inadvertantly gave you a bad part, if so they should be willing to help you out to get it running again.

Good luck again,

Sickman

 

If you think that the cyl. could be cracked some where try taking it to a machine shop and have them magnaflux the cyl for hidden cracks, it might help elimanate that problem. Also try running FACTORY gaskets, I race with guys who swear by factory gaskets, because aftermarket gaskets are cheap in quality (price vs price) If your cyl and head are shaved use the 4 trax headgasket it is the thickest of all the gaskets. Your cyl. might be shaved to much. And definitly run race fuel you have to much compression for pump fuel.

 

I really appreciate it guys. I never thought about magnafluxing it. I will have to check into that. I didn't know that if you have high compression that you must run race gas. I know that it had a ton of compression after we shaved it and it was very close to hitting but it didn't. You guys want to explain to me about race gas. I am probably going to start mixing half 93 octane and half 110 octane, do you think this is a good idea? What are the advantages of race gas? Thanks again for your help.

 

Why didn't you say you shaved more off the head than was already done (From what you said, it sounded as if the engine was already midfied by Paul Turner and maybe they already did decking on the cylinder and shaved the head). From what you just said, I'm willing to bet that all your problems are from not running race gas as I mentioned in the first post or you just plane took way too much metal off. Race gas is higher octain and better quality than 92 or 93 pump gas. Higher octain isn't a power booster as some people seem to think it is, it's actually more stable the higher the octain rating is. This does you no good to run race fuel in a stock engine because it will actually make it slower, BUT A HIGH COMPRESSION RACE ENGINE REQUIRES HIGH OCTAIN RACE FUEL. Reason being, the high compression causes too low of octain gas to denotate (Prematurely explode and try to force the piston down before it reaches top-dead-center). High octain fuel is more stable, thus does not denotate, thus not blowing out head gaskets and grenading a piston, rod, and crank. yes what you are experiencing is VERY HARMFUL to an engine.

Also, wasn't the cylider and head already modified before you shaved it, you said the piston almost hits, but not quit, well do you have TOO much squish now.

I don't want to sound harsh, but my advise (I don't know who is playing with your engine, an actual bike mechanic or a mechanic wannabe), but I'd get another mechanic to take a look at it, it almost sounds like whomever is currently doing the work maybe doesn't know what they are doing. If you have so much pressure that the cooling hoses blow off, you have way too much compression. Also if your mechanic knows what he's doing, he should know exactly what compression your engine has, so he should have mentioned if you would need higher octain race fuel or not.

I hope you get it figured out, but I still think you need somebody else to take a look at it before that cylider is destroyed. If nothing else, my sponsor is an excellent mechanic and he is a machinist by trade, so if you really want it figured out, he can. I'm searious, if you get tired of it (I know what its like to be frustrated as you must be, and sometimes its best to just let somebody else play with it), his name is Scott and his place is SORE Racing at (319) 462-6709. He is a super nice guy, and I know if you sent him the cylinder and head, he could find the problem. I'm serious, give him a call and see what he thinks.

Like I said good luck, and everybody's been through it so hang in there.

Sickman

 

Everyone here has given great advice to this guy! I have to agree that the problem lies in having too much compression. You should never run a CR head gasket on a modified head. Those things are paper thin. There was a local guy racing here in Michigan and he has the stupidest engine builder. He was running over 240lbs. of compression and he was using CR head gaskets. I think that is pretty dangerous! I guess he enjoyed grenading his motors. You should just use the same setup that was used on the bike that your "new" 86 cylinder came off. If the bike has a long rod and you are using an 86 piston then you better have a spacer plate or the piston will be hitting the head. If you are using a short rod and an 87-89 piston then you will have very little compression I don't know what your setup is, but you definitely need to find a competent mechanic.

 

Hey I really appreciate you guys taking the time to help me. Thanks for sticking with me Sickman. I guess I will wait until this summer and I have a little more cash. I will try that cylinder again, and have the compression tested and try race gas. If this doesn't work I might send it to Sickman's mechanic. Thanks again guys. When I have more questions I will definitely know where to ask.