Sorry, I didnt see the 2nd page here![img]i/expressions/face-icon-small-blush.gif[/img]

 

Ok wait a minute, I am not pointing the finger at Forward Motion. I know that Eric Gorr is an expert tuner and both him and his company are extremely reputable which is why I sent him my motors. When Eric and I spoke on the phone regarding the 250R jug I asked what can be done to this motor to squeeze more power out of it and his reply was raise the compression ratio. Ok sounds like a good idea, but I still need to run pump gas.

Now correct me if I am wrong but the bike would not have run worth a crap, if at all on normal 92 pump from the local Texaco station if the compression ratio is calling for 110? (That would be like trying to light some BBQ coals with 80 proof vodka) There is an excellent possibility that my compression tester is giving me a false reading. I would have needed to test the bike with at least 2 more compression testers to know that for sure and I didn’t It also may be on some different type of scale other then PSI. I am not sure, I didn’t look that close yet.

One thing that I am concerned about is piston clearance. The Weisco box reads: 68mm (.0030 clearance) when I have been told that for a 250R, .0045 is the minimum. This would explain why the bike did not fail on me during the heat cycles, the piston and the cylinder walls heated up around the same rate of speed because there was no load on the bike right? Well when the bike did fail, it was not warmed up for an extended period of time like it had been during the heat cycle phase therefore the piston would have expanded faster then the cylinder walls. With such a small amount clearance (.0030) the expanding piston got to a point where it started to rub against the cylinder walls and then BAM, gonzo.

And then of course we have the air leak theory which is more then likely why this bike is not running right now. I used all the gaskets that were provided to me by Forward motion which were a cosmetic top end kit. The base gasket was just your standard size and thickness from what I know, and this gasket fit like a glove. However the cap gasket did not fit worth a crap any way I tried to put it on so like I said before, I had to force it on the way I was told (with the little tab pointing towards the exhaust port).

I would like to thank everyone who has read, and replied to this thread. Everyone has been very helpful in troubleshooting what the problem is here. I will continue to check into your suggestions and report on what’s up with the R. But as it sits right now, I am leaning towards either air leak, or piston clearance.

 

You did (or bore guy) did releive the exhuast bridge did you (they)....this is a must.

 

Not sure what you mean by exhaust bridge? are you talking about the bar that runs vertical in the exhaust port right in the middle?

 

Yes, that's the one. It will tend to swell into the exhaust side of the piston and could score it slightly making the ring stick. I would pull the pipe off and look at the exh. side and see what you can find.

 

So do you only have to relieve the exhaust bridge if you bore it or do you have to do that when you hone it too? I am putting a new piston and rings in mine, but the bore wasn't bad and I just honed it out. Should I still round off the bridge?

You wouldn't have any pics would you?

 

The bridge will have to be relieved in a BORE situation. If you are just crosshatching the cylinder/de-glaze then it should be fine, But I would still take some fine grit and scrub that bridge good. The short rod versions of the R motor were more prone to locking up due to heat and wear.

 

Looking at my piston, it would apear that both the exhaust side and the intake side of the piston rubbed pretty good. Also there is a little bit of chipping on the edge of the dome where that exhaust bridge would be in between the dome and the top ring, not sure why it did this. If what you say is correct and that bridge must be removed then I must say I am a little disapointed that Forward Motion did not do this. I gave them free rain on the mods at long as it was reliable and could still run on pump fuel. This is the second time this bike has done pretty much the exact same thing but the first time I just wrote the problem off as improper jetting, now I am starting to wonder if I do have a air leak.

The first time this happened I had just got the whole motor back from a local mom and pop shop and only got a few hours on it that time as well as this one. So maybe when this guy put the case back together from replacing the crank, he did not get a proper seal. I did notice that Forward Motion used some type of gasket sealer on my CR 250 so maybe I will try that on this R motor just to try and ensure that I do not get another air leak.