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engine blow-by questions

mystryman said:
got the cylinders back. cleaned and oiled them. got bike put together today and went to fire it up. Now it seems like it wants to run on just the front cyl. front gets hot, rear barely gets warm. thought maybe I adjusted the pushrods wrong so I did that again...no change. hooked up timing light, its getting even fire. did a compression test, 105 front, 130 rear. huh?... so I did it again, same numbers....I don't get it.....I am really stumped now.
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Did you R/R cams during the rebuild? Do you have a fully charged battery? A less than fully charged battery will not produce accurate compression test results. Did you hold the throttle wide open when running the compression test? Did you have the pistons at TDC ON THE COMPRESSION STROKE when adjusting pushrods?

A leak down test to supplement the compression test should explain why one cylinder is holding more compression than the other.:hii
 
Yup, did all that you stated. Nonetheless, I really do appreciate all of your input. I found the culprit. Its the intake. I sprayed a little wd40 at the intake flange and the cyl came to life.
When taking apart, I had trouble with the intake. one allen head bolt would not break loose on front head , ended up rounding out the hex hole in the bolt and struggled to remove the intake, leaving the flange in the head. putting it back together had just as much struggle putting it back in, evidently pinching the rear flange seal. I gotta figure out how I'm gonna get that bolt out.
 
That does create a problem. If it was me I would take the head back off for more room. Try to use vise grips on it to loosen, then remove and replace. If that doesn't work then take a nut and tack weld it to the head of the allen, use a 6 point socket to remove it. Good luck with it and keep us posted. I would re-chase the threads afterwards.
tourbox
 
tourbox said:
That does create a problem. If it was me I would take the head back off for more room. Try to use vise grips on it to loosen, then remove and replace. If that doesn't work then take a nut and tack weld it to the head of the allen, use a 6 point socket to remove it. Good luck with it and keep us posted. I would re-chase the threads afterwards.
tourbox
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tourbox has you covered but if none of those work I think your only other option is to drill down the center of the bolt and use a EZ out. Surly not my favorite thing to do but sometimes you have no choice.:shock
 
mystryman said:
Yup, did all that you stated. Nonetheless, I really do appreciate all of your input. I found the culprit. Its the intake. I sprayed a little wd40 at the intake flange and the cyl came to life. When taking apart, I had trouble with the intake. one allen head bolt would not break loose on front head , ended up rounding out the hex hole in the bolt and struggled to remove the intake, leaving the flange in the head. putting it back together had just as much struggle putting it back in, evidently pinching the rear flange seal. I gotta figure out how I'm gonna get that bolt out.
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That explains the poor running but does not explain the low compression. One step at a time; get the bolt out and intake properly installed and you are ready for the next step.:hii
 
Ordered seals from j&p, shipped out by mail today.... gonna be a few days by snailmail...lol.
being that its still testing roughly same numbers after bore and new pistons, i'm wondering if previous owner might have shaved the rear head. but then, I don't understand shaving just one and not the pair. I dunno, maybe i'm just popping ideas in my head trying to make sense out of it....lol
 
Very good. PB Blaster is some pretty good stuff.
Now as Dolt stated your ready "for the next step".
tourbox
 
mystryman said:
Ordered seals from j&p, shipped out by mail today.... gonna be a few days by snailmail...lol.
being that its still testing roughly same numbers after bore and new pistons, i'm wondering if previous owner might have shaved the rear head. but then, I don't understand shaving just one and not the pair. I dunno, maybe i'm just popping ideas in my head trying to make sense out of it....lol
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Both cylinders are too low and the reason one is lower than the other is not because the previous owner milled on head and not the other.:D

IMHO, if it was my bike and the compression numbers you posted were accurate, no more testing would be required; I would bore cylinders and build a healthy top end. However, if you need more testing to point you in that direction, the "next step" is another compression test to verify the first readings and then a proper leak down test to see where the compression is leaking down.:D

Your first compression readings were 145/100, you had cylinders bored,etc. and now the readings are 130/100, something is definitely wrong. Forget what the Clymer manual says, a healthy EVO motor should see CCP in the 150-160psi range with both cylinders reading within 5psi of one another.

Do the leak down test.:hii
 
The last pressure test was with the damaged carb seal in. did again with the new s&s seals and all is good. Been getting it out a little the past few days trying to get some breakin miles on it. Runs and sounds great.
Had another thing I intended to work on after the engine, an oil leak under tranny. At first thought it was from oil drain plug because I had over-tightened it last time I changed oil, but on closer look found it was coming from a bolt on corner of oil pan that was loose. tightened it and one next to it that wasn't tight. leak still there. Well, first couple days of riding the leak almost disappeared, then came back a couple days ago. Checked oil level this morn and it showed at full hot level on stick. started bike rode it into the garage. shut it off and checked, back to full cold.
 
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