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Compression Just Isn't Right


mcaf29

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I know this should probably be in the engine forum but its probably gonna lead to a mod. When I bought my shee last year my engine came with 17cc domes :o and I live at sea level (so did the previous owner and he didn't tell me about them). He obviously didn't use race gas because the domes were heavily pitted. He also didn't weld the crank which began to separate (luckily before I even knew it was separating my buddy hooked me up w/ a welded hotrod crank. Before I even tore it down I checked the compresion and it was 150. I opened it up to find these 17 cc domes and Meats site told me it should be way higher than that. Well I rebuilt and put 19 cc domes figuring I would run race gas. After rebuilt it was still 150 psi (now its 145). I used two different gauges that are known to be reliable(one is brand new). I figured after awhile the pressure would build when the rings seated. Its now been several months and its 145. I did everything right w/ the dino oil and breakin. What could cause this? Could my coolhead be warped(I bought brand new o-rings)? If it is warped do I need to get a new head or can it be fixed by a machine shop? Of course if its gonna cost $150.00 I'd just get a Noss head. I torqued eveything down just like I was suppose to I used the method in my clymer. Help I really really cannot afford to pay someone to fix it right now.

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One thing to think about is the fact that all of the compression charts out there are for a motor with no port work. If you bike has been ported at all, that is to say if the height of the exaust port has been raised, you compression will be lower that what is listed on the charts. I would guess that you were somewhat down on compression before the rebuild and that resulted in the fact that you did not see much of a change between the 17 and 19 domes. If the bike is running good, not going through any coolant, and not getting hot, I would doubt that you have a warped or leaking head. I think that you are OK with the parts you have in the bike, assuming that you have done some port work.

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txblue,

 

I kicked quite a few times after it stopped moving at 45, I also had it WOT.

 

Blacksmith,

 

 

I don't think my engine has any port work (actually I'm almost positive). i did think exactly that though about why my 17's were so close to my 19's. That's why I rode it like that for a few months. It does pour smoke while I warm it up but I have yet to notice coolant loss. You just sparked a thought though. I have been checking the coolant level in the radiator and its been full but I've had to add some to the reservoir(I knew I was losing because it was spilling out). Maybe I was both spilling coolant and burning at the same time. I'll run it with the bottle empty and check the radiator (when its cold of course). Thanks.

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Is it just one side?? If not, then it has nothing to do w/a leak. Whats the chance of both sides leaking when the domes are bolted on separately and have the same compression......If you had 150 in both cylinders after rebuild, then you should have more. What are you running for oil and at what ratio?? Are both sides the same for compression?? Exactly??

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Bignasty

 

Yes they are marked, blinker fluid was changed recently so thats not it.

 

Banchetta,

 

Both sides are exactly the same compression. I mean it was exactly on the dot 150 and is now on the dot 145. This led me to believe that if the head is warped enough it allows the domes to lift just enough to let a little compression out and coolant in on downstroke. If its in the center I guess it could affect both. Of course this was just a quick theory and probably couldn't hold up to any scrutiny. Another theory is I cheesed on the yamabond during my last rebuild because I didn't want to over do it and somehow the tranny is leaking to the crank area(of course while puting on my new suspension I drained and replaced the oil without checking to see if it was low). I have no friggin idea what it could be. I run castor 927 at 40:1 and I haven't had this smoking problem before. I stopped by the machine shop today and asked if the bore or rings could be causing this and he said no cause even with good rings you still burn the oil(he says its either a bad oil ratio or I'm burning tranny oil). He did say I could pull the pistons and cylinders so he can check em out. Maybe I'll take a digi pic of the smoke so you can see how thick and the color of it(white).

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White!! You didn't say that before.....White smoke is a definate sign of burning antifreeze. If antifreeze is getting in, then compression is going out...Its just wierd how both sides are identical and have the same problem. Both sides smoke white?? Definately post those pics. Your also talking about after the shee is warm and not cold. Just making sure...

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O.K. I had this huge long post with pic links and my work computer crashed. I'll now do separate replies. I really thought I wrote white smoke but I guess i forgot to right that in. The coolant level has not dropped though. Its a kinda acrid smell. There also seems to be some noise coming from the engine (no kidding right). I mean noise that just doesn't sound right. The problem is i cannot pinpoint it. Its either water pump, crank or the pistons making noise, somewhere in that area. Maybe there's a reason I got that crank cheap. It of course could be me looking for noise cause I know there's a problem somewhere and its completely normal. I'll post pics.

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