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Compression: 125-120-118-0

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

Guest
That's right boyles and goyles... I did a compression test tonight and those are the numbers, cyl 1 is reading 0 psi. Which is odd because it seems to fire. I have a little valve chatter from this cylinder, but I don't see why it would read 0 PSI with a little valve chatter and still fire. I'm going to go out later and jump start my bike again (killed the battery with the compression test.) I also poured a little oil down the cylinder and nothing changed, so if anything, it's the valves. Any other ideas?
 
Sounds like that 'valve chatter' is more like a valve failure. Even if only a portion of the valve remains, when the engine is running fast enough it will create enough compression to ignite fuel. won't put out alot of power, but will support combustion. Hopefully it is only as simple as a valve adjustment to take care of it. :twisted:
 
You'll need to set the valve clearances first. It may be that your valve isn't closing.

Steve
 
It needs your imediate attention. You may have a bent valve?? Has the bike been over reved reciently?? The motor could destroy itself if you break a valve. Checking the clearances should shead some light on the problem. If the valve adjustment is Ok you will probably have to remove the head to check it further
 
Unfortunately I do not know much history on the engine. I can tell you it hasn't been revved above 6000 since I purchased it, however I goofed on the timing the first time I installed it. I was 1-2 teeth advanced on the exhaust or 1-2 teeth retarded on the intake (there were only 18-19 links between the two instead of 20, I can't remember which). It sounds like I'll be mounting my spare 750 motor while I rebuild this one... after I extract a few broken bolts from the 750. I know this has been discussed before, but will the 750's head fit? It's a year earlier, 78 instead of 79, but still an 8 valver, I also understand that the bolts line up, but I'll be boosting the compression slightly. Are the valves and ports the same size? I intended to install a stage 3 jet kit for a 79 1000 with pods and 4-1 exhaust, (which will still be on the bike) but there isn't a jet kit for the 750, which concerns me about valve size and such. This really disappoints me since it is finally warming up and I have several long trips planned for this summer, and I intended to perform several performance increasing modifications including cam degreeing. I even plan a UROP (Undergraduate Research Opportunity) for making my bike a turbo-charged sleeper (completely hidden turbo) or if they let me, cutting an entirely new engine design, but all this takes money I seem to be dumping into this engine because the seller lied to me about the condition of the engine. When I balanced the carbs, number 1 was only pulling 6 inches of mercury, but was easily adjusted up to 18, so it does pull vaccuum, it just doesn't compress. Lets pretend I have a bent valve. I need a valve extractor (probably rented from Ace or some other tool rental place) and what else do I need? How much will new valves cost? do I need to lap them if they are new? How hard is the carbon buildup to break off? I rebuilt my 750, but I skipped the valves due to the broken bolts in the head. I broke up the carbon with a die grinder, but I don't know if that was such a good idea. HELP!
 
If it was mine I would remove the head and remove all of the valves
(make some kind of holder out of a box or? to keep them in the correct order that they were removed from the head) Take the head to the local machine shop and have it chemically cleaned. After lapping the valves CLEAN, CLEAN and CLEAN again
 
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