Factory compression ratio.

[Rat]

Well … let the rest of us know if there’s a get together in the offing … hate to miss a get together, there’s usually beer involved …

Al has been quiet on the forum for a while … life and a new job involving a lot of travel are keeping him busy … but he’s in good health and thriving

Gord

[CYBORG]

Weather being as good as it has been I think there is time to sneak in one more get together. When are you coming cross the border next?

[Rat]

Guess we hijacked this thread … sorry Cliff …

Gord

[gltriker]

No worries, Gord. I didn't start this topic

[redglbx]

Cliff, thanks for the kind words ??? No baiting involved, but just as I said at the start just some coffe and rambling thoughts,,, been a lot of conversation on this subject over the time I’ve been on this forum with a lot of opinions stated, some valid , some just pure BS…… Again I don’t know how I somehow baited you in,,, quite frankly I really don’t give a damn ! But frankly I noticed that your are still reading this thread !

Oldwing,,,I think your 1100 results are more typical of the newer bikes that are 78 and newer motors because I believe that they run cams that have less duration and overlap trying to be more torquey vs the 75-77 motors that were more”hotrod” focus’d with cams that are much more aggressive with more duration and overlap.. Over the years I have compression tested a number of the 78 + 79’s and most come in the 160-170psi range..

but not trying to bait you in on this !

[redglbx]

Ok this is my last post on all this,, I promise.. so I bought a new calibration grade (+/- 1% of full scale) digital compression tester graduated to .1psi increments… to replace my 50+ year old tester, sigh ,,,, the new one still had an adapter ahead of the Schrader valve that added about 4cc’s of displacement.. I ran it as delivered and it had a consistent 187psi reading across the board… so then I made a plug to eliminate the added displacement ahead of the Schrader valve and it bumped the CR up to 192.5 psi,,not bad !

So at this point I decided that I wanted to know what the actual difference was between the.004in and .006in valve lash was, so I checked and found initially that it was set at .006in , I was probably looking to get a little more compression and torque since my compression had been nose diving for a few years … so the.006in lash gave me the 192.5 psi number due to less cam overlap..

So I readjusted the lash to .004in which gives more overlap and .002in more lift, should make more power at the upper rpm’s . The .004in setting gave me a cranking compression of 187.8psi…. By the way this was all done at cold temps (ambient) ,,, so I guess I need to make one more installment once I get it running and take the compression with the engine hot,, should go up some..

So again how does all this bear on your engines performance ? Outside of the valve lash adjustments it doesn’t,, it’s just pure diagnostics to compare cylinder to cylinder for any problems.. the .006in lash should give you a slight bump in torque and low speed performance while the .004in lash should then give you again a slight bump at the upper rpm’s range.. I really wish I still had access to my buddies dyno to be able to dyno the differences the lash makes, I’d bet it ain’t a lot.. so at this point I’m done but will give an update once I can test it hot..

[robin1731]

[redglbx]

Agree Robin , but all this comes up periodically usually for a newbie, so hopefully it’ll be helpful