Pumping Compression

[petejw]

Hey TC,
Did you get a chance to check your valve clearances?
after the rebuild the valves may have closed up a bit, adjustment might help
even out the compression, i had 3 closed intakes, and no2 was slightly lower in compression, all evened up and made a huge difference to the engine.

[Dan Hodges]

A WTF Moment

Hey Dan,

This won't complete your database, but I wanted to provide the followup data that I promised compared to my 'just broke in' data.

It had been a long time since I had checked it, and while I was doing a bunch of stuff on the bike today, changing oil, new plugs, the cam chain tensioner, I did the comp test. The values I got were:
105-115-100-90 I thought, my god, what have I done to it!

Then I had the DOH moment, and realized that I had not had the throttle wide open. I've instructed many others on this, but just forgot! So folks you see it DOES make a big difference in the values you get if you don't use WOT!

The WOT values were:
170-165-155-160. They are within 10% of each other, although #3 is lowest. I didn't try adding any oil.

Again, these are on an 81SH with stock cams, valves, just the 1179 and graphite head gasket, now with some 16K miles on it. Nice to see/read what you said about BigLeo's readings for using 93 Octane, that's what I use in it.
Hope you get the early model values soon!
T.C.

Hi T.C.

You are not the only one to have had a "DOH" moment as I've had some real dandies myself. Based on Leo's stock stuff with the 1179 kit, your numbers on 1&2 might be a trifle high but the bigger concern is the variation between cylinders 1 and 3. I would put 1 cc of oil into each cylinder one at a time to verify that the valves are sealing properly and then do a leak down test to check the ring seal and if your leakage is less than 5% (8% will do) then you know you have a motor that is sealing well but might have some carbon residue problems. Somebody mentioned valve lash which will effect it but keep in mind that it takes .003 of lash to change the cam timing by 1 degree. Nobody mentioned what happens to the cam timing when the cam chain is too long/wore out/too much slack/not adjusted properly/bogus cam chain tensioners and etc..........oh sh-- I've got 180 pounds psi and it's starting to rattle, stand back non believers she's gonna blow! The valve lash on the late cams should be .004 to .006 on the intake and .008 to .010 on the exhaust. The early cams get .006 to .008 on the intake and .008 to .010 on the exhaust and so as you can see there isn't much clearence to play with. On engines with rocker arms, valve lash can have a somewhat greater effect on the cam timing depending on the ratio of the rocker arms however the XS doesn't employ rocker arms as the valves are actuated directly off the cam lobes. Thanks again for taking time out from your busy schedule to share your tune up numbers with me because this kind of information is extremely hard to come by. Now if I could just get some numbers on some 78-79 stuff with the Wiseco's I could ease up on this Maxwell House and get a life.

Dan