Compression figures

[Captain Black]

Anyone know what the safe/normal readings should be in PSI for GS100 cylinder compression test ? How conclusive are any test results when looking for valve issues etc. Should add I used a gunson gauge so not sure how good or bad they are.
Thanks.

 

[Rob Farmer]

Max should be around 110-115 if your using 8.2:1 Pistons

As long as you get consistent readings on both sides that's all that really matters.
You are supposed to either take the carbs off or wedge the slides open with CV carbs

 

[Captain Black]

Max should be around 110-115 if your using 8.2:1 Pistons

As long as you get consistent readings on both sides that's all that really matters.
You are supposed to either take the carbs off or wedge the slides open with CV carbs

Thanks Rob, I have gone into shitting pants mode so I think I'm gonna take the haeds off just to be sure they're not toast. I'm off on a camping trip Tues so It will have to wait til I get back. Sounds like bad news If mine are up near 200 psi, although I did'nt have the slides up or the carbs off. I'll take It to bit's next week. Thanks for your help.

Just to mention I checked the valves and i can slide the gauge .10mm / .20mm In and out but If I'm honest they're a bit tight!!

 

[Rob Farmer]

Sounds ok if you can do that. Just do the compression test if they are both about the same you should be fine.

 

[Smug]

Your gauge is reading too high.

Compression test should be done on a hot engine with a plug out of each cylinder and full throttle. Crank for the same amount on each side.

 

[Captain Black]

Sounds ok if you can do that. Just do the compression test if they are both about the same you should be fine.

Think I've gone off Into the world of high compression! Following on from my "cherry red" exhaust on the left cylinder I have re done the valve clearances, they were and still are a mild to firm (but not over tight) .10mm inlet and .20mm Exhaust, everything looked fine so I did a compression test with my shitty Gunson Hi-gauge cold engine, fully open throttle opposite spark plugs in place. Anyway both cylinders are aalmost exactly the same at 195 psi each. Did the same test after running the engine for 3 mins to get some heat Into It. Both cylinders read 210-215 psi. The motor sounds as sweet as a nut, yet within a short time, ie 3 mins the left header started to go red hot again! Not sure what to do for the best now, oh just to add both spark plugs seem to be normal a nice shade of brown/light brown. I wonder if i could get a bore scope down the plug hole and have a peek ? Seems odd as the engine does not make any bad sounds. Any thoughts ?

 

[Beemerboff]

Last time I saw an exhaust glow red was when my mate was tuning his old v 4? Transit van, and he made it glow by retarding the ignition - the distributor could be advanced and retarded with a knurled nut at the base, and he turned it the wrong way.

But just how an airhead could be that retarded on only one side with BMW's wasted spark system I cant imagine.

 

[Smug]

Your cheepo gauge is not calibrated correctly.

Headers do sometimes glow especially when the bike is stationary.

 

[Captain Black]

Your cheepo gauge is not calibrated correctly.

Headers do sometimes glow especially when the bike is stationary.

Funny you should say that. Even with the pressure released from the gauge the needle Is stuck on 60 psi !! Is It to simple that I reduce my readings by 60 psi thus giving more realistic figures ?

I'm trying to search google re the glowing headers but everyone seems to have a different slant on It. From It being totally normal to all sorts of causes and impending doom
Perhaps I should start a new thread, and see If we can get some test going to see how many do start to glow after a few mins. I really only noticed It because I was In smi darkness In the garage last week. Maybe It's always done It ? I dont know.