Low compression repair options

[RadiumPHX]

I found that the cheaper compression testers, i.e. harbor freight, do not have a shrader valve in the connecting hose and will only give 1/2 the actual PSI. Same thing happened to me, got 90 PSI and was forlorn. After testing another bike and getting similarly poor results I suspected the tester. Purchased a better one at the parts store and got 170+ from all cylinders.

 

[Screwloose]

Pop the carbs off their seats and raise. take the plugs out. Then Nice free turnover of the engine. Thats what i always do to make sure before engine comes out.

my gsxr is showing drastically uneven compression in two cylinders, put in some oil and they come up to the other two at correct compression, so definitely i have rings/valve/seats issues, or all three.

But having all readings the same is not completely unheard of, just a bit unusual in my opinion, it could happen if sitting a long time and trying to turn a dry engine over without preparing for it, then tearing up dry valve seats etc.

 

[DreamV4]

Your engine is most likely fine, usually one cylinder is bad. Possibly slow turning starter, bad battery. You also can attach charger to avoid battery discharge from first to last cylinder compression test.
Replace oil with 1qt of ATF + 20w50 (or 60 from Harley dealer). You can also add "Stop smoke" if you want more viscosity. ATF will clean piston rings .

 

[Redcardbob]

A quick follow up on this post...
Suspecting that the engine ran better than it should for being so low on compression, I borrowed another compression tester to compare readings. The harbor freight tester was showing me about 90 psi, while another better quality unit was showing me 125!
I'm still gaining about five psi by putting a little oil in the cylinders, so I may have a little ring blow by, but not as serious as I originally thought..

By the way, I am at 5800 feet, so the correction factor brings me within spec.

When it comes to tools, quality matters!

 

[DreamV4]

Important thing is to have equal compression. I would be happy with 125, except you need ATF flush for piston rings.

 

[Redcardbob]

Important thing is to have equal compression. I would be happy with 125, except you need ATF flush for piston rings.

Yep! They are all within 5 psi of each-other. I'll try that ATF trick. How long would you run it before draining the ATF back out?

 

[DreamV4]

Yep! They are all within 5 psi of each-other. I'll try that ATF trick. How long would you run it before draining the ATF back out?

Ride with it. 1 pint ATF, rest of oil 20W50 or straight 60 from Harley dealer.
This is my own idea, you need to match viscosity. Get a beer can, make hole, fill it with 10w40 and check time to drain, then do same thing with my mix. Whatever you feel OK. I always used ATF for hydraulic lifters cleaning in car engines.

 

[Hadden]

I recently did mine and they came out at 90 with throttle on full, but I didn't realise it should be done warm! What sort of difference would it make in terms of numbers?