Low Compression?

My check with thread-in compression gauge produced the following readings:

cyl #

1-135,

2-135,

3-130,

4-145

Should I be concerned, and is there a correlation between those readings and the need to add oil to the engine often?

Cold engine? Then their fine

If you used a compression tester with a really long hose and the check valve is at the gauge, then the numbers come out much lower than they really are. What happens is that the volume of the hose becomes part of the combustion chamber and it lowers the amount of air pressure being compressed into a now larger space.
If your tester has the check valve right at the threaded end that goes in the head, then you should be worried. But your numbers are close together so I have a feeling it is just the gauge (the hose) that is skewing your results.

Is the check valve for the compression gauge located in the gauge itself or near the cylinder side of the adapter? The valve in the gauge side can cause lower readings due to the adapter tubing adding unwanted cylinder volume.

The numbers themselves look satisfactory. Not great, but not really setting off any alarms. In my eyes, a top end rebuild would only be done if it was accompanied by another symptom, like poor running, valve seal leakage, and maybe even burning oil if the cause wasn't an external leak.

Does the bike run well? Any issues through the power band, any evidence of oil loss via smoking or fowling of plugs?

To get correct compression values you have to crank minimum 10 revs with full throttle on a hot engine.
Only so all valve seats surfaces, piston rings, oil and tolerances are in a driving condition.

The check valve should be right at the tip of the compression tester, as far into the plug hole as possible without extending in any further than the spark plug would, obviously.

There are many kits that have the check valve near the gauge. When testing a small engine, that type of tester can possibly cut the compression reading in half.

As mentioned, it all depends on the volume of the hose before the check valve.

Thats why you have to crank more than 10 times to get the highest value as a real value.
And all spark plugs out to get full revs as you can.

Warm engine, 5-6 revolutions, 12"+ long hose w/release at the gauge base ...Hmm.

Chit...maybe the engine is ok after all, but I'm having to add oil oftener than I'd like. But I like winding the upper rpms...can't help it. :blink:

Thinking of going to Shell Rotella T for a change. Brad Penn V2 oil is pretty expensive, and maybe the engine needs something like changing shampoos is good for your hair once in awhile.

So you think your piston or piston rings blow your oil through the exhaust.
Out of my experience the valve seals are weak, they do the hardest job of all seals and are the first that lost their sealing properties.

Far as the oil going out the tailpipe... The outside of the baffle is dry (not oily) with a brownish color to it.
New Viton seals were installed early 2015, and that was just before this head was nutted on my engine with 42 ft. lbs. torque.



A wee-bit closer...


Been riding since early last year with over-rich jetting. Found that out when I had the dyno pull a couple months ago. Since then I've leaned it out considerably, and been thinking of trying the 15.0 pilot jets next time the carbs are off.

Thanks guy's!

Looks good.
Steve

You mentioned release. The pressure release for draining pressure when the gauge is done being used is ok at the gauge base, it's the Schrader valve you don't want at the base of the gauge.

If you don't have any residue or performance impairment and you like the way the bike rides, ride it.

The question comes whether a rebuild or teardown is worth fixing having to fill up or top off. As more issues arise throughout owning the bike, that question becomes easier to answer with more time, eventually becoming absolute on a long enough time line as things break and wear normally.