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no compression but head, cylinder and piston look fine; &%$#@!!

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I'm rebuilding the topend on one of my DRZ because it has little to compression, but upon taking it down nothing seems out of sorts.

 

Head looks fine, no marks where cams have gotten into the head, piston looks fine, no gauges or major marks in the cylinder either and the crank is still snug so basically even though there is no compression everything looks fine inside???

 

compression test showed next to nothing and pressuring the cylinder didn't show any leaks in valves so &%$#@!???

 

guess I will delve into the head to see if anything gives there, but just seems odd that it would be so low on compression and there not be obvious issues, heck I half expected the piston to have a hole in it

 

oh well I have a CW 434 bb kit on the way and I already have another head so the problem will be solved regardless, just seems really odd there isn't an obvios issue given the compression is next to none

 

I've never been so disappointed not to find something wrong

 

thoughts???

 

before you ask here is what all has been checked thus far

 

valves in spec

spark plug changed

no damage to head from cams

cams turn freely

engine turns freely

cam chain fine

timing correct

tried to pressuring cylinder with a little oil, still next to no compression

engine turns over easily by hand

valves return and seat easily and quickly

nothing leaking, no sign of damage other than won't crank

 

just seems really odd that a bike that won't crank and with next to no compression wouldn't ahve some obvious things showing when you check the head, cams, cam chain, valves, piston, cylinder and crank

Edited by dirtdude723

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My guess is the rings are stuck/sticking in the grooves.

It has happened before.

Edited by Black_DRZ

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Compression gauge is toast/ not installed properly.

Rings are all lined up so the gaps are lined up.

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You need to run a leakdown test .

Use compressed air

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If you pressurized the cylinder you would of herd air leaking by something. Even if the motor was making compression you would of herd air leaking out from somewhere.if the head if off try filling the combustion chamber with water so the valves are covered and blow compressed air into the exaust and intake ports and see if you have bubbles come out from the submerged valves

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Broken keyway on the flywheel, meaning the starter wont turn it anyway if its spinning on the crank, even with toasted rings the thing will have some compression simply by fast displacement, decomp, burnt valve, &%$#@!ed head gasket, without looking at it who would know

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Did you tear it down based soley on the compression test? .... we're there any other symptoms ...ie poor starting/running, oil consumption ..... I have seen on here may times that a compression test is worthless unless you disengage the decomp. 

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This thread is one I will point to to show why full diagnostics need to be done BEFORE teardown. That includes taking it to someone if a riders less complete abilities, tools, ect leave the problem unresolved. 

 

Low or no compression is one of the easiest faults to pin down while the motor is together.....a leakdown test done correctly will  point to the failure point, and then further inspection will tell you why. 

 

To the OP, none of that is intended as disparaging remarks to you.. But a reminder for others that find this thread later in a search.

 

For your issues now...

 

For sure check the rings, see if they are compressed and stuck in the piston grooves.

 

Sure check the head and valves for leakage .. though I'd skip the water idea and use solvent.. if the valves are leaking any appreciable amount, you'll see solvent trickle into the intake or exhaust tracts. 

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Do a differential compression test. They are pretty easily built from info on the net. Mine showed leakage past the piston and the rings were frozen, they wouldn't expand out to the bore.I don't have a clue how that came about. Or you could just remove the cylinder and piston and check

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UPDATE:  upon further investigation it appears the intake valves possibly were not seating properly because the lip on them is much deeper and grooved than it should be which would make sense given that it was getting harder and harder to start but then once warm it was fine

 

good news is I have 2 DRZ 400 E models and 3 heads, 3 sets of cams and also 3 sets of valves so plan is to check out valves on another head and either swap them out or just use the other head I have that is good. One head is worthless, cam got down into cam journal, but the other two heads are fine.

 

Other good news is my CW 434 kit and FMF full exhaust arrived so the plan for tomorrow after work and maybe Sat if needed is to assemble one DRZ, likely the street legal one, with the 434 big bore kit, good valves and head and get it broken in to ride Sat or Sun :-)

 

Thanks for all the suggestions and input, hopefully the valves are the problem and will be easily solved, if not I will update.

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UPDATE:  upon further investigation it appears the intake valves possibly were not seating properly because the lip on them is much deeper and grooved than it should be which would make sense given that it was getting harder and harder to start but then once warm it was fine

 

good news is I have 2 DRZ 400 E models and 3 heads, 3 sets of cams and also 3 sets of valves so plan is to check out valves on another head and either swap them out or just use the other head I have that is good. One head is worthless, cam got down into cam journal, but the other two heads are fine.

 

Other good news is my CW 434 kit and FMF full exhaust arrived so the plan for tomorrow after work and maybe Sat if needed is to assemble one DRZ, likely the street legal one, with the 434 big bore kit, good valves and head and get it broken in to ride Sat or Sun :-)

 

Thanks for all the suggestions and input, hopefully the valves are the problem and will be easily solved, if not I will update.

If the valve face is worn to the point it is no longer sealing.. tossing in a different set of used valves is not a good solution.

 If you have a DRZ head that is serviceable, use it complete. 

 

Otherwise take a head with worn valves (not the one you hand sanded)  to a reputable shop and have them install new OEM valves, springs, seals, and cotters. 

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