PZ500 Compression check

Old Thumper

Old Thumper

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Nov 9, 2005
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Location
Nottingham, NH
I just did a compression check on my wifes 2001 PZ500. Sled has 6000 miles on it. The engine is cold, and has not run since I fogged it in the spring. I got 145 PSI on both cylinders. I had not been able to find any specs on what the compression should be, but I was expecting to see around 125.

145 seems REALLY good. Maybe the fogging oil in the rings is bumping it up. If the engine is tested hot, does the compression typically go up or down? :dunno:

Does anyone have the specs on what the compression should be?

This is the first time I have checked it - just got the test kit.
 
You can bet on that it's the fogging oil raising it,thats pretty high.

do it hot and wide open throttle 5-6 good pulls..
 
Carbon build-up will also raise the compression.

You should probably replace rings anyway. So cleaning the carbon off is part of the job.
 
Ding said:
Carbon build-up will also raise the compression.

You should probably replace rings anyway. So cleaning the carbon off is part of the job.
Click to expand...

OK - so let's assume the high reading is due to fogging oil in the rings. If I re-check after running the engine, and I get a good healthy compression in both cylinders, why do you say I should replace rings anyway?
:dunno:
 
prolly cause the high mileage, i like to do mine every 3000 miles just preventative maintenance allot cheaper then a full rebuild cause u threw a ring.
 
Thats nothing for mileage on the phazer style motor, its fine for quite some time, no need to even go near that motor!

Let us know what your compression is after you have did what daman has recomended. Interested to see if its like what mine is at 20 000kms, lol
 
I agree with YAMAHAHAMMER485, due the compression check after she is run and if it is good......which it probally will be just leave.
Just a note torque those heads very important on that motor.
 
blkmax600 said:
I agree with YAMAHAHAMMER485, due the compression check after she is run and if it is good......which it probally will be just leave.
Just a note torque those heads very important on that motor.
Click to expand...

Back off and re-tighten, or just confirm that they are still tight to torque spec?


I will re-post after running and re-checking compression, but it won't happen for a couple of weeks. Going away for a week and won't have the sled back together till after I get back (I have the skid out for new bushings / bearings)
 
Rings are a wear item. With that many miles they have worn down to the point that the pistons are rocking more than they should. Also the ring end gap is likely larger than it should be. At some point the pistons will begin to slap the cylinder walls and if continued to run will cause damage. They are inexpensive and extremely easy to replace on an air-cooled engine.

I don't see any reason to just run it until it breaks, because you have no control over when that will happen. Rings wear and will break at some point. It may be at 6000, 8000, 10000, or even 15000 miles, but they will break. Better to plan the down time than to roll the dice.

Worn rings that continue to run allow the pistons to wear much faster as well. The best cost-per-mile approach is to replace rings every 3000-5000 miles and pistons whenever out of spec. This usually results in the most mileage out of the pistons as well as the rest of the engine.

It also allows you to clean the carbon buildup off.
 
To check for piston wear just pull the carbs and reed valves as well as the exhaust y pipe and look in while turning the crank, I bet they look just fine. But if you feel better a set of rings are cheap insurance to keep that engine bullet proof.

Just check the torque no need to loosen off.
 
blkmax600 said:
I agree with YAMAHAHAMMER485, due the compression check after she is run and if it is good......which it probally will be just leave.
Just a note torque those heads very important on that motor.
Click to expand...

Good tip - they did need tightening
Thanks Blkmax ;)!
 
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