How much can a bad oil seal effect compression

[toad772]

How much can a leaky oil seal effect compression.

[mopar4u]

if your talking about crankshaft seals on a 2 stroke, you won't see a difference in compression. Compression only checks piston rings, cylinder condition and head gasket.

To properly check if an oil seal is bad you need to perform a leak down test. This test is very cumbersome on a 2 stroke. There are other tests which people claim work to test crank seals which I have little to no faith in. One is spraying carb cleaner around the suspect seal while the engine is running and listen for a change in rpm. Personally I think the seal has to be real bad for this to work.

If you do have a bad crank seal your engine will run lean . You may notice eratic or high idle, bogging, white looking spark plug, gas/oil seapage from the seal area.

[toad772]

I mean oil seals not crank case seal. If they do not effect compression then I guess something is bad in my top end. Will this http://cgi.ebay.com/ebaymotors/REPLACEM ... arQ5fParts fit my 86 Honda aero50?


Oh and my engine does not run I am working on getting it running has very little compression.

[evilone]

That linked piston fits your motor. The oil seals will not affect compression, most likely rings are bad.

[toad772]

That linked piston fits your motor. The oil seals will not affect compression, most likely rings are bad.

Well time to take that head off then.

[evilone]

Good idea, hopefully you won't need a piston.

[toad772]

Good idea, hopefully you won't need a piston.

Fingers crossed.

[Bear45-70]

if your talking about crankshaft seals on a 2 stroke, you won't see a difference in compression. Compression only checks piston rings, cylinder condition and head gasket.

To properly check if an oil seal is bad you need to perform a leak down test. This test is very cumbersome on a 2 stroke. There are other tests which people claim work to test crank seals which I have little to no faith in. One is spraying carb cleaner around the suspect seal while the engine is running and listen for a change in rpm. Personally I think the seal has to be real bad for this to work.

If you do have a bad crank seal your engine will run lean . You may notice eratic or high idle, bogging, white looking spark plug, gas/oil seapage from the seal area.

You need to bone up on your 2 stroke theory. A 2 stroke pressurize the mixture in the crankcase and then feed the mixture into the cylinder UNDER PRESSURE. So a bad crank seal will effect compression. How much depends on how bad the seal is, but it will lower it for sure.

You also do not need to preform a leak down test to check the case seals, a leak down test only checks the cylinder and rings. You pressure and vacuum test a two stroke crankcase to check the seals. You car guys need to stop applying 4 stroke stuff to these 2 strokes.

[mopar4u]

if your talking about crankshaft seals on a 2 stroke, you won't see a difference in compression. Compression only checks piston rings, cylinder condition and head gasket.

To properly check if an oil seal is bad you need to perform a leak down test. This test is very cumbersome on a 2 stroke. There are other tests which people claim work to test crank seals which I have little to no faith in. One is spraying carb cleaner around the suspect seal while the engine is running and listen for a change in rpm. Personally I think the seal has to be real bad for this to work.

If you do have a bad crank seal your engine will run lean . You may notice eratic or high idle, bogging, white looking spark plug, gas/oil seapage from the seal area.

You need to bone up on your 2 stroke theory. A 2 stroke pressurize the mixture in the crankcase and then feed the mixture into the cylinder UNDER PRESSURE. So a bad crank seal will effect compression. How much depends on how bad the seal is, but it will lower it for sure.

You also do not need to preform a leak down test to check the case seals, a leak down test only checks the cylinder and rings. You pressure and vacuum test a two stroke crankcase to check the seals. You car guys need to stop applying 4 stroke stuff to these 2 strokes.

Very rarely does a bad seal show up on a compression test. Compression tests are done to check the top end.
I'm not a car guy, I work and ride on snowmobiles all winter.
Perform a leakdown test/pressure test (whatever you prefer to call it) from the intake, not from the spark plug hole. Block off the exhaust. http://www.duncanracing.com/TechCenter/ ... sstest.pdf

[Bear45-70]

Very rarely does a bad seal show up on a compression test. Compression tests are done to check the top end.
I'm not a car guy, I work and ride on snowmobiles all winter.
Perform a leakdown test/pressure test (whatever you prefer to call it) from the intake, not from the spark plug hole. Block off the exhaust. http://www.duncanracing.com/TechCenter/ ... sstest.pdf

I beg to differ with you. After 25 years as a 2 stoke mechanic, I can tell you that a bad crank seal sure as * will show up on a compression test. But then having been a factory certified 2 stroke mechanic makes my experience null and void according to you. I was doing crankcase vacuum and pressure test 20+ years ago, what were you doing?

[toad772]

Well I will be taking them engine off the scooter tomorrow and bringing it down onto the work bench so I can work on it easier.

[toad772]

The piston is toast and I don't know about the cylinder it doesn't have any gouges out of it but it does have like a bump on it in one spot looking form the bottom or the top you can see it sticking up a little bit. Will post pics later.

[toad772]

Making new thread with pics

[evilone]

A 2 stroke pressurize the mixture in the crankcase and then feed the mixture into the cylinder UNDER PRESSURE. So a bad crank seal will effect compression. How much depends on how bad the seal is, but it will lower it for sure.

Makes sense.