[Trendkiller]

Hi Guys,

I know a compression check is pretty easy to do but I have a few questions about the procedure.

Can a compression check be carried out with the engine "out of" the frame?
Can it be done safely with the oil drained? would that be accurate?

I would guess, but thought I would ask anyways...

Thanks,

Kelsey

 

[denzee]

In your situation a leak down test would be better because you don't have to spin the engine over. It's more accurate anyways because it tell you exactly where your loss is going, if you have any.

Basically it pressurises each cylinder separately through the spark plug hole and monitors how much leakage, in a percentage, that is leaking by the rings or valves.

If you can't get the tester then you are probably best off taking your engine to a shop for proper testing. The results will give you a real health report on your motor.

 

[bladeracer]

Hi Guys,

I know a compression check is pretty easy to do but I have a few questions about the procedure.

Can a compression check be carried out with the engine "out of" the frame?
Can it be done safely with the oil drained? would that be accurate?

I would guess, but thought I would ask anyways...

Thanks,

Kelsey

The engine can be anywhere, it just needs a starter motor hooked up to a battery to turn it over.
I wouldn't recommend doing it without oil but it probably won't harm it. You'd expect slightly higher readings though due to the reduced drag.
You must have all the plugs removed and the throttle plates wide open for consistant measurements.

 

[denzee]

Maybe we should ask first if you suspect a problem or just curious. If you do have a problem, you'll still need to know basically if the pressure loss is into the crankcase via piston rings and cylinder or a burnt or out of adjustment valve. One is a lot easier to repair than the other. That would be difficult with just a compression test. If you are just curious, a standard compression test will work fine. IMO

 

[RICK-ITFC]

correct me if i am wrong, but i would have said you will get a lower compression reading without oil, with oil there will be a better seal between the rings and oil scraper ring.:idunno:

 

[Trendkiller]

Maybe we should ask first if you suspect a problem or just curious. If you do have a problem, you'll still need to know basically if the pressure loss is into the crankcase via piston rings and cylinder or a burnt or out of adjustment valve. One is a lot easier to repair than the other. That would be difficult with just a compression test. If you are just curious, a standard compression test will work fine. IMO

Just checking since I will have the motor out to replace some tranny components, I thought I should check the top end out just in case.

Thanks for your input!

 

[Trendkiller]

The engine can be anywhere, it just needs a starter motor hooked up to a battery to turn it over.
I wouldn't recommend doing it without oil but it probably won't harm it. You'd expect slightly higher readings though due to the reduced drag.
You must have all the plugs removed and the throttle plates wide open for consistant measurements.

Ya I thought it would be a bad idea, but couldn't find a thread about it.
I thought someone might have done it on a motor they were buying...but even then it would probably have some oil in it...

Thanks Bladeracer!

 

[bladeracer]

correct me if i am wrong, but i would have said you will get a lower compression reading without oil, with oil there will be a better seal between the rings and oil scraper ring.:idunno:

If it's an engine that's been sitting for a while that might be true, but if the engine is that dry you should put some oil into the cylinders before you turn it over anyway.
If you do a dry test followed by a wet test (by putting some oil in the cylinders to improve ring seal), a significant increase in measurements indicates worn rings. If there's little difference then the rings are probably good. If you have some very low measurements and a wet test makes little difference then you have a valve or gasket problem.

I forgot to mention earlier, you also need to take measurements from the same number of turns of the engine. I normally work on six revolutions.

 

[bladeracer]

Ya I thought it would be a bad idea, but couldn't find a thread about it.
I thought someone might have done it on a motor they were buying...but even then it would probably have some oil in it...

Thanks Bladeracer!

If you're going to open up an engine you would normally run a compression test before pulling it out to determine if it's worth doing the topend while you have it apart.

 

[Trendkiller]

Ya the top end was an after thought, live and learn I guess

 

[bladeracer]

Ya the top end was an after thought, live and learn I guess

That's the best way to learn
I learn most things the hard way myself

 

[Trendkiller]

That's the best way to learn
I learn most things the hard way myself

this is my first time going this deep so I'll be learning a lot!
Its funny how so much of it is obvious if you know, but not so when your trying to figure it all out.

Thanks again

Kelsey

 

[bladeracer]

this is my first time going this deep so I'll be learning a lot!
Its funny how so much of it is obvious if you know, but not so when your trying to figure it all out.

I know!
I'm a hopeless teacher and I think it's because I can't step back in time and recall what it was like approaching something before I actually understood what I was doing.
I wish forums like this one were around when I was staring out, I'd be decades ahead of where I am now

 

[Trendkiller]

I know!
I'm a hopeless teacher and I think it's because I can't step back in time and recall what it was like approaching something before I actually understood what I was doing.
I wish forums like this one were around when I was staring out, I'd be decades ahead of where I am now

Ya I know what you mean, I have been surfing this forum for awhile now, but don't have many posts because most of what I need to find out has already been discussed, and if it hasn't I'm not likely to be the one to chime in with the answer.

Its guys like yourself that really help us newbies out and really make these forums valuable.

By the way, have you split the crankcase on a 929?

 

[bladeracer]

Ya I know what you mean, I have been surfing this forum for awhile now, but don't have many posts because most of what I need to find out has already been discussed, and if it hasn't I'm not likely to be the one to chime in with the answer.

Its guys like yourself that really help us newbies out and really make these forums valuable.

By the way, have you split the crankcase on a 929?

No but I have a 954 engine completely stripped.
What did you want to know?

 

[Trendkiller]

Well, I am going step by step using the Haynes manual as well as the Honda service manual. But I am a bit confused on what exactly needs to be removed from the crankcase before I separate it, considering that I am only going to be working on the mainshaft, countershaft and shift drum. The Haynes manual states that the Oil cooler must come off, and maybe the starter motor. The Honda Manual says the starter must come off. I just figured I would figure it out as I was going, but I would really rather know before hand...I'm that type of person.

Do the camshafts need to come out to remove the timing chain from the timing rotor?
does the oil cooler need to be removed?
does the starter motor need to be removed?
Do I need to remove the sump or can I just take the lower crankcase with the sump still in situ? Oh wait, I see the sump has to come off to remove the oil pump...so I guess I do.....

 

[bladeracer]

Well, I am going step by step using the Haynes manual as well as the Honda service manual. But I am a bit confused on what exactly needs to be removed from the crankcase before I separate it, considering that I am only going to be working on the mainshaft, countershaft and shift drum. The Haynes manual states that the Oil cooler must come off, and maybe the starter motor. The Honda Manual says the starter must come off. I just figured I would figure it out as I was going, but I would really rather know before hand...I'm that type of person.

Do the camshafts need to come out to remove the timing chain from the timing rotor?
does the oil cooler need to be removed?
does the starter motor need to be removed?
Do I need to remove the sump or can I just take the lower crankcase with the sump still in situ? Oh wait, I see the sump has to come off to remove the oil pump...so I guess I do.....

Camshafts can stay in since you don't need to remove the timing rotor.
I can't see any need to remove the oil cooler but it can make it easier to get to some of the case bolts.
And I can't see any reason to pull the the starter motor either.
You will need to remove the sump to reach the main bearing bolts.
No need to remove the alternator rotor either.

 

[Trendkiller]

Isn't the timing rotor shaft in the lower half? If so, I would need to at least get the timing chain off...
I spoke to a mechanic with 30 years experience and he said you just flip the motor over and open it up....obviously over simplified...but he didn't say anything about the cams either....I really hope you are right!

Cams seem like a pain in the ass....When I checked my valve clearances I tried removing the cam holders and with all the bolts removed they were twisted (the holders) and wouldn't budge...

Ya I see some of the case bolts will be quite difficult with the oil cooler in the way....I guess the book is right!

 

[bladeracer]

Isn't the timing rotor shaft in the lower half? If so, I would need to at least get the timing chain off...
I spoke to a mechanic with 30 years experience and he said you just flip the motor over and open it up....obviously over simplified...but he didn't say anything about the cams either....I really hope you are right!

Cams seem like a pain in the ass....When I checked my valve clearances I tried removing the cam holders and with all the bolts removed they were twisted (the holders) and wouldn't budge...

Ya I see some of the case bolts will be quite difficult with the oil cooler in the way....I guess the book is right!

The timing rotor is on the end of the crank which stays in the upper case half.
You need to release the cam holder bolts sequentially and keep tapping the cam holders so they come up with the bolts. You don't want the cam holders to stay down on the head when all the bolts are out.

 

[unfetteredmight]

Also there are two dowels per holder and that's where you'll meet your resistance if your having trouble getting those holders to come up. Use something plastic to gently pry so as to not slip and scratch a cam lobe. Make sure they come up evenly, I suspect that they could break easily if too much stress is applied.