Yesterday I did some shopping for a jspec engine. I tested compression on about 5 or 6 engines and there was no ones that had more than 60 psi. I guess something is wrong. I know that jspec engine are not always in good shape, but I think it's impossible there was not at least one good. Maybe I didn't did the compression test right. I put some oil in the engine, WOT, cranked with the starter. I tried with 2 different testers (not mazda tester) with removed check valve.

I tested a 13B-re which I'm very interested in and it had 0-0-0 on read rotor. When I say 0, it's 0 the needle didn't move at all. I said to myself, maybe the seals are just stuck what do you think ? What do you think ? Is it possible ?

Thanks for help!

 

How were you testing them? If they weren't on a car then you can't really check the compression at all.

 

why can't you test them with out it in the car?

 

I don't know many people that can get an engine to rotate as fast as a starter motor by hand turning it. Do you? You can do that sound test where you listen for the pssht! and see if you get all 6 bursts but I doubt you can get the same numbers as with a starter.

 

good point.

If you happen to have bruce's rotary rebuild video, he shows you how to test an engine on the crate, I think he does just like this, every half turn you should hear one pop out the exhaust port, beyond that there isn't a lot you can do but put it in the car and pray

if there's no header or manifold on the engine you can inspect the seals through the exhaust ports, kinda.

 

I plug a batterie on the starter, cause the starter and the tranny still on the engine. So the engine turn as fast as when the engine is in the car.

 

maybe turn it by hand and squirt a little oil in the each chamber?

 

To get real compression test numbers the engine needs to be at normal operating temp.

But a poor mans compression test is a anouther thing

James

 

really? I didn't know that

 

Most jspecs have a transsmission and starter on them still.

Use some jumper cables and a battery or a booster pack and you can do a compression test just like it was in a car.

I've done this a few times.

Also, on the 0-0-0 it means at least 2 of the apex seals have failed, probably all 3.

I would not buy a jspec without compression testing it...

 

Also, I've tested a jspec with 0's out of both rotors.

Are you sure your source for cranking the starter was strong enough? Maybe it wasn't turning over fast enough.

 

I did a compression test a while back on my car and got 60-60-60 on the rear rotor. The haynes manual says the compression should be around 80 psi with a tolerance of +/- 20 psi between the 6 rotor faces. that leads me to believe 60 psi is ok...for a motor with 180,000 miles on it (like mine ) A Jspec engine should be very close to 80 psi if it has as many miles as they say it does. The compression wil be slightly higher when its warm because the aluminum expands and makes the clearances tighter and you get less leakdown. Also on a side not make sure you put some kind of metal or plastic plug where the check valve was on the tester, dont use your thumb, it wont make a positive seal, and results will be less accurrate.

-E

 

No, no, no. 80-85 pounds is where you should start thinking about rebuilding. Good compression is 100+. Tolerance of 20 psi between rotor faces means if one rotor goes 95-97-60, you should be rebuilding.

 

I'm sure the source was strong.

This is not true, I asked this question a few days ago cause I was not sure and I though the samething as you. Check fc3spro.com, you will see.

What I really don't understand, it's why I didn't even get an engine with at least 80 psi. It's weird. I'm a bit discouraged right now

 

someone has other inputs ??

 

when i got my j-spec it had 0 comp on both rotors from sitting. runs great now, it was hard to start the first time though.

 

how do you get one face with compression that much lower when one weak seal would mean two sides should be low?