12abridgeport

I noticed that after about four 1/4 mile passes it becomes very hard to start the car. So i borrowed a compression tester and checked the compression on a cold engine, it was 83 and 85 psi (it used to be over 90 but i don't know if plenum made it drop), then i also checked the compression after running the car for awhile (just before half way mark on temp gauge), it was 60 and 55 psi .

Does anyone know if it's normal on a brigeport??

Also would that affect my timing or tune up in general? I noticed that my timing gets too advanced sometimes, i don't know if that might be becauese of that or because i don't have msd boxes or a welded dizzy.

Any help greately appreciated

Wankelguy

With compression that low, you're lucky the thing runs at all. It is normal for a cold rotary to have a bit higher compression, though.

12abridgeport

Does it mean i'm loosing compression on my engine?

Onece it is running it feels pretty strong. But i do feel like my top end went down, i thought that was just the tune up.

Jeff20B

iTrader: (13)

Mine is hard to start when warm too. Maybe that's why Mazda started installing a hot start assist on the Nikki carbs?

1st to 3rd

It's normal for the compression readings to be higher when the engine is cold. Even on a healthy engine. Mazda recommeds to perform the compression test at normal operating temp.
A sign of an engine with low compression is trouble starting hot. Your problem could be a number of things, but a dying engine is a strong possibility.

12abridgeport

Would anyone know what could have caused such a premature engine wear, i probably have less than 2k on the engine after rebuild. I've had all the seals replaced except for oil seals and bearings. Took about 500 miles to break in but it did hit about 7k a couple times in neutral. After that it has been nothing but a track car, i'm pretty sure i've hit almost 11k a few times (i only have a stock tach). Oh yeah, my pre-mix is on all the way too.

I know i pushed the engine but shouldn't it still last a little bit longer than that?? Anyone have any suggestions?

rotor vs. piston

It could be simply a cloged cat. converter (if you have one on the car) But logic would say you should have higher compression when the engine is warm.

12abridgeport

It's defenetly not the converter, i've got a straigh 2.5 inch exhaust.

I'm at the point right now when i have a real big urge to just get rid of the car and start over again. Maybe get something that already has a turbo. FD would be very nice but way out of my reach, TurboII is hard to find....maybe a DSM

Wankelguy

Since when does a clogged cat affect the compression?
And I'm eager to hear what "logic" says that a ROTARY engine should have higher compression when it's warm.

Wankelguy

Lousy rebuild and/or over-revving is the first thing that comes to my mind. JMO.

DriveFast7

iTrader: (1)

low compression is low compression.........

time to crack it open.

12abridgeport

On a rotary, if i used new seals and the engine cranks and runs, how is it possible to have a lousy rebuild?

I just can't see what could be assembled wrong if it cranks.

When putting the factory apex seals, i put the little triangular pieces downwards for easier installation, would that make a difference?

Wankelguy

Did you use new apex seal springs?
What was the condition of the rotor housings?
Did you do any oil mods?
Did you clearance the rotors for high rpm use?
Did you balance the rotating assembly?
I'm not trying to start any trouble, but these are all things that influence the quality of a rebuild. Rotary engines are real popular because you can get a lot of horsepower pretty easily, but building a motor that will also LAST takes some doing. I know some complete IDIOTS who can build a 300 hp rotary, but the damn things won't last. Sorry, but that's just my experience talking.

12abridgeport

Wankelguy, i see what you are saying. This was my first time rebuilding the engine so i'm still learning. And the only way to do that is to keep trying.

I did use all new springs including apex seal springs. Rotor housings and side housings are in pretty good condition, they only have like 50k on them. I didn't have any oil mods, clearanceing, or balancing.
Do you think that could explain the premature engine wear?

Also if my seals did wear out, how come the engine doesn't smoke even when i rev it up? And the exhaust feels really strong?

Thanks in advance

thecause17

Yeah, I could see that with a piston engine. Usually there's enough heat expansion to make the compression look more normal after warm-up. I saw it happen on a turbo Integra once.....guy beat on it hard one night, drove it home, started it the next day and found out it had no compression...the fact that the engine was hot the night before was pretty much the only thing that kept it going.

Not sure it if would apply to rotaries though....

12abridgeport

I think in rotaries it has an opposite effect, at least from my experience. I was driving it home one night after the races and it stalled out on me. I couldn't get it to start until the engine cooled down a little bit.

When it is totally cold though, it starts up like an angel.

Wankelguy

REVHED

11000rpm is way too much with the stock seals not to mention power would fall off way before then.

Also, I wonder if flooding could have anything to do with low readings when hot. Is it hard to start normally?

Sterling

Logic tells me that cool mixture is more dense than warm mixture, and consequently, compression should be higher when cool.
However, I donot think that is the bulk of your problem, though I believe it's part of it. The other part of it I'm pegging as your oil. Try a heavier wieght, and see what happens.

12abridgeport

Yeah, i know 11k is a lot, i was just experimenting

I already use Castrol 20W50 and add some STP oil treatment every oil change which is like once a month.

I guess i should try the Amsoil Power Foam as Wankeguy said, hopefully it's not too expensive.

KYPREO

at 11,000rpm its not just seals, you've got harmonics problems with the stationary gears (tendency to crack due to the gear profile inducing harmonics), and the engine bearings. Then there's the seals, the balancing, oil supply (factory wet sump foaming up oil at high rpm)....list goes on.

Not many rotaries can actually withstand a handful of attempts at 11,000rpm.

BRealistic

Hmmm. I don't think you broke the engine in properly. Fresh rebuilds with old housing take several miles to build compression- to allow the new apex seals to wear to the housing surface. I though 1500-2000 miles was the number to reach BEFORE revving the engine hard?

12abridgeport

I guess 11k rpms, lack of mods, and a bad break in are all the factors of my pre-mature engine wear.

I think i'm going to street port now and not rev higher than 8k.

At least now i know the things i need to do if i wanted to bridge again and rev real high.

Does anyone know if it's expensive to do balancing, rotor clearanceing, and oil mods? And if i have to do that for a street port?

Wankelguy

A good rotary engine builder can balance your rotating assembly for you, and it shouldn't be too expensive. Call Rob Golden at Pineapple Racing in Portland, OR and see what he would charge. If you go with a street port you don't really need to go with clearancing, oil mods, or hardened stationary gears as long as you keep it below about 8k. But I would definitely get the rotating assembly balanced with the flywheel you're going to use. And I agree with the previous poster about the length of break-in.

12abridgeport

Alright, i pretty much have all my questions answered now. Thanks everyone for their responses.

Hopefully i'll be back soon with my street port and i might even have it last long enough to save up for NOS.