I just got my motor back together after having it down for 6 months. The engine was rebuilt using the same rotor housings which have 35k on them. They were in good shape as the rebuild was due to coolant seal failure. The engine was put back together with new rotary aviation apex seals and overhaul kit. The side housings were not resurfaced as the builder said they were ok. I am using the 2mm 2 piece seals. The rotors, e shaft, and side housings all have 100k and are original. The rotor housings were replaced at 65k when the motor went down for it's first coolant seal failure due to pitting in the rotor housing which compromised the coolant o-ring. I rebuilt at that time using the atkins 2 piece 2mm seals.

With the motor finally up and running, I decided to get compression test to make sure there are no major problems with the engine before putting miles on the car. This will also give a base line for comparrison later when I recheck after breakin.

The results using the mazda digital compression tester are as follows. The engine was at operating temp for the test. I have 175 miles when tested.

Front rotor 6.5/7.5/7.5 277 rpm
rear rotor 7.1/7.5/7.3 274 rpm

I understand that the RA seals take a while to breakin and the overall values will get better. My concern is with the low 6.5 on the front rotor. It is out of sync with the other two compression faces. It is a whole point lower.

I am also getting an uneven idle and poor vacuum of only 10 inches. This could be the porting. The car backfires a bit and seems to have developed a bad miss that started just after the compression test. If I rev the engine in nuetral to around 3000 rpm it is not smooth but breaks up. I watch the wideband and get around 12.5 afr. If I add or subtract fuel, nothing changes. The car stll runs rough as if its missing and wideband readings stay the same. If i'm driving or idleing, and make fuel changes, they show up on the wideband, but when just free reving the motor, and pulling fuel the miss doesn't change and the wideband doesn't show the car getting any leaner. I can see the duty cycles getting lower though. I am confused about this.


I plan to recheck the compression at 1500 and see if it improves/changes. Any input would be great at this point. Due to all the damn hurricanes, I have had very few weekends to work on the car.

Mike

 

well I fixed the rough idle today. turns out I did not have the ground strap at the back of the intake manifold installed. There are a couple of grounds that come from the wiring harness which bolt onto the rear UIM bolt. The ground strap at this same point must help distribute the gounds to the chasis. As soon as I hooked it up the idle became nice and steady.

One problem down 10 to go. I will see how it drives tomorrow.

Mike

 

sticky side seal might do that.

 

i have rough idle at cold start too on my maz. reman with 100miles on it. After its warm, with AC on, the idle would jump up n down also and eventually shuts down the motor...

 

it has been my experience that aggressive streetported motors pull 14 in kg. assuming you are pulling 10 you either have a vacuum leak or a cornerseal/sideseal problem.

the easiest way to test for a vacuum leak is to spray carb cleaner, brake cleaner or something similar around your engine while it idles. if you have a leak the idle will change.

as to your low rotor, cross your fingers and hope it comes around w some additional miles.

good luck,

howard coleman

 

You will never know how a motor is going to be unless you break it in. A fresh motor almost all the time has problems running because of the low comp. If you have 700miles on the motor and it's still having problems, then you should be worried. Break in the motor for 700miles and see what happens.

 

side seal or corner seal was my thought also. I didn't know what to expect for vacuum but thought that 10 was a bit low.

When i first started the motor, I got a lot of blow by into the crankcase. It caused the oil to force past the piston ring seal in the turbine housing and dump oil out the downpipe. At first I thought it was a bad turbo but we ruled it down to excess pressure in the crankcase. I had accidently capped both vents on the oil filler neck and this left the pressure no where to go but out the turbine side of the turbo. The problem is that this occured while just reving 1500 rpm trying to keep the motor running after cranking her over for the first time. I do not think that I should have created so much pressure in the crankcase by running it for only 2-3 minuites on the lift. I am also getting a lot of condinsation under the oil filler cap but have read that this could be normal.

The plan is to break her in for about 1500 miles and then retest to see how she looks. I am going to change the oil at 500, 1000, and 1500 miles to have it tested. If there is a lot of fuel in the oil and the percentage does not go down then this will help be an indicator along with the new compression test.

Mike

 

as long as it runs fine just leave it in there. that compression is decent

 

Run it for a while. Compression is acceptable (approx. 7.0) and you are within the factory reccommended differential between chambers (1.5 kgf/cm2).
10 vacuum is low for a fully broken in engine but you also may have a small leak somewhere.

 

cool, my mechanic said that he didn't like anything over 0.5 differential. I saw in the manual that it stated 1.5 and was a little more relieved. I am going to try and hunt for a vacuum leak, but there isn't much left to be able to leak. Everything has been blocked off.

mike

 

There seems that you have some problems after the rebuild but I would not worry that much on the bad compression test results. My engine was rebuilt as well by two specilist it did not give me any trouble at all except for some extra backfireing which was reduced nearly to zero by sealing both exhust gaskits.

When I proposed a compression test to my specilist both said that till the enging was in a running in state the compression test would be useless since the engine was still settleing down.

 

it isn't a super motor but its acceptable. just drive it

 

"it isn't a super motor but its acceptable. just drive it"

well, this motor is for my new gt40r turbo. I made 400rwhp with my old motor on my rx6b at 14 psi. I am hoping to hit around 430 at the same boost and plan on running higher boost with water/methanol. This is not the best way to start. Obviously, I need to drive it more before anything concrete can be determined so hopefully things will work themselves out.


There is one other problem that I am trying to deal with. I have been able to get the car to idle fine and drive fine. The AFR's are good and my lean cruise cells are around 13.0-13.8. I have the idle running around 12.5-12.8. I have only been driving around under 4k and no boost. I have been working on tuning these cells. I get no bucking and the car accelerates smoothly. But here is the weird thing. If I am cruising at 2500 rpm lets say all is fine the car has no miss and drives smooth. But, if I am at a stop and rev the car to 2500 rpm in nuetral or with the clutch in, the car misses badly and runs rough as though its got bad plugs and won't clean up. The AFR's at this point are 11.7. With the power fc I go to the test/inj screen and start pulling fuel to lean it out. Nothing happens. I can cut the fuel in half by putting in .500 in the test section and the afr's remain 11.7 and the car sounds the same. If I let off the gas the car dies immediately. It's almost seems as though the car is getting fuel on its own but it runs fine if actually driving at 2500 rpm and idles fine. If I add fuel in these other situations it gets richer, and if I take fuel out it gets leaner. But if just free reving the engine, it sounds like **** and no matter how much fuel I pull the o2's stay the same and the car never cleans up. If I add fuel, the afr's stay the same but the car sounds like it's getting more labored so something is going on. My vacuum is also low as mentioned above, 11in.

Anybody have any clue why this is. My injectors are 775 pri and 1200 sec. The Power fc is set up right. I have new o rings but reused the insulators. The primary injectors were just upgraded while the engine was down and the 1200's were sent in for cleaning at the same time. The primarys are just bored out 550's.

mike