just finished a rebuild, now ive got problems...
 

hey all,
I just got done rebuilding the engine in my s4, and i got it back in the car today, but the problem im having is that the compression is extremely low in the front rotor, something like 25 psi. also it is having issues with starting, itll crank, but it wont catch and actually fire up. any ideas as to what might cause this?

asianguy

whats the rear rotor compression?

and the number isnt what matters. you want 3 identical pumps. like: 30/30/30 is good. but, 30/20/20 is bad... how is your coming out?

and one thing new builders will have a problem with is putting the small corner piece on the apex seals. the can easily flip around or fall out of place...

there could be many problems when rebuilding a motor if not done correctly. but to find out, you usually have to open it back up to see...

the rear rotor is at 65-65-65, and when i did the build, i triple checked that corner portion of the apex seals and they were all in correctly, the motor even turns easily by hand too so i dont think anything is jammed in between the housing and rotor either. I followed the engine overhaul instructions in a haynes manual to the letter for this too, so unless there is a f**k up there i dont know what to think...

Did you reuse anything? Compression is typically low on rebuilds. They take time to build up compression.

just reused the apex seals, and they were in almost perfect shape, everything else that could be replaced was, would the compression issue have anything to do with the inability to start?

Yes, with compression that low the engine will not start. Did you use anything to lubricate the engine internals? Try pouring some 2 cycle oil in the spark plug holes to raise the compression to get it to start. You may also have made a mistake in the assembly, which will require the engine to be dismantled. If that is the case put in new apex seals.

If you have three even bumps front and rear it will start. The low numbers will make it more difficult but the numbers will be higher once it has ran/broke in. I have had to pull a friends car behind a truck in first gear to get the engine spinning fast enough to start.
Give that a try it worked like a charm for us.

ive used 10w-40 for the engine, and its getting into the internals cause when i crank it i get oil smoke out of the exhaust. with compression i get three even bumps, but with it being that low, which seal is the most probable cause for compression issues since the apexes are in good shape? Ill try two-stroke oil and let you know how it works.

I have always liked 20w-50 but beside the point, if you have your omp hooked up you will be getting oil in the internals. What did you put on the seals when you put them in the rotors to hold them in place? I know it sounds like it shouldnt have to be done but just pull it behind something, not fast just 5-10mph and let the clutch out in first it should fire up pretty quickly, you may have to hold the gas pedal to the floor too, and it may smoke alot on first startup.

you're sure it's got fuel right?

checked the lines up to the injectors, but shouldnt there be fuel present since the oil is burning/smoking?

vasoline, crisco, or wheel bearing grease is usually spread on the plates and housings to lubricate and add compresion for start up. did you do this???

also, if your sure the apex seals are good and the corner piece didnt flip. you might have either clearenced the side seals incorrectly. or just put them in wrong...

my bet is your going to have to open it up again...

Your car is not starting so you can't assume anything. Verify that you have fuel pressure and that the lines are routed correctly. Just jumper the yellow fuel pump connector.

The OMP does not supply enough oil to lubricate the internals of a fresh rebuild if the builder did not use enough assembly lube to create compression. None of the engines we build require pull starting. Pour some 2 cycle into the combustion chamber to help raise teh compression.

The myth that fresh rebuilt engines have overly low compression (to the point where it wont start) was started by people that build crap/budget engines. Compression does raise during the break-in period, but it will never go from 30-100. Most of our engines start at 110-115 and raise to 125-130. This also means that they start right up on the first try as long as everything else has been connected properly.

1. Check if you are getting fuel
2. Check if you are getting spark
3. Check your timing
4. Try pouring 2 stroke into the engine as mentioned ^.

well the fuel pump is working, and the lines are good, still need to check the injectors, im getting a good strong spark, i tried the two stroke fluid and got no result, ill start opening it up tomorrow again since i didnt use any assembly grease on the plates and housings since it wasnt mentioned in the book and ill check the side seals, cause i had some bad luck trying to clearance them properly and that could be the problem. before i do that though, what is the best/easiest way to check the timing?

I'm wondering if you measured everything properly. Plates especially if they were not lapped. Rotor housings flaking any or rough spots near the sparkplugs? My engine builder taught me many things about rebuilding that the rebuild manuals never mention.

What book were you using? The FSM clearly shows to lube parts and housings.

Couple of things...make sure you didn't switch the fuel supply and return lines near the oil filter. Doesn't sound like your problem, but check anyway. It's messed up people many times.
Other thing - make sure you 're-stabbed' the CAS properly. Turn the engine until the yellow leading mark on the pulley is aligned with the pin on the front cover. Pull the CAS out, turn the gear so that the dot is aligned with the marking on the shaft, and put it back without letting the gear turn. Some guys take out the back cover of the CAS and mark the position to ensure it didn't mess up. Search re-stab CAS, I even made a drawing to show the gear and housing alignment detail.

pull the car it has to start

That is what I have been saying all along... if it has spark and fuel pull it to get the engine spinning faster with a little 2 stroke oil in the spark hole it WILL RUN.

And Banziii there is nothing wrong with budget builds, you sound like you are talking down to those who can't afford to pay your prices... I have seen a guy do a budget build that had nearly no compression and after I helped him get it started he broke it in easy and it had 105 psi all around. :icon_tup:

25 psi of compression is nothing,that engine will not start with that low of compression even if you dump a quart of 20w50 down the plugs,im sorry to tell you this but your engine needs to come out because there is something wrong with the build.Banzai has a good point about the myth that rebuild engines will not start easy at all,you can have some decent housings but if dont clearance the seals the correct way your compression is gonna be crappy or the other way crappy housings but all the seals are on the tight side and it will start and run fine,a decent build engine without any lube inside should put out around 90 psi of compression and it should start with the key.

the housings plates and rotors are all in pristine condition, im talking like new you cant possibly tell from the internals there were 200Kplus miles put on this engine, I was using a Haynes manual and i did lube it up with 10w40 when i reassembled it. i restuck the CAS as per santos' suggestion and still had no luck. I am almost positive now that i didnt clearance the side seals properly so im beginning the disassembly of the engine tomorrow and have new seals already on the way. it shouldnt take too long to get it put together and back in the car once they get here, maybe a day and ill post results when im done. thanks all for the help, really, if not for this id probably have taken an end wrench to it by now and done something i would have regretted.

Take your time with the side seals and try to clearance them to 002 that way you will get nice even compression to start with,50 percent of the engine compression comes from seals and the rest from the housings so if your housings and plates are in really nice shape and you build a tight engine it should start right up,again take your time and clearance everything and in the end you will get a nice strong motor.

I am not talking down to anyone. That fact is crap budget rebuilds create such low compression that they wont start. You just proved my point with your story about your "friend's" bugdet engine's miraculous recovery from no compression. So he ended up with lower compression then we start with, that's great. Even if your story is true, there is not much hope for engines with 25-30psi compression. This requires that the engine be pop started every time for it to start, that makes driving the car to break it in a bit more difficult.

The myth is rebuilt rotary engines are hard to start, when really it is only poorly rebuilt ones.

just out of curiosity, ive found an FD 13bRE engine for what can only be described as dirt cheap that was essentially ripped out of the previous car it is entirely intact, and has less than 30k miles on it. would it be plausible on a reasonable budget to put it in this FC? ive hit the search and discovered that id need to change the mounts on the engine, but what else would be entailed for the transplant?

could i use a stock FD ECU or should i get a standalone?

What kind of modifications would need to be made to the drivetrain to allow for the extra power?

I know im missing a lot on the subject, so if anyone can enlighten me im extremely interested in this project if it would be possible.

big bucks. get info in FAQ on re swaps i pretty sure...