Frank@Work

Some months ago my crossover pipe broke. The flange which connects to the turbo broke completely of the crossover pipe.
I bought a brand new crossover and had it modified by Lindsey Racing to make it a 3 piece crossover pipe. After app. 2500km a flange from the modified part of the crossover pipe broke.

At that point I started to suspect my aftermarket exhaust headers causing the problems. I bought a used crossover pipe and replaced my exhaust headers with stock headers.

Yesterday the flange which connects to the turbo broke again (after app. 2000km)!

I must be doing something wrong but cannot figure out what. Please help! I am going to spend another weekend on replacing the crossover pipe and hope this will be the last time.

special tool

Do you think you are running excessively high EGT? With high boost, or retarded timing?

Frank@Work

Fact is it happened a day after leaning out the AFR. I was running way too rich.

Ahmet

The only thing I can suggest is to check your balance shaft timing. I've seen it break fuel rails, accessory brackets, back out bolts, so forth. I would start by checking the upper one (drivers side).

I've done timing/balance belts on at least a dozen 944/951s, I have not seen ONE that was timed correctly, even at reputable and expensive shops.
Ahmet

tammons

My guess is it is due to thermal expansion and probably somewhat related to your headers and high heat. Turn up the boost on anything and any pipe ahead of the turbo can really grow and I mean a lot. You probably got the works so hot it expanded past the point it was designed for. I have a single turbo 928 with a very long crossover tube, all custom, from the driver side manifold to the passenger side under the bell housing and snaked through to the front of the motor where the turbo lives. Its is a very long tube, but that was the only option without major accessory relocation. I had a lot of problems with my first crossover connection setup. Unfortunately it reared its ugly head during a trip, but I was able to limp home, wrenching all the way. I ended up re-working that setup with semi custom exhaust ball joints with spring bolts and a big expansion joint at the major hot spot. That solved all my problems and I have over 2 years on it as a daily driver. It sounds like you might have to build a custom crossover tube or at least modify one by adding another expansion joint. The joints really need to be able to move and expand a lot to keep these things from happening.

James Achard

Frank, Does your crossover pipe have any allowance for expansion/contraction? Many of the aftermarket pipes do not have a stainless bellows or braided section to allow for this.

Stainless steel moves around alot more than mild steel and in my opinion over constraining the exhaust system is going to lead to failure.

How is the flange welded on to the tube? Did they use the proper welding tecniques; filler rod, fitup, process etc? The flange should be fully welded on the ID and intermittently welded on the OD to reduce the cance of internal stress buildup which leads to cracking. Refer to AWS(American Welding Society)codes.

Cheers, James

brad-cam

It's a long shot, but also check your motor mounts. Really worn mounts will let the engine sag and puts stress on the exhaust system. My exhaust manifolds cracked all to hell due to mounts that had sagged by at least 1/2" and were run this way for some time.

A long shot, but check it out...

Flight_951

Are your wastegate brackets still installed?

Frank@Work

My wastegate brackets are stil in place. Should I remove them to give the exhaust system more free play?

I will have a look at the motor mounts and the (balance belt) timing.

Thanks!

It's going to be a long weekend!

Mike S

Is your turbo clocked properly? I'm just wondering if its twisting on the pipe a bit. Does it go together fairly easily when you bolt it on?

Frank@Work

I have just completed taking off the complete exhaust system. De nr 1 cylinder exhaust header looks way too lean (white/grey). The rest looks pretty good. I also noticed the flange on the no. 1 exhaust header is cracked!
Another thing I noticed is that the bolts on the flanges which connects the small wastegate pipe to the crossover pipe where loose. I had fastened them only two weeks ago.

The timing on the belts seems to be ok, but I will check that thoroughly tomorrow.

The turbo must be clocked correctly, because it has been on the car since it left the factory. Everything bolts up quite easily.

Frank@Work

I have found several parts to be broken/cracked!

1. The crossover flange which connects to the turbo had completely broken from the crossover pipe.
2. The flange from the no. 4 exhaust header (the one nearest to the flywheel) was cracked but still attached to the pipes.
3. The LR 3" exhaust pipe coming from the downpipe had a crack in it!!! Due to vibrations (i guess) the exhaust pipe touched the oil pan and produced a crack.

Things I am going to do about it:

1. less boost (18 --> 15 psi) to produce less heat
2. weld the exhaust header
3. I have made a dent in the exhaust pipe to get more clearance at the oil pan and will weld the crack
4. Remove the wastegate brackets
5. Re-adjust the AFR and make it richer

I hope this will do it!

Laust Pedersen

I would recommend thermally coating at least the inside of the pipes. That way the metal temperature and in particular the temperature gradient (which bends pipes) will be lowered.
As “side-effect” you will also get quicker turbo spool-up ... and a lighter wallet.

Laust

Frank@Work

That was a nice weekend. NOT!

I have ended up throwing the 3" exhaust in the bin and putting back my stock exhaust! No way I could get the 3" to fit like it should. The main problem was getting the wastegate stress free in the exhaust system.

Frank@Work

After putting back the stock exhaust and turning down the boost from 18psi to 14psi I have been driving around without problems, but still not as smooth as I liked it to be.

A tip from a fellow rennlist poster made check the lower balance shaft timing mark. It wasn't the way it should be, causing vibrations throughout the entire car. It weren't violent vibrations, but they where noticeable.

Last weekend I corrected the problem with the balance shaft and spent some time fine tuning the AFR. It is like having a whole different car!!! My Zeitronix shows a perfect AFR of 12.5:1 at WOT and the transition from cruising to WOT goes so smooth it seems like there is no turbo lag whatsoever. The car feels very smooth and sounds great.

Next weekend I will put back the 3" LR exhaust, but will put in a flexibel part in the wastegate exhaust pipe to get things lined up the way it should be. I'm pretty confident the problem with the breaking cross over pipe was due to the misaligned lower balance shaft.