I'm installing a stock exhaust manifold and 99 twins with new OE gaskets. What, if anything, does everyone here do to clean up the mating surfaces (on the rotor housings, each side of the exhaust manifold, each side of the turbo manifold, and on the downpipe) prior to reassembling these parts? I want to do everything I can to avoid exhaust leaks. This is being done with the engine in the car.

 

Usually the mating surfaces are good to go as is, put the gaskets on and torque it down. If you have spots of carbon build up on the mating surfaces, CRC Spray on Gasket Stripper will remove it with a spray on and wipe clean with paper towel.

If your new gaskets are Multi Layered Steel (MLS), there's not much of a chance for leakage.

Also, putting some copper anti-sieze on the stud threads should help save them if you ever need to remove it in future.

 

Thanks, Axton.

Anyone else have input on this? I know there are plenty of folks here who have taken these cars apart and put them back together a million times.

 

Nothing really special here. Brake clean and maybe a wire brush and/or scotchbrite pad. It doesn't have to LOOK perfect, just has to be flat. Discoloration is fine, the gasket doesn't care about the color. Big thing is just any carbon that could be there.

The stock gaskets are multiple layer stainless so they don't leave junk behind like a paper gasket.

NEVER put any sealant on exhaust gaskets - no dressing, RTV, etc. If you have 2 flat mating surfaces and the stock gasket it will seal properly.

Also look at the turbine housing on the turbos - if it is cracked, you don't want any cracks to go under the gasket, that will blow it out. Some cracking is fine and unavoidable and really doesn't hurt anything.

Dale

 

You mean something like this?

When I gave my turbos to a shop (that rebuilds turbos) to port my wastegate this is what they did to the mating surfaces, not sure if this is by the book or not...and have not installed them yet so I can't personally comment on whether there are any exhaust leaks or not...

 

^Looks like it was put on a belt sander.

I second what the others said. There’s usually a hash-mark pattern left by the old gasket, no big deal. I think I checked the surfaces with a razor blade scraper and if the scraper didn’t catch on anything I kept going.

In addition to the hi-temp anti seize I’d also suggest chasing the threads with a tap or die the threads too. Might be kind of a pita with it in the car, but it’ll give you a more accurate torque.

 

The belt sander method can work, you do have to be careful that you don't take too much off. A few millimeters doesn't seem like much but there's a lot of stuff that's positioned just so to line up with the turbos - if you throw one thing off it can impact other things for fit.

I had my compressor housings off by literally a few degrees and the Y-pipe wouldn't sit flat and the crossover pipe would hit the water neck.

Dale

 

I remember they told me they didn’t grind much of the surface off to avoid messing up any positioning later on.

I can’t confirm whether there are any fitment issues yet. If I ever install them I will update the thread here.

cheers

 

Yeah that looks reasonable but just throwing that caveat out there

Dale