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Previous Next Up Topic Engines / Subbug - Subaru Power / Monel Exhaust Bolts (6588 hits)
By @Jeff GS Date 2010-01-21 22:25
This is a reply of sorts to Tom about his choice of running nickel/copper (aka: Monel) bolts in the exhaust system - and in particular connecting turbo to header.
I was looking for something other than steel for corrosion resistance and easier servicing down the road (like when I upgrade to that STI turbo....  :-)  ).
I also wanted something that wouldn't turn to rust in the first few months of operation.  I purchased some metric ARP SS bolts to use for this - but then realized the one bolt hole below the turbo outlet doesn't have any room to use anything other than a hex head fastener in that position.  No way to get a wrench on the 12-point!

So Tom - I've decided to switch to the Monel 400 hex head bolts for bolting turbo to header.  These are well matched to the expansion characteristics of steel, but with high temperature and corrosion resistance of stainless.  There was just one thing I didn't like about them - I can only find them in SAE thread sizes.  The closest is 3/8" (vs. 10mm) - which is only about 0.015" difference.  Normally that wouldn't be too big a deal - but the bolts align the turbo with header, and you don't want any off-set/blockage where the two meet.  Add in the bolt hole clearance and one could potentially have some power robbing mis-alignment during assembly.

What was needed is some way to "bush" the 3/8" bolts to fill the holes.  I considered various tube type bushings, but trying to make something such thin wall - out of stainless steel would be problematic.  Then it dawned on me - which not use shim stock!  I located some 0.005" thick stock - which can be cut with good scissors.  A couple loops around a bolt formed a great shim to take up the slack - like an alignment bushing!  Problem solved!

I do plan to keep the outlet side bolts the original ARP SS, I still think they may work OK when torqued down well.

Man, I'm going stir-crazy trying to figure out things to figure out while I can't do any physical work on the buggy!

By Tom & Kathleen I 639 Date 2010-01-22 13:34
You are way too anal!  LOL  I just lined up the flanges and bolted it down.  We are not looking for the last bit of power the engine can put out.  It is wicked fast just the way it is, and if you want more power, up the boost.  But, by being as anal as you are, it is making you do a fantastic job on that car.  Tom
Tom & Kathleen Manxter #16, Kick-Out SS #16 & FiberFab Buggy
Manx Club #1030, CVA, RBC, SCCA
By @Jeff GS Date 2010-01-22 22:23
Hey Tom - just going stir crazy until I can actually do an "real" work on the car, when it warms up a bit!

So one question - did you do anything to "lock" the fastener and keep it from loosening?  I'm planning on the bolts and nuts (about $15 for 3 sets - sheesh!), debating the lock washers, another $12.  All this for 3 lousy bolts!

By Jay H (X-20) (ManxVair CC) Date 2010-01-22 22:59
Do they offer cross-drilled nuts for safety wire? You could drill them yourself with a jig.

I had ss lock washers on mine initially which may have failed from heating/cooling cycles. Two of the three nuts loosened completely off. Thankfully, I installed the bolts head up, so they remained in the flange holding alignment at a minimum. If my current fix doesn't hold, I'm going to safety wire them.

By Tom & Kathleen I 639 Date 2010-01-23 02:08
Jeff - I just used regular nuts with SS washers with the bolt heads up as Jay mentioned.  I had to buy 4 nuts & bolts for the Garret T3/T4 so it was more like $25.  I checked them at the end of this season, and still tight.  I even used never sieze on the threads.  Tom
Tom & Kathleen Manxter #16, Kick-Out SS #16 & FiberFab Buggy
Manx Club #1030, CVA, RBC, SCCA
By Charles W 2165 Date 2010-05-06 18:48
Nickel high temp never sieze. Also forever we have used brass nuts to stop siezing on exhaust studs.
By @Jeff GS Date 2010-05-07 18:05

Where do you find the copper coated nuts that fit the thread on the exhaust studs (at the heads)?  I could not find any for that thread pitch.  I bought some new ones from Subaru, but they appear to be standard steel and are not copper coated.

Previous Next Up Topic Engines / Subbug - Subaru Power / Monel Exhaust Bolts (6588 hits)

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