Mid- Engine Modified Sports

[floydjer]

top notch work Neil. pun intended.

[manta22]

I just ran into an interesting problem- while I was bolting on my newly made rear body brackets, I noticed that the left exhaust header was a little loose. I thought that I had torqued the bolts but maybe I hadn't, so I tried to tighten the bolts that fasten the header flange to the head. No dice, they were tight! I found that the bolts were bottomed in the head. These are new ARP 3/8" UNC bolts with a 1.00" grip length and an ARP 0.050" thick washer.

Odd- has anyone run into this before? The heads are Dart aluminum heads. I added two 0.063" stainless washers as spacers and now it seats properly. Strange! Both L & R header bolts were bottomed. PITA 

Regards, Neil  Tucson, AZ

[Stan Back]

"ARP 0.050" thick washer"

I'd call that a thin washer.  Were the bolts specified for your heads with the flange you're using?

[wobblywalrus]

Neil, most of the time on bikes threaded studs are put in the holes near the manifolds.  Nuts are tightened down onto the studs to hold down the manifolds.  This prevents the problem you are having.

[jacksoni]

Sounds like the header bolt holes are barely .500" deep. How deep are the rest of them? Seems like machining error to me. Might run it by Dart and see what they say.

[Stainless1]

I'm with Jack on that... my preference is at least twice the bolt diameter when going into aluminum.
What torque is called out for those bolts?   

[manta22]

Stan- Yes these are the recommended bolts for this header flange and Fel-Pro gasket.

WW- There is not much room between the bolt holes in the flanges and the tubes on a SBC header. These bolts are a "reduced head" so that you can get a 3/8" hex wrench on them. I think a nut would not fit leaving wrench or socket clearance.

Jack- I think the threaded depth is about 0.925".

Bob- There is plenty of engagement, over 2 x 0.375". Dart calls for 35 ft-lbs torque on the header bolts.

Regards, Neil  Tucson, AZ
 

[Peter Jack]

Neil, how thick are your header plates. I've always used 3/8" plate as a minimum. I've never seen headers with 1/4" plate flanges that seal properly for very long.

Are the holes tapped to the bottom of the hole. You may want to invest in a bottoming tap of the correct size and thread and go through each hole. It's worth getting a proper aluminum tapping fluid such as A-9 or Alumicut when you do the tapping.

Pete

[manta22]

Pete;

These are Schoenfeld SBC headers. I think they have 3/16" thick flanges.

Regards, Neil  Tucson, AZ

[Peter Jack]

That sounds like something built for the ultimate in weight saving. Schoenfeld build a lot of oval track headers and those guys sometimes do some ridiculous things to save weight. Keep a close eye on them because they'll likely have a tendency to warp.

Bo's idea of using studs is a good one and totally legitimate. You can get reduced head nuts similar to the bolts you're using now. Using them will reduce the wear on the threads in the heads. Just be sure to adjust the torque values if the studs are fine thread.

Pete

[tauruck]

Neil, I think Bo is on the money.
Studs make fitting so much easier especially on headers.
I know you'll resolve the issue no problem.

[manta22]

Pete;

You are right, these are circle track headers. That must explain why the screws bottomed out in the holes- thinner flanges.

I wasn't aware of reduced size hex nuts; I'll check into those.

This forum is so helpful, I learn something here all the time- thanks!

Regards, Neil  Tucson, AZ

[jacksoni]

Pete;

You are right, these are circle track headers. That must explain why the screws bottomed out in the holes- thinner flanges.

I wasn't aware of reduced size hex nuts; I'll check into those.

This forum is so helpful, I learn something here all the time- thanks!

Regards, Neil  Tucson, AZ

Not so much hex nuts perhaps. 12 pt. I use them a lot on my engine. ARP has them.

[salt27]

The downside to 12 point is that you can't use an open end wrench on them.    

  Don

[jdincau]

These work well but you need to locktite the studs in place as the lock nut is pretty aggressive.

http://www.aircraftspruce.com/pages/ha/nut_hex/ms21042.php