Exhaust Manifold Bolts:

40ford

40ford

Well-known member
I replaced the exhaust manifold gaskets on pass. side of my truck about two years ago because I had a leak.I used grade 8 bolts with lock washer.I noticed today it sound like a very small leak starting?I checked the front two bolts and they were loose and will not tightened?Now what can I do?I got a longer bolt and tryed and still gets snug but will not tightened.Got a bad feeling about this?
1952 F-1 239 Flathead 8RT
 
Remember the front bolts are a different size than the others. I wanna say 7/16-14 but double check the size before installing a bolt. If your bolt is already the correct size and it will not tighten, check the threads on the bolts as well as the block.
 
The bolt holes for the manifolds are blind holes. If you put too long bolts and tighten too much you can crack the block into the water jacket. Make sure the bolts are short enough not to bottom out, If the gaskets keep blowing, you might have warped manifolds.
 
40ford said:
I replaced the exhaust manifold gaskets on pass. side of my truck about two years ago because I had a leak.I used grade 8 bolts with lock washer.I noticed today it sound like a very small leak starting?I checked the front two bolts and they were loose and will not tightened?Now what can I do?I got a longer bolt and tryed and still gets snug but will not tightened.Got a bad feeling about this?
1952 F-1 239 Flathead 8RT
Click to expand...

Besides the FRONT bolts being 7/16", you surely don't want to use a bolt that is too long, because in that area, it is easy for a bolt to break-through to a water jacket. DD
 
So do I need two 7/16 bolts for the upper and lower in the front?I hope I have not done some damage here?
 
40ford said:
So do I need two 7/16 bolts for the upper and lower in the front?I hope I have not done some damage here?
Click to expand...

Yes you do need 2 7/16 bolts for the front as advised.
I would remove a bolt then measure the depth of hole and then get the correct bolt length so as not to bottom out and cause further damage.
hopefully you may haye fitted the smaller size by mistake and all is not lost.
best of luck.
Phil NZ
 
I am not an expert but, lock washers on exhaust manifolds tend to crack and break over time due to the heat cycle. That can cause leaks. I always use just flat washers. I use socket head cap screws with lots of anti seize. Hope you solve your problem.
 
I'm with 19 fordy... But I'm still hex-head. Anti seize and flat washers. I always try to find the thick washers.
 
"Flat" is where it's at.
We all know that!

I actually have also used bronze bolts in the past.
 
Gotta say the stainless route is a great way to go as well. Some of you know I have done a lot of work with old toyota landcruisers. They have a problematic flapper/heat riser in the exhaust manifold. Mine always leaked and hissed from the pivot and I hate manifold leaks. I pulled mine out and to do so had to remove two #2 phillips screws that held the flap. I simply unscrewed them like thgey were installked them the day before. Then I put a steel bolt straight through the manifold with gaskets at each end and no flapper. It lasted less than a year. When it failed it was about as thick as a human hair in the center, then broke in half. I went up to my attic hoard and found the stainless shaft I had pulled and it was like new. I installed a stainless bolt this time and it is still in there 35 years later. Stainless does really well in the hot zone.
 
Last edited:
OK,I got the correct size bolts today and installed just snugging them.I cranked truck up and let everything heat up and tightened bolts up.I was worried about maybe cracking the manifold?It is quiet now but just wondering if I should have tried to remove gasket and replace?Thanks men for all the help.
 
A better way would use studs that are coarse on one end and fine on the bottom end. That way you can screw the studs in as far as they’ll go without hurting the block, then with fine nuts holding everything on you can tighten them a lot without worrying about hurting anything while using all the threads so the studs won’t pull out.
I just did that last week on an 8BA install on a ‘46 Mercury.
It might be hard to get the pipe flanges over the studs but this Merc has dual exhausts so that wasn’t a problem.
 
Sorry for bringing this post back up but I’m planning on going the stud route on my ‘41 24 stud and am wondering where everyone is sourcing their studs from and what length do I need?
 
Slightly off topic, but the French flatheads use studs at the exhaust faces, but they are metric M10 fine
 
You must log in or register to reply here.
Back
Top