Exhaust bolt threads stripped

[bmwillia]

On both sides of my flathead, the forward two bolt holes are stripped out.

What is the best option to fix this?

Heli-Coil?

Thanks!

Brad

[George/Maine]

Some times the front holes are larger and they used smaller taped holes may have threads in farther.

[Terry,OH]

The front two are a larger size than the rest, but if they are stripped you want to remove the least possible so the Heli-Coil sounds correct. DO NOT drill the holes any deeper than they already are or just enough to get the repair in place.

[51 MERC-CT]

Use caution, the front holes are 7/16" dia. threads as opposed to the rear 4 that are 3/8".

[bmwillia]

Maybe that is the problem then.

I am using 3/8" all the way around.

[Mike51Merc]

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Now here's a trivia question for the masters (which I'm not).
Why are the front holes bigger?

[Tim Ayers]

I always thought because the front crossover pipe and the front or start of the exhaust was routed in front of the motor and out of these exhaust ports. The extra weight was the reason for the larger bolts.

I'd be curious if this isn't the reason, then what is.

[JM 35 Sedan]

Originally Posted by bmwillia

Maybe that is the problem then.

I am using 3/8" all the way around.

That's a common mistake that many make, especially when not doing a stock exhaust with a crossover pipe. Your front port 7/16" threads may actually be okay.

[bmwillia]

I think you are right John.

The threads may be ok and I am using the wrong bolt. I'll pick up some 7/16" bolts today and give them a shot.

[JM 35 Sedan]

Originally Posted by Tim Ayers

I always thought because the front crossover pipe and the front or start of the exhaust was routed in front of the motor and out of these exhaust ports. The extra weight was the reason for the larger bolts.

I'd be curious if this isn't the reason, then what is.

Tim, I am thinking the extra weight/load of a stock exhaust system hanging on those bolts is part of the reason. I also feel it's the additional torque load that's required on those front bolts to pull and hold the assembly tightly together, including the sealing of two gaskets on each side, to prevent exhaust leaks. 3/8" bolts in that location would have twisted off much easier while applying the required torque, and probably even more so during removal of those bolts once the threads locked together from cycles of heating, cooling, and rusting. I think this would be similar to removing stubborn head studs/bolts. JMO

[JSeery]

Never thought about it, but wonder if anyone has actually "repaired" these front bolt holes back to the 3/8 bolt size! LOL

[flatrod]

I had a customer once that wanted all holes to be the same, so yes, I have repaired them back to 3/8-16

[JSeery]

Originally Posted by flatrod

I had a customer once that wanted all holes to be the same, so yes, I have repaired them back to 3/8-16

That is funny, any idea why someone would pay for that?

[bmwillia]

Thanks all for the input!

The problem was the wrong size bolts. 7/16 did the trick.

[George/Maine]

I noticed the same thing, I was working on a 8rt truck engine and in 53 they didn't have crossover pipe up front had a y pipe.