The Stovebolt Site Forums The Shop Area Engine Shop 1955 235 oil pan corner bolts

Hi all, I have a stripped out driver side rear oil pan corner bolt on my 55 Chevy pickup with a 235. I've got a seepy oil pan so I decided to retorque all of the oil pan fasteners to spec...this is how I found it. Luckily it wasn't stripped to where it wouldn't back out.

I got it out but most of the threads on the bolt are gone.

I'm hoping the block isn't to buggerd up and I can run an tap in there to clean it out...maybe get away with an easy repair.

I've been searching for the bolt size/thread so I can use the correct tap but I can not seem to find it. I know the corner pan bolts are a little bigger then the flange bolts. I believe the flange bolts are 1/4-20.

I really don't want to mess with the other corner bolts...they all torqued to spec, I'd like to leave them alone now.

It looks like the corners might be a 5/16-18 bolt. Can anybody confirm or correct me on that. I can't really tell for sure because like I said the threads on the bolt that came out are pretty much gone.

Thanks guys....

Hy jaydee5150, yes the oil pan corner bolts are 5/16" n.c. (5/16"x18) hope that helps.

Thank you 3B, much appreciated. I'm pretty sure I have a 5/16-18 tap in the garage and will try and clean it up tomorrow.

I just need a little luck with that hole in the block...man I hope running a tap in there will clean it up enough to run a new bolt in there and hold to torque spec.

I'll report back on whether or not it was a success. I hope it works...or helicoil is probably going to be my fix.

A 5/16 bolt has a head size of 1/2" socket.

A neat trick: doesn't work for all bolts but quite a few or gets you very close.

1/4 bolt : numerator x3, denominator x2= (3/8) but 7/16" is what you need.
5/16 bolt : numerator x 3, denominator x2=. 15/32- (close to )1/2 " socket
3/8 bolt : numerator x3, denominator x 2= 9/16" socket
1/2" bolt: numerator x3, denominator x2= 3/4" socket
3/4" bolt : numerator x3, denominator x2= 1 1/8" socket.

Pretty nifty but doesn't doesn't work for all.

Thats right on the money...the flange bolts on the pan were a 7/16" socket and the corner bolts were 1/2".

I like that...thank you.

If the threads in the block are damaged, you may want to put a stud in that hole.
A stud will likely catch threads deeper in the hole.

Dave, that's a great idea. I'll have a better look at the thread in a couple of days. I probably won't get back to work on the truck until Tuesday.

If it doesn't clean up...I really like the stud idea. Max torque on those corner nuts is 15ftlbs...even if the threads are really bad a little red loctite on a stud might hold.

I'm still hoping it will clean up and a new bolt will do...but the stud idea is next if that doesn't work.

Get someone to drill and tap the corner bolt hole for a HeliCoil. It's a spring steel thread insert that's turned into an oversized hole and you end up with a stronger thread than original. It might even be possible to do it with the pan in place with the right tooling.
Jerry

You got it Hotrod, that's where I'm heading if the easy stuff doesn't work out.

If all else fails, HeliCoil! Be nice to keep the pan on if I have to go with a thread insert, will help keep any cast iron chips and dust out of the motor when it's drilled and tapped.

I'm really hoping the threads aren't totally gone in that hole. The bolt I took out was threadless...looks like somebody but it on a lathe and cut it smooth. I'm surprised that happened, you would think the case block is weaker then steel bolts...but it looks like the block won. Or maybe the both lost and the block threads are smooth too...we will see.

I had some time to inspect that hole. I cleaned it out really good and tried to get a good look at the threads but I had a hard tome getting a clear view. I went ahead and tried to run a thread cleaner up the hole and only made it a few turns in. When I pulled it out I had a look and saw metal...been here before! I grabbed one of my odd shaped pics and started following the threads up and was able to peel the steel threads out of the cast iron threads.

I cleaned the hole out as best I could then ran the thread cleaner up and it screwed all the way in like it should. I pulled it out and get my eyeballs up close with a flash light and the threads in the block actually look pretty decent. I did not run a tap up the hole as I didn't want to damage anything with a cross thread issue given the location and angle I had to work in.

The buggered up bolt I pulled out of the block appears to be original to the motor and was 5/16-16 1/2" long. I grabbed a 5/16-18 3/4 inch flange bolt I had in stock and ran it up. There is enough room and threads in the block to get a 3/4 long bolt in and comfortably seated.

I think I'll go with a 3/4" standard bolt and lock washer because it will grab more threads unless there is a good reason to use 1/2" only?

Also, is there any issue with using zinc coated bolts for this application?

I have had a hard time finding plain steel fasteners anymore locally. Zinc and Stainless is pretty much all they have at my local shop. There is some parkerized stuff but that's mostly grade 8 flange bolts.

Stainless into cast iron shouldn't present a problem, particularly if it's lubed with something like Never-Seez. I like the star-shaped lockwashers, as I think they have more biting edges that a regular split lock. That flanged bolt with a star lockwasher under the head would probably hold about 3 days past forever! Yes, use the 3/4" long bolt - - - -the more thread engagement the better!
Jerry