Inliners International Forums General Discussion Engines Chevy-GMC timing covers

Do 235/261 Chevy and 270/302 GMC use the same timing cover?

I'm not absolutely sure, but I think so. The front motor plates are interchangeable, and since the cover mounts the the front of that I think they are compatible. The only thing I'm not sure about is if the harmonic balancer oil seal matches.

I can look at my '62 261 and my '55 302 when I get home and see if there is any difference.

The timing cover and the front plate will interchange, however the motor mount configuration on the front plate may vary. As you probably know, the holes for the 1/4" bolts that attach the bottom of the front cover from inside the pan can be tapped to 5/16" and the holes reamed in the front cover so you can access all the fasteners from outside, makes cam changes much easier.

Titen, Thanks. I thought that was the answer but didn't have a 235 to look at. There's a bunch of Chrome 235 covers on eBay and I was wondering. Yea ,changing those bottom bolts is a must. What were they thinking? Engineers!!!

Titen,Your post addressed a specific problem I am having with my 59 235. You say the bolts thru the main bearing cap are 1/4" and the holes tapped to 5/16". The bolts in my engine are 5/16" and were threaded into the timing cover holes. I wanted to make the mod that I have read about, i.e. to drill and thread the holes in the brg cap for 3/8-16 bolts and to drill out the timing cover holes to 3/8". That way I could use 3/8 bolts or studs in the cap to attach the cover. I find, however, the holes in the bearing cap are about 11/32" which is a little to large for the 3/8 tap to give a full thread. I am wondering if that would be enough strength to serve the purpose. Anybody else run into this problem?

If that's the case think about a Heli=coil, which should work.

I have always taped the holes in the front main cap to attach the timing cover. 3/8'-16 I have found that header bolts (cap screws) work the best. They have a 7/16" wrench size for ease of attaching with a wrench or socket....Good Luck

I tap the main cap and use 5/16 Heli coil instead of just tapping it to 3/8 inch.This gives a little more "room" to slightly adjust the cover to get the crank seal centered properly.

Tony P, the holes in my cap are a little larger than the 21/64 size drill recommended for the 5/16 helicoil. So, to be on the safe side, since I haven't used helicoils before, I plan to drill 25/64" for the 3/8 helicoil. Wish I could have used the smaller but gotta take what I got. Thanks for the info.

Have you considered a 5/16-18 "Keensert"? It (Part Number 93340A415 in the McMaster-Carr catalog)calls for a 7/16-14 external thread, which calls for a 23/64" tap drill. Thus you do not need to drill as large a hole for the 3/8" helicoil and still have the 5/16" cap screw for ease of installation. I have had better luck with Keenserts staying put than with helicoils.

Here's how I did it

I used a 3/8-24 tap.

Deel, I probably pound a GMC harder than most and I have never had a timing cover bolt loosen using the 3/8-16. They have never leaked either. I was wrong on the header bolt. The head is a 3/8" socket with a shoulder. Very easy to get a wrench on. I use Permatex #2 for a sealant. I have also found using a exact 3/8" drill on those 2 lower holes also helps align it. GMC's and Chevys are the same.