[Bill Hanlon]

Forgive me for improper nomenclature here, but I have an Internet friend who needs to know the proper diameter of the bore through the main bearing caps and block for a '55 287 (actually '55 288 GMC V8). He is having his rebuilt and the main bearing inserts do not seem to settle into place firmly.

And for my continuing education ….

When a block and caps are "line bored" how does one make up for the material that was cut out? I've never heard of bearing inserts that are larger outside diameter than stock.

[tom s]

Bill,when the line bore they try not to take anything off the block side,just the caps.Tom

[Bill Hanlon]

So if material did have to come off of the block side to clean things up the block is junk?

[Jack Gifford]

A typical align-bore starts with milling about .005" off the main caps' surfaces, so the new bore is centered slightly higher in the block. Timing chains are available in slight under-lengths if the crank center is moved up significantly. As Tom said, the machinist tries to do most of the cut from the caps.

Bill- it sounds like your friend is the guy who PM'd me for that 288 info. He didn't acknowledge receiving my reply (?). As I said to him, I'm guessing that bearing inserts are the same thickness among 288, 316, 347, 370, and 389 engines. If that's true, the numbers I gave him for his 288 main bores is correct (I need to look back at the PM for them).

edit: 2.4380"-2.4390"
Is his sceen name mjvaughans?

[Bill Hanlon]

Thanks for the info about align boring the block. Makes sense now.

What is the 2.4380"-2.4390" dimension? If I remember correctly the 287/288 and 316/317 crank journals are around 2.5", so "O.D." of the bearing inserts would be around 2.5" + twice the thickness of the shell.

Yes, Mike Vaughans is the guy looking for the information.

[Jack Gifford]

I think you are right Bill. I had taken the 2.2498" mains journal diameter from a Chilton's manual, since I don't have a '55 Pontiac manual. But now I realize that I've always thought that '55 mains were nominal 2 1/2". The old H-O Racing "Pontiac V8 history" shows 2 1/2" mains also. So I'll PM mjvaughans that bores should be 2.6880"-2.6890".
Sorry for my brain-fade.

[MJVAUGHANS]

Ok guys, Mike here.

We did get the info we were looking for on the journal bores.
Jack-Yes, you were correct with your last numbers.
Bill-I learned something I did not know either about the align boring.

Further FYI, apparently there is an organization called AERA. (American engine rebuilders association I think.) This is regarded by its members as the final authority when it comes to engines rebuilding specs. They have like 4 spiral bound catalogs showing different critical spec's. Each book cost like $100. Sure enough when the machine shop got their hands on these the 1955 and 1956 pontiac V8 engines were listed and their spec's. I did not want to push my luck with the rebuilder by taking pics with my phone.(Yet at least)

We are taking things one step at a time, and it feels like we are climbing the stairway to heaven! Thanks again to both of you for your help.

[Bill Hanlon]

Originally Posted by Jack Gifford

Timing chains are available in slight under-lengths if the crank center is moved up significantly.

Time for more learning on my part, Jack.

It would seem to me that in order to make a "slight under-length" chain one would either have to take a link out of the chain (probably not "slight) or reduce the size of each link very slightly. If you reduced the size of each link you'd also have to reduce the pitch of the chain sprockets, while still maintaining the 1:2 ratio of number of teeth.

Of course this would be easy to solve with a chain tensioner, but there is not room for one inside the timing cover.

It hurts my head to think about this so hard. I'm going to bed.

[mgarblik]

At least in the case of Cloyes Timing sets, they come up with "short sets" one of two ways. First of all, EVERY performance timing set is checked on a setting fixture for center to center distance. In the normal production of double roller timing sets, because of all the stacked-up tolerance possibilities between each link, axle, and roller, as well as the sprockets, some measure short by just luck. Cloyes tell us the -.005" sets can occur just from parts selection and measurement. For tighter sets, -.010-.015" sets, they alter the pitch of the cam sprocket, we are talking about adding .0001-.0002" per tooth to tighten the set for excessive line honing operations. We have line honed our race block 6 times now and I do it very carefully. I am using a -.005 " Cloyes set and it is tight.

[Jack Gifford]

Thanks for the insight Mike.