[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]

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.