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I just bought a set of 4 bolt main caps and they are all 964#’s except one which is a 984#. The guy said they came off the same block but the 984 says 23gm and the 964’s say 24gm. Is this a big deal and are they definitely from different engines?
I just bought a set of 4 bolt main caps and they are all 964#’s except one which is a 984#. The guy said they came off the same block but the 984 says 23gm and the 964’s say 24gm. Is this a big deal and are they definitely from different engines?
The problem is GM does not drill the same hole twice in the same spot, Changing caps from one block to another in most cases really does not work out very well.
If you bought caps to put on another block its almost insignificant as they or the block may take machining to make it all fit the way its supposed to. Before its mentioned wouldnt worry about cast vs steel caps, in most cases it just doesnt matter
As far as casting numbers, it stands to reason the rear cap came from a different mold, therefore different casting number. What are your plans for the caps?
I believe the center holes are accurately located. Shop will have to drill and thread outer holes in the block using the caps as registers. Then shave .002 or so from the caps and line bore.
I believe the center holes are accurately located. Shop will have to drill and thread outer holes in the block using the caps as registers. Then shave .002 or so from the caps and line bore.
Bogus statement cut the caps .002 again GM blocks are not that close. You may have to cut more then that or you may not have to cut anything,
In most cases the from block to block the register cuts vary quite a bit sometimes and the caps may need to be shifted to one side or the other. Some times that register cuts from block to block are off so bad it ma take more then one set of caps.
Finish should always be done with an align hone not a line bore most line boring machines can't cut the whole main line with one shot.
Line honing always brings out the imperfections of line boring, Believe me
Last edited by BROKEN RODS; Feb 17, 2018 at 04:43 PM.
Bogus statement cut the caps .002 again GM blocks are not that close. You may have to cut more then that or you may not have to cut anything,
In most cases the from block to block the register cuts vary quite a bit sometimes and the caps may need to be shifted to one side or the other. Some times that register cuts from block to block are off so bad it ma take more then one set of caps.
Finish should always be done with an align hone not a line bore most line boring machines can't cut the whole main line with one shot.
Line honing always brings out the imperfections of line boring, Believe me
mine thing I noticed is the bolt holes in the caps are so varied in size that I can’t make a mandrel for all holes I’ll have to make a mandrel for each individual hole to line up for drilling. With that being said there is enough difference in ID of bolt hole and OD is bolt shoulder that you have .050 of play anyways so it seems as long as you have the main bearings in and tighten the center bolts you should be lined up for the outer bolts? Does that sound right?
A lot of people think this is a bad idea. Do the caps fit in the recessed area where the old caps sat? Do the inner bolts screw down tight without binding? And do the bores the bearings sit in come close to lining up?
A lot of people think this is a bad idea. Do the caps fit in the recessed area where the old caps sat? Do the inner bolts screw down tight without binding? And do the bores the bearings sit in come close to lining up?
i bolted them on today and they actually felt very good and lined up with a nice transition on the ID from cap to block. I know it only takes thousandths to be bad so I can’t say for sure but they did bolt up nicely. I know there is risk and I know it makes sense in some cases to just find a 4 bolt block but people have successfully done this and the block I guess has some sentimental value or I’d just buy a dart block. I’m just trying to get feedback on the right way to do this and what to watch out for. I machine parts in my line of work for pharmaceutical equipment but never done any sort of engine work as far as machining goes.
Take 'em to your machinist with the bolts or studs you intend to use. Most machine shops save caps off of junk 4-bolt blocks. If yours aren't perfect, they may mix and match with some of theirs before they line bore or hone.
i bolted them on today and they actually felt very good and lined up with a nice transition on the ID from cap to block. I know it only takes thousandths to be bad so I can’t say for sure but they did bolt up nicely. I know there is risk and I know it makes sense in some cases to just find a 4 bolt block but people have successfully done this and the block I guess has some sentimental value or I’d just buy a dart block. I’m just trying to get feedback on the right way to do this and what to watch out for. I machine parts in my line of work for pharmaceutical equipment but never done any sort of engine work as far as machining goes.
You are lucky !!! Most of the ones I have gotten in the shop turns into a train wreck.
Here is a block that came in for 4 bolt replacement billet caps, But after looking things over the register is .050 offset from the center line of the main line. If you measure from the outside of the cap to the bolt holes it .100 difference. There is only .065 to machine out of the caps. In the end I had to put on Splayed caps to have it come out right.
You are lucky !!! Most of the ones I have gotten in the shop turns into a train wreck.
Here is a block that came in for 4 bolt replacement billet caps, But after looking things over the register is .050 offset from the center line of the main line. If you measure from the outside of the cap to the bolt holes it .100 difference. There is only .065 to machine out of the caps. In the end I had to put on Splayed caps to have it come out right.
4 bolt main caps #s
