Repro 621 bellhousing 6 bolts? 7 bolts?

[Larry B. Seaney]

I reecently purchased a reproduction of a 621 bellhousing from Keisler. It had provisions for six bolts for use in attaching it to the eng. block. It had some cosmetic issues so Keisler sent me a replacement. The replacement has provisions for seven bolts. The difference being the new housing has a bolt hole in top center of the housing behind the distributor (sbc).

I looked at some extra bellhousings I have and all of them have six bolt holes. But, my engine block has the seven bolt hole pattern. Can anyone shed some light on why the block is tapped to accept seven bolts but some bellhousings have six holes and some seven?

Thanks,
Larry

[Chuck S.]

Re: Repro 621 bellhousing 6 bolts? 7 bolts?

My original GM 3899621 clutch housing has no drilled hole on the vertical centerline.

It appears that the automatic transmissions used the seventh hole in the engine block for mounting. Since GM didn't know which engine blocks would be used in manual transmissions, and it made no economic sense to discriminate, all blocks got the drilled hole on the top center.

[Joe L.]

Re: Repro 621 bellhousing 6 bolts? 7 bolts?

Larry-----

Original GM #3899621 bellhousings had only SIX bolt holes; there was no top center hole. Kiesler makes 2 versions of the '621'. The original configuration version has 6 holes. Another version, which was never made by GM, has the 7 holes, with the top center hole added. I believe that this version is designed to work with Gen III and Gen IV small blocks (i.e. LS-series small blocks) to allow retrofit of these engines in earlier chasses. Although it's not as originally configured, I think that the 7 hole version will also work for earlier applications like yours.

[Larry B. Seaney]

Thank You *NM*