Bullwinkle

Anybody know the diameter of the 1968 Olds 455 bellhousing dowel pins? I believe the .625 pins I ordered are too big. I’ve seen some listings at .621. The original ones I removed seem to be .620, but I gouged them up pretty good trying to get them out before I used a homemade puller. Thank you!

nicks1966

Parts catalog list them as 21/32 x 1 1/4 part number 3712745
measured the brand new ones I have .620 x 1.20

Bullwinkle

Yeah that’s what I’m running into. The decimal for 21/32 is .65625. The .65 ones I ordered would literally have to be beat into the block with a hammer after cleaning out the port. Not sure what’s going on. Thank you for the info.

v8al

I measured a set on a 350 block and came in around .625

Bullwinkle

Thank you for the measurement v8al The .625 I bought had to be beat into the block with a brass hammer. Those .625 pins were Lakewood non-adjustable GM .007 offset dowel pins. I was able to seat them all the way into the block, but the kicker was the Lakewood backing plate AND Lakewood Bellhousing holes wouldn’t fit over the pins. Go figure… Now I am afraid when I get the .620 or .621 pins they’re gonna be too dang small.

v8al

For a 1970 Olds V8 it's part number 3736406 which I believe is a 5/8" dowel pin.

BillK

That is pretty normal on most GM blocks. I have had some that I simply could not get the dowel pins to move without using the fire wrench. They are VERY tight. I can measure a few blocks Monday morning .

joe_padavano

The 1970 Engine Assembly Manual shows 3736406, but does not give dimensions.





The Jan 1972 parts book, the Sept 1968 parts book, and the Nov 1979 parts book all show 3712745 and 21/32" diameter.





The June 1991 parts book shows 12338119 at 5/8" diameter. 0.030" is a significant difference.

Bullwinkle

Thank you Bill and Joe. I just re-measured my 1968 455 block dowel pin holes with a set of Mitutoyo calipers. I’ve always trusted these calipers, but maybe it’s time to throw them away. I’m getting .620? I checked the dowel pin holes on the NEW Lakewood bell housing and backing plate and those seem to be measuring .620 as well. I am experiencing a similar feeling as to when I get lost using a navigation system.

RWK

I would say the pins are press fit into the block, and slip fit into the bell housing, for ease of assembly, .620 would be a easy slip fit though, can't believe they would be that far undersize from nominal (5/8)
PM if you need some pins made.

Koda

I am a professional transmission to engine marriage official, or I at least provide the tools to do so, and the dowel pins are press fit into the block so they remain square and are a very small clearance fit to the transmission.

Bullwinkle

Thank you RWK and Koda. I purchased some adjustable offset dowel pins from SST to take care of the bellhousing registration requirements from Tremec for the TKX transmission. Expensive buggers.

One of the technicians at SST told me the pins measure .620, and tighten into the block, so hopefully this won’t be an issue. I appreciate all the input from everybody.

Bullwinkle

Well the saga continues. The .620 adjustable dowel pins I received from SST spun around in the block with a fair amount of resistance, but were definitely not solid / secure, when the set screws were turned all the way in.

I returned the adjustable dowel pins and the Lakewood bell housing, because the holes for the dowel pins on the bell housing were 0.010 inch larger than the .620 dowel pins (which didn’t fit in on my block).

Now, I’m back at Ground Zero and need to find the correct size dowel pins to have some benchmark to dial indicate my QuickTime bell housing which is on the way. It seems like nobody can come to agreement on what the size of the opening should be for an Oldsmobile block to aftermarket bell housing matchup?

What is the proper installation process for dowel pins? Can I do things like heat the block and freeze the pins, then tap them into the block? Do I need to take them to a machine shop and have them them professionally pressed in?

Major PITA because as soon as I get the bell housing dial indicated, I’ll have to construct some kind of puller to have them pulled right back out, so I can put the adjustable or offset dowel pins in place of them. Ugh…

Run to Rund

My various dowels, original and aftermarket offset, run .621 to .623" diameter. I routinely drill and tap them 5/16 x18 thread and pull them with a slide hammer from Harbor Freight. I generally need offset dowels to center a stick bellhousing. If tight in the block, I use a film of high pressure grease so I can remove them later. If not tight, you could use blue loctite particularly if they won't be removed later.

BillK

I think you are completely overthinking it. I have probably done this 10 times over the years and every set of offset dowels I have ever used were NOT a real tight fit in the block. They have to be able to move to adjust the bellhousing. Once you have it dialed in where you want it just mark the dowels with a magic marker or a punch so you can make sure they dont move when you put the bellhousing back on for the final time. If you want I suppose it wont hurt to put some Loctite Green Sleeve locker on them but I have never done it. Once you get it all back together and the bellhousing bolts tight it isnt going anywhere.

If it makes you feel any better, once you get it where you want it just drill a 1/4" hole through the bellhousing flange into the block mounting are near the dowel pin and put a 1/4" pin in it.