[Tim Corcoran]

I have the longer dowel pins (7/8") and they are a bit oversize as well (.3125). I plan to get the fitted to the block and caps fitted correctly with new 4 bolt main caps on caps, 2, 3 &4. Once all fitted to my satisfaction then it goes to the machine shop for line bore & hone, the bore the cylinders with a torque plate. No one cares about your engine as much as you do so good enough for the machine shop may not be good enough for me. I was trying to get some advice on the reaming process. Thanks

[tc]

Standard dowels ( not under or oversize ) are actually two tenths ( .0002 ) larger than nominal fractional size. Reamers are sized
press fit- one half thousandths under nominal size ( .0005 )
on size- same as nominal
slip fit- one thousandths over nominal ( .001 )

I have built a lot of dies and have never used a press fit reamer on any of them. A properly on sized reamed hole will have a nice tap fit with the dowel. That .0002 is enough.

Only time I use a press fit reamer, ( that will be .0007 press fit ) is if the dowel is used as a stop or locating a part for production people to bang into on a fixture or some type of tool.

I would use the press fit reamer in the block to be sure of a tight fit.

Also, even though we are taught dowels just locate and the bolts hold the block in place, we use longer dowels in from blocks ( die ) to help hold the block in place ( especially if they double part the die ). So we have the dowel go one inch into the die set instead of 1/2 inch. Dowels holes in a die set can become elongated with too much side pressure from the form block if the dowel is not far enough in the hole.

[Tim Corcoran]

TC

Thanks for your reply, let me start over then. The dowels removed from the block mic .309 and they were very tight. The new longer dowels mic .3125 so to use them, the block and the caps would need to be reamed but finding the correct size reamers is a challenge or maybe not available. Now I'm thinking the best way forward would be to get 1 inch long .309 dowels if I can find some. What are your thoughts.

[KEN CROCIE]

The bottom of the hole on the stock cap can enlarge with age, giving inconsistent main bearing saddle measurements. This can be remedied two ways. A longer stock diameter (.309") dowel can be used so that it will protrude into the cap deeper, getting into the unworn part of the hole the original dowel never reached, or use commercially available 3/16" (.3125") dowels these must be fitted by a machine shop that can perform non-routine machine work.

[Tim Corcoran]

I located some .309 dowel pins that are 1.5 inches long, Dura-Bond AD-006-P Summit sells them for $7.99 each, I need 10 so kind of expensive for a dowel pin. I found another company (Star Performance) that sells the same Dura-Bond pins for $1.45 each. Summit is really marking up that item. Are these pins made from the right material and the correct heat treat to be used as a main cap for a race engine.

[Skip Fix]

http://www.precisionautomotivespecia...owel-Pins.html

Here are some I saw mentioned here awhile back

[tc]

If your pins are .3125 dia, then they are not dowel pins from a tooling standpoint or they are made wrong. They would have been ground too small and I have seen that here at work with a lesser quality brand dowel pins. So make sure your mic is right and you are measuring correctly, should be .3127. There should be no problem finding a reamer sized .3120, .3125, .3135 for a 5/16 dowel pin.

Anyway, if someone was to put larger diameter, longer dowels in the cap and block, the pins have to be put in parallel to each other or the cap will not go on ( or off ) easily. Not something to ream by hand.

[Tim Corcoran]

Originally Posted by tc

If your pins are .3125 dia, then they are not dowel pins from a tooling standpoint or they are made wrong. They would have been ground too small and I have seen that here at work with a lesser quality brand dowel pins. So make sure your mic is right and you are measuring correctly, should be .3127. There should be no problem finding a reamer sized .3120, .3125, .3135 for a 5/16 dowel pin.

Anyway, if someone was to put larger diameter, longer dowels in the cap and block, the pins have to be put in parallel to each other or the cap will not go on ( or off ) easily. Not something to ream by hand.

I got the .3125 dowel pins from Butler Performance, these are the same pins they use on all their engine builds. A .3125 dowel pin is 5/16 and is a standard pin size. Why do you say they are made wrong? My mic is correct I have a 1.0000 standard that I check the mic with and it's right on. Any how I ordered some long .309 dowel pins today and if everything fits up properly I will use them that way I don't have to ream the block and the caps. Thanks for your response.

[tc]

https://www.holo-krome.com/uploads/7...k.usa.dp.p.pdf

I talked about dowel sizes to show why you could not find a .001 undersize reamer. That would be .0012 press fit and that is too much.

Your pin is probably made to be .3125, but dowel pins used in tool making are .0002 over and thus reamers are sized according to that.

[Dragncar]

The factory pins are pretty soft. On my 4 bolt 455 HO block I noticed the dowels were kinda pushed down on a refresh.. Not all that much showing with a big bevel.
I drilled tiny holes is a few of them and threaded them and pulled them back up with a slide hammer.
It worked well enough to get 10 more seasons out of the block.
I was surprised how soft they were. I thought a drill would not touch them.
When I put the block back in service its going to get a proper dowel fitting and line hone.

[tc]

If you read at the bottom of the page in the holo krome link, you'll see how hard dowel pins are we use. A drill bit will not drill thru the case hardening.

[Tim Corcoran]

I used a dowel pin extractor to remove the main cap dowels in my block. They were very tight, I was able to get all but one out, I tried to drill it out and no drill would even mark a mark on it, very hard heat treated steel. I got the oxy acetylene torch out and got the pin cherry hot put some penetrating fluid on it and then was able to pull it out with the extractor. For our discussion the dowel pin's primary purpose is to locate the cap and the bolts/studs apply the clamping force to oppose the extreme forces, but the pins also help stabilize the cap and a good tight fit of the pins is key. When there is not enough engagement of the pin into the cap the hole in the cap can become elongated and this demonstrates that the pin does more than locate. Putting in a longer pin further into the cap does provide more stability.

There are various grades of dowel pins used for a variety of uses. I needed to put longer dowel pins in the back of the block for aligning the trans because with the mid plate there just wasn't enough engagement into the trans. I had to remove the existing pins and I tried every trick in the book and could not remove them, so I drilled them out. These pins are much softer than the pins that locate the main caps as a HSS drill bit did the job.

[Tim Corcoran]

Originally Posted by Skip Fix

http://www.precisionautomotivespecia...owel-Pins.html

Here are some I saw mentioned here awhile back

Skip, thanks for sharing the link I also found those same pins and look like a great product. By the time I found these I had already found another source of some .309 pins but they are 1-1/2" long and I will need to cut them to size.

[Tim Corcoran]

Originally Posted by tc

https://www.holo-krome.com/uploads/7...k.usa.dp.p.pdf

I talked about dowel sizes to show why you could not find a .001 undersize reamer. That would be .0012 press fit and that is too much.

Your pin is probably made to be .3125, but dowel pins used in tool making are .0002 over and thus reamers are sized according to that.

TC, thanks for the info

[Skip Fix]

Maybe similar on factory 4 bolt caps but I noticed on the Programs there is a depth to the hole vs 2 bolt caps that have a "through" hole. The material between the 4 bolts is why no through hole on them. So also something to consider on longer ones on the 4 bolt caps.

[tc]

Originally Posted by Tim Corcoran

TC, thanks for the info

You're welcome. Too bad you don't live closer and I have my mill ready to use, it would be fun to put larger dowels holes in the caps and the block.

[Tim Corcoran]

Originally Posted by tc

You're welcome. Too bad you don't live closer and I have my mill ready to use, it would be fun to put larger dowels holes in the caps and the block.

That would be cool

[RUDOLFSSON]

I upgrade to harder 8mm dowels .... it's a great next size up

The metric machinist :-)

[Tim Corcoran]

If I use a larger dowel, I will need to ream the block and the caps, I decided not to take on that task. I decided to use these pins that are the correct O.D. but 1 inch long. http://www.precisionautomotivespecia...owel-Pins.html

The factory pins are plenty hard.

[74Grandville]

I ran into this with my 428 build. the original dowels were pressed deep into the block. I think someone put the block on the floor without the caps. With help from a friend, we welded a stud to the end of dowel and pulled them all out. I wanted to avoid line honing or messing with larger dowel pins. I ended up buying .310 pin bore gauges and cut them in half. they were about 3/4" long after cutting them and drove them into the block. I measured the main bores after installation, and they all checked out. It worked great for me, and the engine is running fine.

I attached a pic of the new dowels in the block