4.1 hint

[ChrisCairns]

For anyone thinking of, or presently building a production 4.1 here's a tip....

When I was test fitting the heads on the locating dowels without the studs in the head they fit fine. Then I put in the studs. The heads wouldn't fit over the locating dowels. I filed on the underside of the dowels until this allowed the heads to fit over the dowels and the heads to lay flat on the block. Once there I was able to see light between the block and the head, but only at the bottom. I measured it and it was 12 thou. at the bottom and 0 at the top. And no, it wasn't the dowels holding the bottom up, it was the studs. I then took my machinist's (super accurate) straight edge and put it on the head and up the studs. The studs are in the block crooked. The holes have been drilled and tapped at a slight angle.

I spoke to my machinist about this and he said he can drill out the stud bores in the head a little to allow for the crooked studlies. And I'll replace the dowels with unfiled ones.

I've never come across this on the 109 block and don't know if it's just "my" particular 4.1 block that's this way, or all of them, so be warned to check.

 

[bison]

This sounds bad since the back of the head of the fastener wont be flat on the head as its torqued causing it to distort slightly and dig into the head. Id have it squared up in a Bridgeport and thread holes milled and have thread inserts installed to correct the thread angle.

 

[Robert Wilson]

I have 1 hole in my current 109 block (bottom rear passenger side) that I have to put the stud in after the head is down on the dowels. The head will not go on the studs unless I leave it out. All other holes are nice and square. I have not seen it with any other blocks I have messed with.

 

[CTX-SLPR]

My 4.1 has no issues with the heads going over the studs, 1 of the studs won't thread to the hilt though despite chasing the threads repeatedly with a thread chaser.

 

[ChrisCairns]

This sounds bad since the back of the head of the fastener wont be flat on the head as its torqued causing it to distort slightly and dig into the head. Id have it squared up in a Bridgeport and thread holes milled and have thread inserts installed to correct the thread angle.

I'm thinking it will straighten out the stud, or at least put a curve into it so the washer/nut sits straight. Disassembling the short block ain't in the cards.

 

[ChrisCairns]

I have 1 hole in my current 109 block (bottom rear passenger side) that I have to put the stud in after the head is down on the dowels. The head will not go on the studs unless I leave it out. All other holes are nice and square. I have not seen it with any other blocks I have messed with.

So it does happen to the 109's also. Must be Monday blocks.

 

[ChrisCairns]

My 4.1 has no issues with the heads going over the studs, 1 of the studs won't thread to the hilt though despite chasing the threads repeatedly with a thread chaser.

Did you have the first few threads machined out in the block?

 

[CTX-SLPR]

Did you have the first few threads machined out in the block?

No countersinking was done, threads are stock and take the Hot Air style head studs.

 

[ChrisCairns]

No countersinking was done, threads are stock and take the Hot Air style head studs.

What are hot air style studs?

 

[wbrophy]

What 4.1 block casting number are you using?

 

[CTX-SLPR]

The 86-87 block is different since the threads are counter sunk into the thicker deck and they are also barely different in deck height due to the different head gaskets. I think the biggest difference is the countersinking of the threads in the deck. I know they take 2 different part numbers.

Mine is a 484

 

[ChrisCairns]

The 86-87 block is different since the threads are counter sunk into the thicker deck and they are also barely different in deck height due to the different head gaskets. I think the biggest difference is the countersinking of the threads in the deck. I know they take 2 different part numbers.

Mine is a 484

I assume the above was in reply to me. I know what the block differences are, but what are hot air style studs? How are they different physically?

And to wbrophy, mine also is a 484. (Only cool people use 484's. :biggrin: )

 

[CTX-SLPR]

Since the threads don't go all the way to the surface I think it alters the thread lengths on the studs. I never tried to put in the 86-87 studs when TA sent me them by accident so I can't tell you if they will no work absolutely but I believe they end up being too long for the hot air blocks.

 

[boostingbuick]

No fit issues with my 4.1.

 

[turbofabricator]

Chris,
I have had a few GM 109 blocks with crooked head bolt bosses. One side of the engine may be good and the other deck may have all or just a few bolts angled. I have also seen this on a 4.1 StageI block, too. Most people never notice this. The first time I found this was about 15 years ago. I was torquing a set of ported heads on a friends engine, and the two long bolts would stat to back off after applying the final torque to them. He had blown the gasket on the passenger side real bad, but the drivers side was perfect. This is something I check on every build now. The fix was to elongate the holes in the cylinder head, and then use self aligning washers under the bolt head or stud nut. Self aligning washers are a two piece deal. The top one is convex, and the lower half is concave. A liberal (sorry, bad term) amount of ARP bolt lube between all parts and it will work great. They are available from here and other places. Google "self aligning washers". Welcome to Northwestern Tools

 

[Lee Thompson]

self aligning washers

VERY good info !!!!!
Thank you vey much.

 

[ChrisCairns]

Chris,
I have had a few GM 109 blocks with crooked head bolt bosses. One side of the engine may be good and the other deck may have all or just a few bolts angled. I have also seen this on a 4.1 StageI block, too. Most people never notice this. The first time I found this was about 15 years ago. I was torquing a set of ported heads on a friends engine, and the two long bolts would stat to back off after applying the final torque to them. He had blown the gasket on the passenger side real bad, but the drivers side was perfect. This is something I check on every build now. The fix was to elongate the holes in the cylinder head, and then use self aligning washers under the bolt head or stud nut. Self aligning washers are a two piece deal. The top one is convex, and the lower half is concave. A liberal (sorry, bad term) amount of ARP bolt lube between all parts and it will work great. They are available from here and other places. Google "self aligning washers". Welcome to Northwestern Tools

Thanks Ken.

I just got home from the machinist's place. Dropped off the heads and will be able to get them back early next week. In the mean time I'll order some of those washers....I didn't know such things existed.

And I'll perform an exorcism on them before installation if any "liberalism" is stuck to them. :biggrin:

 

[Powder]

Thanks for the heads up!! (no pun intended:biggrin: ) My "291" block is at the machine shop waiting for my head studs to arrive so we can bore the cylinders .035 over. This will be very helpful information if I end up with the same problem.
MLH

 

[Turbo1dr]

My previous 109 had a couple of crooked bolt holes but it tightened down fine.

 

[ChrisCairns]

My previous 109 had a couple of crooked bolt holes but it tightened down fine.

My main concern wasn't SO much the clamping force, although it was a concern, it was the moving of the head upwards. If you reread my original post it explained that I had to file the underside of the locating dowels to try to make the head sit flat on the deck, because the crooked studs were forcing the the head up. So with the 4.1 bored out to 4" we don't have much "extra" movement to play with...in fact it's about 10 thou. using a 1007 gasket.

With the 1007 "O" ringed gasket it has to be pretty well perfect. Moving the head up would leave the gasket (positioned by the studs and dowels right at the deck) in it's proper position but the head's groove would not be in the right position to accept the gasket's ring since the head is sitting up higher, forced higher by the top of the studs.

Or I may be nuts. :biggrin:

Edit: When I use the term "UP" it means towards the intake manifold.