cus

Just had some 3a Heads reconditioned, they are going on a 1973 block,
the head bolt size for the 3a heads is 1/2 inch, the bolts for the '73 block
are 7/16, he said there is no need to sleeve the head bolt holes , they will
locate on the dowells, I'm a bit suspect on this, any advice appreciated,

regards, cus

gs72

He is right. The dowel pins locate the head. The bolts just clamp it to the deck.

olds 307 and 403

I have done the same thing with 5A heads on a 76 350. For one, the 1/2" to 7/16" head bolt bushings are to small for factory head bolt holes. I know because I tried them. I ended not using them, first set of head gaskets lasted 5+ years, one blew. Replaced the gaskets and drove till it burned You will have to go a hair over 1/2" for the bushings, my #6 heads that were put on a 403, the bushings fit fine and I used them. I hope those 3A heads were checked for cracks.

cus

Thanks for the replies,
Yes, they were crack tested

brownbomber77

17/32 is the drill bit. I usePro Comp bushings and they worked fine with the holes I had drilled on a set of #7 heads that ended up going back on an early engine.

cus

Also, a bit confused on bolt torque, have torqued to 85ft lbs, but just read that later heads should be 130 lbs , that's. Big difference, seems excessive with 7/16 bolts.

olds 307 and 403

Later motors used 1/2" bolts so 130 ft/lbs is the spec. Only torque them to 85 ft/lbs.

cus

Thanks, thought was the case.
Maybe that's why there were so many crack issues on later type heads, 130lbs is really
clamping them down!! not much room for expansion etc.

edzolz

I would use hardened washers under the bolt heads to distribute the load better.

olds 307 and 403

Hardened is the key word. I tried that with my 5A heads on a 76 block with regular washers, broke a head bolt. Just ran without but hardened should help.

cus

That's a good idea, but too late for know...all bolted down!
Just noticed 3A heads don't have as many bolts in the rocker box covers,
my covers will still fit but will have some boltless holes, not sure why they did that,
did the 3A's have a thicker gauge cover or something, not requiring so many bolts?

olds 307 and 403

The later engines they saved weight and cost. Ten bolts per engine when thousands are being made adds up. Just use RTV in the holes, just a dab.