Re: 502 low compression
 

Well, I don't know what the guy doing your heads is talking about. You can't say valves are for 454 or 502. If they are Merc rectangular port heads from Merc black engines it makes no difference if they are from a 454 or 502. The heads and valves are the same. The intakes should be 2.19 and exhaust are 1.88. some Blue engines use 2.25 intakes.

Head bolt torque depends on the gaskets, bolts and lubricant used on the bolts. The head bolts also need to be torqued in a SPECIFIC ORDER!!!!!!! You probably also need to use a sealer on the head bolts as many go into water jackets. I would get new ARP bolts and there sealer and follow their torque recommendations. I don't remember the specifics on the torque#'s but ARP's are lower because of the lubricant sealer used.

Re: 502 low compression
 

Looks like duke posted as I was typing.

Re: 502 low compression
 

Here is the bolt torque sequence to get proper sealing.

Re: 502 low compression
 

I'm with you. That raised my eyes/ears.

I'm hoping that was a case of what was 'thought what he (mechanic) said" vs this "is exactly what he said."

BTW: 502's have blind bolt holes, meaning they do not run into water. Bolt sealer not needed nor recommended. Use proper lube or oil (depending on bolts used) while also making sure that the bolts and bolt holes are as clean as possible.

BTW #2 - you may want to check the cyl head surface and block surface for straightness while you can. No reason for putting thi stuff back together if they won't seal well.

Re: 502 low compression
 

I'd make sure they check the valve guides carefully, valve seating problems are sometimes caused by badly worn guides.