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Mercruiser 350 heads

wellcraftnova230

Contributing Member
"Hello All,
So the heads


"Hello All,
So the heads on my merc 350 need to be rebuilt due to one of the cylinder valves destroying the seat. Is there any way to repair this seat besides taking it to an engine rebuilder? I just got a quote for a complete rebuild for my heads of $325 per head! Is this ridicilous, or should I just man up and accept it? Also, I taked to someone and they said it may be due to a problem with the ignition or fuel system that would cause a sticky or burnt valve. The only possibly that I can think of would be the petronix ignition that I put in to replace my points. I am thinking about going over to a mallory conversion, could this possibly be a problem? Let me know, I am trying to keep the cost down. Thanks Jon"
 
"Ask him how the ignition syst

"Ask him how the ignition system would cause this. Ask to see the valve. If it has rust on it, it could be that the motor hasn't been fogged properly for winter. It could also be that the valve is bent. Valve seats are usually pressed into their location- it's a separate part of hardened steel. Most automotive machine shops can replace it. Call around and get alternate prices. One valve seat being destroyed doesn't equal both heads needing repair.

Where do you buy your gas- at the marina or do you haul it in? Who has been doing the maintenance on the boat- the same person who wants to do the work now?"
 
"Jon,

Cost for rebuilding


"Jon,

Cost for rebuilding heads is commensurate with what damaged. Any machine shop should be able to rebuild your heads... not necessarily a marine repair facility (they're Chevy heads). Also - look for new or reman replacements (complete with valves and springs) as that might be a cost effective alternative. Keep in mind that there are lots of permutations with different head castings, valve sizes, plug angles and spring tensions.

Your problem is not likely to be ignition. Mallory makes great ignition stuff, btw. Fogging is not the issue.

Burnt valves can be caused by excessively lean mixture conditions under load. If you just have worn out seats - that can happen over time or as a result of using unleaded fuel over a long time in an early engine meant for leaded fuel. Depending on what year your engine is, it may or may not have hardened valve seats. Everything has hard seats these days but early (pre mid 70's perhaps?) heads had soft seats designed for leaded fuel.

The common machine shop procedures are to:

*disassembly
*hot tank and clean
*magniflux to check for cracks
*grid or replace the seats
*check and surface the deck and ports
*replace a burnt valve or two
*"lap" valves
*replace valve seals
*reassemble

Recommend you repair or replace heads in pairs, btw. That way you know you won't have to take it apart again for the same thing anytime soon.

hays"
 
There's millions of heads

There's millions of heads for that motor out there. Be darned if I'd pay that much to get the heads rebuilt. Find some other ones.

Jeff
 
"Cylinder head work lots of ti

"Cylinder head work lots of times means just a switch out for a reman. Cylinder Head. Add mark-up by the mechanic Plus labor. Nothing wrong with this..SOP. Places like Americal Cylinder Head in Oakland Ca,(largest operation of this type on the West Coast) does volume meman. business direct to anyone. About $130/ GM/Ford per head PLUS CORE/SHIPPING. Specify correct head #, give 'em a call and ask them to check stock. I keep a spare set of heads/manafolds/risers in the garage. If the engine ever blows, all I'll need is a short block."
 
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