Engine part compatibility question.

scoflaw said:
There's no info on that replacement head. You need a replacement head of the correct generation. What gen. is your engine?
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Most likely a Mark VI but could be a Mark V. Mark VI engines were introduced in 1996.
 
Usually marine is a couple of years later than automotive. Easiest thing to do would be replace the valve seats, that would put everything back to spec unless someone cut a lot off the head surface.
 
Hoplite808 said:
The engine serial number is OF764186.
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That is weird......that serial number doesn't exist in the Mercruiser serial number lookup. Is that the right number? At least for me.....having the serial number gives me all the other parts associated with the engine.

In your case, your signature shows a Gen V 7.4 MPI engine. That would definitely be in the Mercruiser look up unless the block was replaced at some point.
 
scoflaw said:
Usually marine is a couple of years later than automotive. Easiest thing to do would be replace the valve seats, that would put everything back to spec unless someone cut a lot off the head surface.
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Less than $200 to move over to an adjustable valve train. Or, a bit more to change the push rods.
Hard to believe the machinist sank the valves that much and didn't change the seats; I suspect the head was also milled significantly.
 
So to answer your original question.......are the intake ports oval or rectangle? The O'Reilly head is oval for example. In all likelihood you have ovals as well (since the higher output 7.4s had rectangle intake ports and adjustable rockers) and it will work fine for your application. Yes, the combustion chamber size could be different but for your application.....I doubt it would make a big difference.

The only thing I am troubled about is the Serial Number on the block.

Effectively you have torque down rockers which a number of lower HP Gen 5 engines had as a cost reduction method for engine assembly. As you have discovered.....any work to the valve seats causes the geometry to be thrown off. Your machinist should have known that and replaced the seats to maintain the original tolerances.

For $300 buying a replacement head and using it is not a big deal on a 1996 engine with probably over 1,000 hours on it.

Screwing around with the old head to get it right is going to cost you more than that.
 
There's a difference in the cooling holes in the diff. gens. They aren't all interchangeable. Figure out what gen you have and replace with same.
 
scoflaw said:
There's a difference in the cooling holes in the diff. gens. They aren't all interchangeable. Figure out what gen you have and replace with same.
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He has Gen 5 showing below his Avatar. Pretty easy task to get the new head and match it up ......if it isn't right it goes back.
 
Just have a good machinist install new sear and new valve in that cylinder only
 
PlayDate said:
That is weird......that serial number doesn't exist in the Mercruiser serial number lookup. Is that the right number? At least for me.....having the serial number gives me all the other parts associated with the engine.

In your case, your signature shows a Gen V 7.4 MPI engine. That would definitely be in the Mercruiser look up unless the block was replaced at some point.
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I believe he wrote it down wrong if you did the copy and paste. Replace the first digit with a zero and it comes up as a gen V.
 
Let me offer a perspective. Most of us try really hard to give the best of what we know to people asking questions. Sometimes though.....we turn a simple question into a lot of other questions because........ we can and we want the bigger picture. ;)

In this case the OP just wants his engine to run and most likely would like to avoid another machine shop. I can appreciate that as his experience thus far has not been great. Buying a rebuilt head for $300 and matching it up or sending it back doesn't seem like a big deal to me on an engine that is 26 years old and has probably over 1000 hours on it.

Yes....the OCD that goes along with looking up Serial Numbers and comparing parts is engrained in my thinking but sometimes as Freud said........"a cigar is just a cigar".:)
 
One thing to keep in mind is that the reman is only as good as the guy and his machines doing the work.

With a non-adjustable valve train how much head surface has been removed is critical. Every valve should be checked when assembling and the process is the same as if they were adjustable.

When you get to 0 lash it should take between half to a full turn on the bolt when you get to 40 lbs.
 
PlayDate said:
Let me offer a perspective. Most of us try really hard to give the best of what we know to people asking questions. Sometimes though.....we turn a simple question into a lot of other questions because........ we can and we want the bigger picture. ;)

In this case the OP just wants his engine to run and most likely would like to avoid another machine shop. I can appreciate that as his experience thus far has not been great. Buying a rebuilt head for $300 and matching it up or sending it back doesn't seem like a big deal to me on an engine that is 26 years old and has probably over 1000 hours on it.

Yes....the OCD that goes along with looking up Serial Numbers and comparing parts is engrained in my thinking but sometimes as Freud said........"a cigar is just a cigar".:)
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The problem is with anything rebuilt the dimensions are different. With a non-adjustable valve train the dimensions make a difference. That is what the OP is seeing now where the valves are being held open. I do also question the machine work and lack of dimensional information to correctly set the valve train. The OP is trying to figure out a way to fix his problem and not take the heads off nor spend a lot of $$. He has two ways, maybe three, to do this - change the push rod lengths, shim the rocker arms up, or install adjustable rocker studs. I would opt for the last as the first one is labor intensive requiring specialty tools, and the second I don't know if it even exists.
He could install the adjustable shaft studs and be done with the work in two hours for a couple hundred dollars. The only thing lacking is confidence in the machine work done on the head.

Regarding the push rods there are about four different lengths in this picture that I ordered to get the valve train set up correctly on one of my engines. It's a pain to go this route.
IMG_7261.jpg
 
Keep in mind if #7 is buried deep in the head the stock pushrod will be incorrect for proper geometry/ longevity even after preloading the lifter correctly.

Fix it right and don't bring anything back to that last guy.
 
ttmott said:
The inexpensive way out is to convert to adjustable rockers. Comp Cams makes an adapter stud kit to do just that.
Check this out for your situation; I'd call Comp to make sure -
https://www.jegs.com/i/COMP-Cams/249/4514-KIT/10002/-1?parentProductId=764287
Just make sure the rocker sweeps across the valve stem correctly on that cylinder in question.
Here is a blog on the subject -
http://garage.grumpysperformance.co...ck-chevy-gen-v-vi-to-adjustable-rockers.4564/
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Thank you for this reply. I think this kit from JEGS will be the least expensive fix for me.
 
Hoplite808 said:
The machinist I have access to can't find a source for the oversized valves, guides, and seats in this head. My preference of course would be to not pull the head, again, and spend several hundred dollars on gaskets but I think I've exhausted options for that and the only way to fix it now is a rebuilt head sourced from somewhere else. I can't afford to dump thousands more into the boat right now. Which is why I asked if the Oreilly head is the same as the Mercruiser one. It would save me a small fortune if it were.
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Your old head will have a casting / part number on it. That will be needed to match the old head to available new / rebuilt ones.

TTmott's link would work for you.
 
Find a cylinder head core bank they are around. Give them the casting numbers and the will get you the correct head
 
Take your GM casting number from the old head and give it to O'REILLYs and they should be able to get you the correct replacement. Don't tell them it is for a boat. To much information will just confuse him. You could also take the casting number to a GM dealer and ask them for the correct part# for that head and go from there. You could also buy a new bare head and transfer the valves etc to the new head. If it has a GM casting # it was made by them and can be replaced with one.
 
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