Q? about re manufactured cylinder heads.

[captlloyd]

Originally Posted by hellosailor

"R&R of a cylinder head isn’t all that tough"
No, but if you really want to do it right, you'll have to walk him through CC'ing the cylinders, and porting and polishing the valve seats too.
All easy enough "while I've got it open" but so rarely done outside of gasoline racing circles.

Whoa, just don’t see the need for that on a stock marine engine.

[captlloyd]

Originally Posted by er9

That was my original intent to do the rebuild myself but this dismantling is being done to try and solve a bigger problem. I decided against trying to do the head rebuild myself because if i screwed something up, even minor, i am worried it may continue to mask, or make worse the original problem i'm trying to solve.

Actually injector service/ rebuild is next on the list. If replacing/rebuilding the injectors solves my problem i may consider trying to do the head myself. i think i would enjoy the experience. U

HA! heat exchanger/lack of raw water flow is what started this adventure. Heat exchanged is definately scheduled to come off, inspected, possibly boiled out and zinc replaced. I have a feeling its clogged but access is really tough. i need to cut an access panel through the wall in my quarter berth first. The access panel now only about 8" height and i can only get one arm behind the engine.

im assuming you mean check/re-adjust valves on rebuilt head after a period of time? if so how long? 25 or so hours in?

If you suspect the engine overheated you might consider having the head magnafluxed to check for cracks, does not cost much.

[a64pilot]

Originally Posted by captlloyd

If you suspect the engine overheated you might consider having the head magnafluxed to check for cracks, does not cost much.

I’d magna flux no matter what, a good shop will as part of the overhaul anyway, but ask to make sure, all it is is a big electric horseshoe magnet and iron filings, but it does find cracks you can’t see.
I have seen cracked exhaust valve seats too, on a motor that had never overheated. Don’t know how or why though.

[er9]

Originally Posted by Compass790

Just a quick note to add my recent experience with refitting head. I found after 15 hrs intake v/v had virtually no clearance & exhaust v/v was way under spec so do retorque & check v/v lash. What bought it to my attention was engine losing power when hot. Had forgotten about the redo. Off today to retorque head as I forgot my torque wrench last time Too many Xmas spirits

yes too much spirits of any kind will do that to a man. thats why we consume 'after' we get back :P

[er9]

Originally Posted by puffcard

I was wondering is this gas or diesel engine. If diesel look at replacing the head bolts.

Diesel...what happens to the head bolts? weaken from stress over time?

[er9]

Originally Posted by captlloyd

If you suspect the engine overheated you might consider having the head magnafluxed to check for cracks, does not cost much.

thank you will do. i do suspect it has.

[captlloyd]

Originally Posted by a64pilot

I’d magna flux no matter what, a good shop will as part of the overhaul anyway, but ask to make sure, all it is is a big electric horseshoe magnet and iron filings, but it does find cracks you can’t see.
I have seen cracked exhaust valve seats too, on a motor that had never overheated. Don’t know how or why though.

Couldn’t agree more, always cheap insurance.

[puffcard]

Originally Posted by er9

Diesel...what happens to the head bolts? weaken from stress over time?

They weaken and stretch big time. I'm certain I blew two head gaskets because of this. The way you can check, is during re-torque. After replacement of the head during the re-torque. Back the nut off an 1/8th of a turn and see how much it takes to get back to torque. I had one took 3/4 of a turn, I thought it was going to break.

Finding the parts is getting harder for older diesels.

[a64pilot]

Some engines require head bolts to be replaced, many or most, especially the older designs do not.
Bolts hold things tight because they stretch, in fact steel has higher elasticity than rubber, it’s one reason why Springs are made from steel.
Many bolts are torqued by the wrench arc method which does not measure tightness, but rather bolt stretch.
Very high strength bolts can only be stretched a few times, from my racing days I want to think three times was it for SPS rod bolts, but old Diesel designs don’t make big HP per cu in and don’t use high speed fancy bolts, usually.
In short if your manufacturer doesn’t recommend bolt replacement, I wouldn’t, but do if they do.

[er9]

Originally Posted by a64pilot

Some engines require head bolts to be replaced, many or most, especially the older designs do not.
Bolts hold things tight because they stretch, in fact steel has higher elasticity than rubber, it’s one reason why Springs are made from steel.
Many bolts are torqued by the wrench arc method which does not measure tightness, but rather bolt stretch.
Very high strength bolts can only be stretched a few times, from my racing days I want to think three times was it for SPS rod bolts, but old Diesel designs don’t make big HP per cu in and don’t use high speed fancy bolts, usually.
In short if your manufacturer doesn’t recommend bolt replacement, I wouldn’t, but do if they do.

thanks will have to do some research and try and find out.