Anyone ever disassemble a cylinder head? - SailNet Community
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post #1 of 13 Old 07-09-2010 Thread Starter
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Question Anyone ever disassemble a cylinder head?

Hi, I am new here... have a 34' catalina with a Universal M-25XP. To save money, a friend has offered to change the head gasket for me, but for the life of me, I can not find anything online that tells you how to disassemble the cylinder head... plenty of places to show how to assemble... but not disassemble.

Can anyone direct me to a link or have a tip on this... my friend swears that disassemble is different from assemble.... I had asked him why he could not just go backwards from the assemble directions.
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post #2 of 13 Old 07-09-2010
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He's right, you turn the bolts/nuts in the opposite direction.

Sorry that was my attempt at humor. Can you just order a manual? It might be handy to have for future issues. Although disassembly is usually easier, I do agree if you don't have the experience it would be a good idea to have the manual.
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post #3 of 13 Old 07-09-2010
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First off lets get some basic terminology sorted out.

Disassembly of a head means specifically to tear the head COMPLEATLY down..i.e. Remove all the valve springs and valves in preparation of doing a head job.

Removal of the head ( what your needing to do ) for a head gasket replacement only, is not a disassembly.

Revert to previous post about turning bolts to the left...that's all you really need to know...Torque sequence is only important for assembly on that particular engine not disassembly.

Good luck..and Have fun...learning about your engine can/will give you more piece of mind then any other component of your boat.

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Last edited by Stillraining; 07-09-2010 at 10:16 AM.
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post #4 of 13 Old 07-09-2010
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The pictures tell the tale:

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Remove alternator, alternator belt, valve cover, disconnect exhaust manifold from flex line to water lift muffler, disconnect (and cap) fuel lines, remove rocker assembly, remove pushrods, unbolt head, remove head. If all you are doing is replacing the head gasket, you shouldn't have to remove the exhaust manifold from the head.

Have you got a torque/tightening pattern for the head studs, so you know which nuts to tighten at which time and how much, when you put the head back on again?

Don't forget to check decompression lever adjustment when you put the valve cover back on. Details here:

Universal M-25 Images and Specifications - Universal Diesel Engine Owners Manual - Marine Diesel Direct / Torresen Sailing Site
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post #5 of 13 Old 07-09-2010 Thread Starter
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Thank you

Thank you kindly and also thank you for the humor...
bljones - my friend finds the link with pics very helpful... I am fairly new to the boat as well... and awaiting past owner to send me the manuel...
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post #6 of 13 Old 07-09-2010
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Yeah, if you're just replacing a head gasket, no reason to tear down a cylinder head. If you need to take the head apart, PM me for more details.

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post #7 of 13 Old 07-09-2010
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One more thing- before you reinstall the head, check to see how "true" the surface of the head is. You're gonna need a set of feeler gauges and a metal straight edge for this. Lay the metal straight edge (on edge) across the surface of the head diagonally from corner to corner. You shouldn't be able to slide a feeler thicker than .002/ .004" (sample numbers only- I am not sure what the exact spec for Universal is, but it should be somewhere on the web) under any part of the straight edge, except for the valve seats. Don't have a feeler gauge? the quick and dirty method is to use a strip of notebook paper.
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post #8 of 13 Old 07-10-2010
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So far so good with the advice. In all fairness to those who have posted, it is important to know and correctly apply the torque specifications. Got 35 years around thumpers and floaty things in general, including (but not limited to) 17 years in a shipyard, second engineer in a 158' dragger, ad nausium.

The pattern is not that important, starting at the centre of the head and working towards the ends is ! The gasket will stretch as torqued and a centre start allows the material to "flow". Don't apply any other sealing material to the head gasket and check that the securing bolts are either sealed or lubricated, depending on manufacturer and wether the bolt holes are "blind" or carry through into the water jacket. Do not remove the injectors from the head but be extremely careful that you don't damage the injector tips due to careless hadiling. ensure any and all open fuel system parts are either plugged or otherwise protected from any ingress of dirt. It ain't rocket science, take your time and it could be a large learning experience, the most important thing to remember is three words, CLEAN, CLEAN, CLEAN.

Hope this is some assistance,
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post #9 of 13 Old 07-10-2010
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And then of course you'll have to get the low-down on re-adjusting the valve clearances which is also not rocket science but is a tad more difficult than "turning the bolts the other way."


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post #10 of 13 Old 07-10-2010
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sorry but your friend may not be the guy for this job.

and now that both you and your friend ar on the same level, I sugest that you take control, do your homework and perform the task on your own.

when 2 pepoles start desasembling an engin things get lost and confusion set's inn. sins its your engin better you do it, take your time make nots or better yet use photos as reference.
always use the proper tools, inexperience often leads to broken studs or engin bolts, if you feel something will let go, stop ask guidence on this forum.

cheers
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