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Go Back   SailNet Community > On Board > Gear & Maintenance
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Old 11-26-2010
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Cylinder Head Bolts

I have a Yanmar 2GM20F, I had it rebuilt a few years ago, I now have a very small bit of oil in the bilge, It looks like it is coming from where the cylinder head seams to the block. Is that possible if I need to tighten head bolts? How do you tigten head bolts?
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Old 11-26-2010
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In most cases you need a manual as there is a sequence.Also need a torque wrench.This is sometimes required with new/rebuilt motors.marc
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Old 11-26-2010
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With a wrench...

What makes you think the oil is coming from the cylinder head? Leaks can be funny things, and may not always be coming from where it first appears to be.

Quote:
Originally Posted by puff6022 View Post
I have a Yanmar 2GM20F, I had it rebuilt a few years ago, I now have a very small bit of oil in the bilge, It looks like it is coming from where the cylinder head seams to the block. Is that possible if I need to tighten head bolts? How do you tigten head bolts?
Thanks
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Old 11-26-2010
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Regarding the sequence, you start in the center, and work your way to the edges. The manual will tell you what the spec is.

MOST likely the leak is NOT the head bolt torque. More likely the valve cover gasket. You need a torque wrench and, possibly, a new valve cover gasket to fix.
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You can ruin a valve cover if too tight.Spreads it.re torque wrench mentioned above.marc
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Old 11-26-2010
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First step would be to replace the valve cover gasket-that's more likely where the oil is coming from, and its easier to do.
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Old 11-26-2010
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Be aware that many modern engines have head bolts that are designed to be tightened to the point where the bold stretches (elastic deformation) to the point that if you remove the bolt and compare it with a new bolt, the old bolt is longer. In other words, if you need to tighten the head bolts, you will need a new set. I do not know if this is true for Yanmar engines. If you are going to replace the valve cover gasket, consider this product: Permatex Hylomar Universal Blue Racing Formula Gasket Dressing & Flange Sealant available at your local automotive parts store.

Yanmar Manual (operation manual, does not include major engine work, click on page number in table of contents for that page of the manual)

1GM10-3HM35 SERVICE MANUAL (about $95, but necessary if you do any engine work, find it with Google)

I have been disappointed with Clymer manuals for automobiles and trucks. Maybe the boat engine manual would be better, but do not buy without inspection first. Usually these books have little information on a particular engine and pad books with very generic descriptions on maintenance.

For general information about diesels: Marine Diesel Engines: Maintenance: Troubleshooting, and Repair by Nigel Calder

For a simpler book for general information on diesels: Troubleshooting Marine Diesels by Peter Compton

Last edited by LakeSuperiorGeezer; 11-26-2010 at 11:08 AM. Reason: Referenced specific web sites that sell products
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Old 11-26-2010
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The problem is most Yanmar manuals is although they do list the torque specs. and sequences they do not itemized if this is an 'unlubricated' or lubricated (30 wt. oil, etc.) torque value nor if this is a 'once and done' torquing or is a sequence/repeat (3X) torque .... quite primitive in comparison to most current 'automotive/truck' specs. on torquing. Obviously, no mention of 'stretch bolts' is noted.

So, with the absence of 'clarity' of values, I usually 'dry torque' 3 times when working on older Yanmars - as that usually tends prevent 'warpage' even though I may be over torque-ing.

The best for Yanmars is to obtain the "Service Manual" for each particular engine model ... although there still remains a lot of "Japlish" words in the translations.
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Looks Like Good Advice to Me

Quote:
Originally Posted by RichH View Post
The problem is most Yanmar manuals is although they do list the torque specs. and sequences they do not itemized if this is an 'unlubricated' or lubricated (30 wt. oil, etc.) torque value nor if this is a 'once and done' torquing or is a sequence/repeat (3X) torque .... quite primitive in comparison to most current 'automotive/truck' specs. on torquing. Obviously, no mention of 'stretch bolts' is noted.

So, with the absence of 'clarity' of values, I usually 'dry torque' 3 times when working on older Yanmars - as that usually tends prevent 'warpage' even though I may be over torque-ing.

The best for Yanmars is to obtain the "Service Manual" for each particular engine model ... although there still remains a lot of "Japlish" words in the translations.
The only thing I can add is make sure the threads are clean. You should be able to screw the bolts in by hand to the point where they bottom in the block without the head on. If you run a tap as a thread chaser for cleanup, be sure to blow out with compressed air, or at least with one of those cans for blowing dirt out of a computer keyboard. I do not think you can over thighten the bolts since what you are concerned with is whether the threads can withstand the torque (do not over tighten with a torque wrench), not how tight the head is pulled down onto the block. Also consider the cheaper spring type torque wrench, as I have seen the clicker type give inaccurate readings. However, with the spring type, you have to be careful to bring the pointer up to the required reading, there is no automatic click indicating the correct torque, and they cannot be used in tight quarters where you cannot see the dial or pointer.
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Old 11-26-2010
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Head bolts should always be tightned in steps, I normally use 1/3 of the final setting for the first step, 2/3 for the second and the final speaks for itself. If the headbolts are tightened to the final setting on the first go, expect trouble. That's not a spec sheet talking, that's many, many years of rebuilding engines of all sorts.

As far as sequence goes, in the absence of any absolute instructions from the maker, start in the middle and work outwards (as mentioned in an earlier post) but try and remember to do this in a circular pattern as well as working outwards.

Watch this video YouTube - How To Torque Cylinder Head Bolts and if you want to cut to the quick, go to minute 16 which is where the fellow expalins the tightening sequences etc.

Normally stretch type bolts have a torque setting then a further graduated turn. The spec sheet will say something like "75Nm then 3/4 turn further". I don't believe Yanmar are stretch type bolts but the specification will give a clue to that.

And I also don't believe that re-tightening a cylinder head that has been run for a time will have any effect. The bolts will have "siezed" and the torque setting will be reached long before the bolt moves (unless the bolt is loose but then you will have bigger problems than an oil leak)

Just my opinion but ike I said, born of many engine rebuilds over the years.
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