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07-06-2017, 07:13 AM
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#1
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Guru
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,146
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Lehman 120 head machining
Manual says not to machine head. Amercican Diesel I believe said up to 0.009.
Machine shop says way more (up to 0.040) typically done with no issues. Shop is very experienced in modifying gas engines for tacing but has good experience with marine diesels too.
Any experiences or strong opinions on head machining then the whole replacement process?
Other than super clean surfaces and dont use any abrasives to clean?
Anyone have this done or research it with different info?
Thanks....
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07-06-2017, 01:41 PM
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#2
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Guru
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,146
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Bump....any tips at all?
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07-06-2017, 02:07 PM
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#3
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Guru
Join Date: Jun 2008
Posts: 5,036
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I have no experience in that regard with this engine.
But......
I would ask ADC why THEY put the limits at .009".
Is it a clearance issue?
Does it change the compression ratio to where it over stresses the internals?
Etc.
They may have the "local knowledge" that the performance guys don't have about this particular engine.
How far out of flat is the head? Or are you anticipating?
__________________
Jay Leonard
Ex boats: 1983 40 Albin trunk cabin, 1978 Mainship 34 Model 1
New Port Richey, Fl
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07-06-2017, 02:16 PM
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#4
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Guru
City: Brookline, NH
Vessel Name: Shalloway
Vessel Model: Defever 44, twin Perkins
Join Date: Sep 2013
Posts: 2,260
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Quote:
Originally Posted by psneeld
Manual says not to machine head. Amercican Diesel I believe said up to 0.009.
Machine shop says way more (up to 0.040) typically done with no issues. Shop is very experienced in modifying gas engines for tacing but has good experience with marine diesels too.
Any experiences or strong opinions on head machining then the whole replacement process?
Other than super clean surfaces and dont use any abrasives to clean?
Anyone have this done or research it with different info?
Thanks....
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Here's my take on it: The factory says not to do it. Ok, why? Is it a clearance issue? A compression issue? A material thickness issue? Or maybe something none of us has thought of yet?
That said, unless one is trying to change compression or some other characteristic, its best to take off as little as possible. If .005 cant clean the surface and make it flat within spec, maybe its best to opt for a different head.
Ken
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07-06-2017, 02:16 PM
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#5
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Guru
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,146
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Anticipating, and wondering where ADC got the 0.009 when the manual they refer me to says no.
I have a feeling like many things Lehman, there has been evolution without written updates all located in one spot other than Brian now...though there are others familiar with Lehmans that have similar or even diffetent answers.
If the machine shop takes off more than what I am comfortable with, we will sit down and see just what the numbers wring out. They may be insignificant or to limit comoression, etc, I will put stops on the engine controls....or break down and buy another head.
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07-06-2017, 02:48 PM
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#6
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Guru
Join Date: Jun 2008
Posts: 5,036
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Quote:
Originally Posted by psneeld
Anticipating, and wondering where ADC got the 0.009 when the manual they refer me to says no.
I have a feeling like many things Lehman, there has been evolution without written updates all located in one spot other than Brian now...though there are others familiar with Lehmans that have similar or even diffetent answers.
If the machine shop takes off more than what I am comfortable with, we will sit down and see just what the numbers wring out. They may be insignificant or to limit comoression, etc, I will put stops on the engine controls....or break down and buy another head.
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I think you hit it on the head with the evolution theory.
We don't know but perhaps someone asked the Ford engine engineers what limits there were on machining a warped head (this happens often in eninge rebuilding) and being ultra conservative they responded with .009". They could NOT respond with a number that might not work, they had to give a number they were positive would be ok. Perhaps they even tested it. And maybe at the time that was enough to work and the question never came up again.
Some day we won't have the option of buying a new head, then what?
Yes we will machine the head .010" or whatever is necessary and using reasonable skills give it a go.
__________________
Jay Leonard
Ex boats: 1983 40 Albin trunk cabin, 1978 Mainship 34 Model 1
New Port Richey, Fl
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07-06-2017, 04:05 PM
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#7
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Guru
City: Boston
Vessel Name: Adelante
Vessel Model: IG 30
Join Date: Nov 2016
Posts: 1,609
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Manual doesn't say NOT do it, it simply says NOT RECOMMENDED.
Claims it might cause fowling between valves and pistons. I suspect Brian has sold enough head gaskets and heard enough anecdotes to feel comfortable with .009.
I'm guessing that engineers over designed the engine and if .009 will give you a flat head then go for it. The valves might protrude a little more into the combustion chamber so that might account for the potential fowling. .040 might also work, but clearly the less skim the better.
Have you measured the flatness of the head to see how much it's off?
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07-06-2017, 04:10 PM
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#8
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Guru
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,146
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Correct on the not recommended part, went back and reread it.
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07-06-2017, 08:35 PM
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#9
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Guru
Join Date: Jan 2010
Posts: 1,181
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Are the head gaskets on these engines composite or just steal. It would not be unrealistic to stack two steel head gaskets on top of each other
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07-06-2017, 08:50 PM
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#10
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Enigma
City: Slicker?
Join Date: Oct 2007
Posts: 16,563
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Greetings,
Mr. 30. Stack 2 head gaskets? I know this is acceptable with some gasoline engines but I really don't know if it would work with the much higher compression ratios of a diesel. Maybe one could find/make/have made a single thicker gasket???? Beyond my technical knowledge for sure...
__________________
RTF
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07-06-2017, 09:51 PM
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#11
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Guru
City: Sydney
Vessel Name: Sojourn
Vessel Model: Integrity 386
Join Date: Oct 2011
Posts: 13,329
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Quote:
Originally Posted by motion30
Are the head gaskets on these engines composite or just steal. It would not be unrealistic to stack two steel head gaskets on top of each other
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Just what I was about to suggest, as a cure if the head planing threw up problems.
It`s not like the Ford Lehman has domed pistons likely to collide with 4 valves per cylinder driven by quad overhead camshafts.
__________________
BruceK
2005 Integrity 386 "Sojourn"
Sydney Australia
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07-07-2017, 05:11 AM
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#12
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Guru
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,146
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Many advise not using regular rags to wipe things down because of dust and lint even for gas engine gaskets.
It would be hard to believe stacking 2 would be OK, especially with the metal ring around each cylinder.
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07-07-2017, 07:39 AM
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#13
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Guru
Join Date: Jun 2008
Posts: 5,036
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I would not use 2 gaskets.
I don't have the service manual available. What is the spec for flatness?
You may be within that right now and all this discussion is moot.
__________________
Jay Leonard
Ex boats: 1983 40 Albin trunk cabin, 1978 Mainship 34 Model 1
New Port Richey, Fl
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07-07-2017, 10:31 AM
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#14
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Guru
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,146
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Just talked to Bomac and they said 0.015.
More numbers....
Jay, couldnt find a spec because the manual I have says machining not recommended, and any bowing or warping, the head must be replaced.
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07-07-2017, 11:30 AM
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#15
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TF Site Team
City: Jacksonville
Join Date: Nov 2008
Posts: 11,681
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Quote:
Originally Posted by psneeld
Just talked to Bomac and they said 0.015.
More numbers.....
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Greg has probably rebuilt more Lehman's than anyone.
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07-07-2017, 12:02 PM
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#16
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Guru
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,146
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Just blows my mind how there is no definitive answers to some simple questions. Especially amongst the experts.
Sure after 50 years of changing specs, there might be some confusion.
Some enterprising person might do well with a Lehmans For Dummies Book....
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07-07-2017, 12:03 PM
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#17
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Guru
City: Brookline, NH
Vessel Name: Shalloway
Vessel Model: Defever 44, twin Perkins
Join Date: Sep 2013
Posts: 2,260
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Quote:
Originally Posted by psneeld
Just talked to Bomac and they said 0.015.
More numbers....
Jay, couldnt find a spec because the manual I have says machining not recommended, and any bowing or warping, the head must be replaced.
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The manual I have says the same thing. The concern stated in the manual is that it is possible for the piston to contact the valves, but obviously there must be *some* room and folks like Bomac must have a lot of experience in this. Do you know if your head is warped and if so how much?
Ken
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07-07-2017, 12:06 PM
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#18
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Guru
City: Ft Pierce
Vessel Name: Sold
Vessel Model: Was an Albin/PSN 40
Join Date: Oct 2011
Posts: 28,146
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Waiting for the machine shop report.
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07-07-2017, 12:20 PM
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#19
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Technical Guru
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
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Should be no issue shaving the head. It won't change compression as the thing is flat anyway.
The thing that changes is valve face position. If you shave the head the valves will now be closer to the pistons. On non-firing TDC, both valves are cocked open slightly and they are very close to piston.
In the manual there should be a spec for valve face depth WRT head deck. If after the shave that number is out of spec, the valve seats need to be ground a little to get it in spec.
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07-07-2017, 12:22 PM
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#20
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Valued Technical Contributor
City: Litchfield, Ct
Join Date: Aug 2012
Posts: 6,784
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Milling the head will have negligible effect on compression. But if you take off more than 0.009" or maybe 0.015 if you believe Bomac, then I do believe you have a risk of valves interfering with the piston. The consequences will not be good.
You could put a little putty on the top of the piston on one cylinder and lightly oil the valve head to keep it from sticking, assemble and tighten the head and then rotate the crank, remove the head and check the clearance. The putty should have depressions made by the valve heads and you can cut a groove with a razor blade to see how much putty is left.
David
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