GPW Engine rebuild - crankshaft issue

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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YLG80
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Re: GPW Engine rebuild - crankshaft issue

Post by YLG80 » Sun Nov 15, 2015 12:55 pm

Hi Gindi,
I'm thinking to your project while working on the engine :) !
I would be curious to know if you plan to do that with a CNC machine or not.

I've already made two sets of steel shims: 0.002'' and .003''
They are cut to fully cover the bearing cap seat.
0.003" shims looks good with a clearance of .002'' on bearing #2 and #3.

But I'm still waiting to test them with a new bearing set.
I've ordered a new .040 set from another source.

When we've made all the measurements, we've only checked the dimensions
The insert thickness was found correct at various positions.

But I suspect a little shape problem on the current inserts that I'm using.
That's difficult to measure though.(back light and ruler)
It looks like the cross section is not flat/straight at the oil holes level. (top external surface of the insert)
It's perfectly flat on both sides. (crushing ends)
I believe that these holes were punched in the manufacturing process which can be seen through the hole section.
This could have slightly distorted the materials.
This could have no effect if the inserts are crushed enough in their seats.
The old inserts were deburred using a drill after punching.
With the same measurement method they look absolutely flat.
But they remained crushed during years in my engine!

I'll see with the other inserts set.
Yves
Last edited by YLG80 on Mon Nov 16, 2015 11:13 pm, edited 2 times in total.
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Re: GPW Engine rebuild - crankshaft issue

Post by Joe Gopan » Sun Nov 15, 2015 1:44 pm

How come you are avoiding Line boring?
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Re: GPW Engine rebuild - crankshaft issue

Post by YLG80 » Tue Nov 17, 2015 4:55 am

@Joël
How come you are avoiding Line boring?
Because it's an interesting technical challenge.
I guess I will be able achieve again what was done during the last overhaul in the fifties.
And finally, because I do not want to take risks with my engine block.
(crankshaft centerline modified, timing problems and other joyousness like this.)
I've even read somewhere on the G about a rare Wilson block ruined during a line boring process.

Regarding the inserts wall thickness, I've computed the thicknesses for each oversize shell.
(attached file - crankshaft and rod bearings) This is based on specs found in the King bearings catalog.
Don't forget that the oversize value refers to the crankshaft or rod diameter.
To calculate the correct value for a shell, you have to divide the oversize value by two before adding it to the STD wall thickness dimension.
I've checked my crankshaft (0.040'') and rod (0.050'') against that table and they are correct.
Hope it will help people, like me, struggling with bearings.
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Re: GPW Engine rebuild - crankshaft issue

Post by Joe Gopan » Tue Nov 17, 2015 5:31 am

If the Main Bearing bores in the block are not correct and in perfect allignment,it will be reasonable to expect a repeat performance of all that went wrong in the first place. Jeep engine assembly is quite simple and pretty straightforward. Attempting to compensate using shims and off the wall technique is inviting more of the same.
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Re: GPW Engine rebuild - crankshaft issue

Post by artificer » Tue Nov 17, 2015 8:05 am

Frankly I wondered why the seeming obtuse question when Yves has told us what he is planning & why.

All I have read into this so far is:
Because someone has slightly altered 2 main bearing caps previously Yves is now contemplating shimming these 2 bearing caps to maintain their circle with the engine block.

There has been nothing about the bores in the engine block being out, as I recollect.

Trying to call wolf is not helping anyone, so let Yves get on with his plan & tell us what he is obtaining @ each step.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
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Re: GPW Engine rebuild - crankshaft issue

Post by Bill H. » Tue Nov 17, 2015 12:38 pm

Yves, my suggestion is please don't screw around with placing shims to offset a machining error. You run more of a risk destroying this block by playing with shims than you do line boring and getting it right the first time. If you don't have a competent machinist (and from what you have posted you don't) send it away and get it done right and never worry about it again. You are conversing with the best in the business right here in this thread. Listen to them, please. JMHO.
Bill H.

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1953 Willys M38A1
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Re: GPW Engine rebuild - crankshaft issue

Post by Joe Gopan » Tue Nov 17, 2015 1:54 pm

artificer wrote:Frankly I wondered why the seeming obtuse question when Yves has told us what he is planning & why.

All I have read into this so far is:
Because someone has slightly altered 2 main bearing caps previously Yves is now contemplating shimming these 2 bearing caps to maintain their circle with the engine block.

There has been nothing about the bores in the engine block being out, as I recollect.

Trying to call wolf is not helping anyone, so let Yves get on with his plan & tell us what he is obtaining @ each step.
__________________________________________________________________

If the Main Bearing caps are being shimmed to fit the block or the crankshaft, this means that the "housing bores" must not be correct. "Housing Bores" are the three different inner diameters of the block at the main bearing journal locations. Simple as that.

QUOTE JEEP FACTORY SERVICE MANUAL:
"Never file either the bearing cap or the bearing to compensate for too much clearance. Doo not use shimsunder a bearingcap or behind a bearing shell."
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Re: GPW Engine rebuild - crankshaft issue

Post by artificer » Tue Nov 17, 2015 2:44 pm

Actually knowing how to fix/correct things comes with practice & experience using tools of the trade [this includes common sense].
1. If the engine block tunnel bore is correct & in line nothing relating to the engine block casting needs attention/altering.
2. We have been told someone [who shouldn't have] minimally filed only one side of the original middle & rear main caps, so these caps need correcting.
3. That can be done in more that one way & achieve identical results.
One method is inexpensive, the other very expensive.
ensuring the filed portion side is perfectly flat [as Gindi added] one replaces the amount removed using a suitable shim on that side to re-establish each crankshaft bores/bearings concentricity.
[ii] building up the caps to replace the material removed then machining or if enough material is available machine both of the altered caps ends flat. Then assemble & line bore to ensure all the cap circles fit perfectly with the unchanged engine block bore.
3. I suggest that Yves go ahead with his plan to use a correct thickness shim on each of these 2 caps to re-establish their perfect circle with the main bearing tunnel.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: GPW Engine rebuild - crankshaft issue

Post by Tony W » Wed Nov 18, 2015 1:58 am

I,m With Bill H on this
I can see this ending in tears.
Shimming ,in my humble 43 tears engine rebuilding experience is not the way to go.
If your Wilson block is so precious, find a better rebuilder and do the job right the first time.
Tony
GPW Feb, 45,
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Re: GPW Engine rebuild - crankshaft issue

Post by Chuck Lutz » Thu Nov 19, 2015 7:27 pm

Yves....

Why not buy a pair of rods and caps that haven't been butchered and forget about line boring and shims?
Chuck Lutz

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Re: GPW Engine rebuild - crankshaft issue

Post by Bill H. » Thu Nov 19, 2015 7:41 pm

Chuck Lutz wrote:Yves....

Why not buy a pair of rods and caps that haven't been butchered and forget about line boring and shims?

Chuck, you can not mix and match main bearing caps. Buying caps is an option but it would have to be line bored even more so than using the old caps and shimming.
Bill H.

"Each shall seek his own kind, in other words, a bird may love a fish but where would they build a home together?" Tevye, Fiddler on the Roof

1952 Dunbar Kapple M100
1953 Willys M38A1
1962 AMC M422A1
1965 Stevens M416B1 X 2
1967 Kaiser M715

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Re: GPW Engine rebuild - crankshaft issue

Post by Joe Gopan » Fri Nov 20, 2015 4:41 am

I use the Federal Mogul Engine Bearings Shop Specification Manual for the housing bore I.D. in the block for Main Bearing Journals.
The tolerances for the three journals for Jeep are 0.0005", Dodge is 0.0005", GMC is 0.0010"
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Re: GPW Engine rebuild - crankshaft issue

Post by Joe Gopan » Fri Nov 20, 2015 6:39 am

That clearance is listed by Jeep as 0.0003 to 0.0029" and Federal Mogul as 0.0008" to 0.0029" ARMY TM for M38/M-38A1 lists 0.001"-to 0.002" on new parts.
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Re: GPW Engine rebuild - crankshaft issue

Post by artificer » Fri Nov 20, 2015 7:44 am

Rule of thumb for bearing clearances is 0.001/1" of diameter which is similar to 0.01/10mm.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: GPW Engine rebuild - crankshaft issue

Post by Chuck Lutz » Fri Nov 20, 2015 8:39 am

Bill...right, no swapping main bearing caps...I was talking about RODS and ROD CAPS which is a distinct option on the OTHER thread about double stacked rod bearings....not this thread. Just mixed up which one to post on.
Chuck Lutz

GPW 17963 4/24/42 Chester, PA. USA 20113473 (USA est./Tom W.)
Bantam T3-C 1947


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