GPW Engine rebuild - crankshaft issue

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

Post by YLG80 » Tue Oct 27, 2015 7:58 am

Can't blame the machinist? Why not; it is his responsibility to get the grind right. That is why I pay them.
Are you prepared to discuss at the fourth decimal ?
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Re: GPW Engine rebuild - crankshaft issue

Post by artificer » Tue Oct 27, 2015 9:03 am

Yves wrote:There are indeed radius near the edges on the crank journals.
There should always be a radius [not too much though] & it is meant to be there....if not enough that can contribute to breaking a crankshaft.

Check & do figure 14 in this presentation for us please.
http://www.autozone.com/repairguides/Do ... 52800879af

It is checking tunnel bore alignment.
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Re: GPW Engine rebuild - crankshaft issue

Post by YLG80 » Tue Oct 27, 2015 10:39 am

Nice test... but I had to ask my wife to help me :) !
I did the test with a precision metal ruler and feeler gauges.
3 measurements :
First at the level of the 3 pins at the bottom of the bore
Second and third at the level of the interface between the block and the caps.

The 0.002'' (0.0508mm) feeler gauge does not pass through @ #1, #2 and #3.
Sorry there is no 0.001" in that set.
That's odd.
Not sure, but I believe a read somewhere that the 3 bores had different sizes, isn't it?
Larger going forward from #1 to #3, if I remember.
If it has been bored to #1 dimension, that would explain why #2 and #3 bearings are so tight.
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Re: GPW Engine rebuild - crankshaft issue

Post by Marty, SoCal » Tue Oct 27, 2015 10:41 am

Will the crank rotate in the block if you leave the middle bearing shells and cap off? (Torque the outer caps to spec)

If so, use a dial indicator on the crankshaft and see if the middle journal has any movement as you rotate the crank, (IIRC, the spec is .001")

Any run out on the center journal would indicate a bent crankshaft, which will also cause a bind.
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Re: GPW Engine rebuild - crankshaft issue

Post by Marty, SoCal » Tue Oct 27, 2015 11:06 am

A ground off-center crank may not bind. (It will be out of balance) but a bent one or one where one main journal was ground out of line with the others sure will.
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Re: GPW Engine rebuild - crankshaft issue

Post by YLG80 » Tue Oct 27, 2015 12:08 pm

@Marty
I cannot make the proposed test because if I torque #3 bearing, the crank will be seized.
As Gindi wrote, that's enough for me.
I will return the engine to the shop and ask them to find what happens.
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Re: GPW Engine rebuild - crankshaft issue

Post by YLG80 » Tue Oct 27, 2015 1:19 pm

Let us know what happens please.
Ok I'll do.

I almost sure I've problem B !
out-of-shape-crankshaft-journals.jpg
out-of-shape-crankshaft-journals.jpg (52.21 KiB) Viewed 1140 times
But don't know how to solve that issue. Polishing?
I would not like to have the crankshaft reground to the next undersize.
We will see.
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Re: GPW Engine rebuild - crankshaft issue

Post by YLG80 » Thu Oct 29, 2015 11:01 am

Today I paid a visit to the shop with the engine and the crankshaft parts.
The motorist who worked on my engine was there.
After having examined the #2 and #3 bearing inserts he agreed that there was a problem.
He did not agree with the solution to put shims under the caps. Good, my business was well engaged :) !
He confirmed that the journal diameters were slightly on the high side. (As Joël suspected)

According to him, the only way was to rework the crankshaft journals manually :o .
He installed the crank on a V shaped support.
Then he took sand paper strips (360 or 380 grit) and kind of a long flat lace of about 1cm wide.
He then lubricated the journal and the paper (WD40).
Then, he wrapped the sand paper strip around the journal and wrapped the lace around.
He started to pull each lace termination. Surprising !
He did that during a while until his face got red :oops: !
Then he told me to do it myself !
It's very easy to do. It took about 10 min. per journal with 3 sandpaper strips.

He gave me a few strips to continue the job on both journals.
Then he measured the journals diameter and told me that now it should be OK.
We (I would say, I) got nearly .01mm which looked enough for him.

After a thorough cleanup, I've reassembled the crank and the bearings and torqued them.
And believe me, it was OK!
I can turn the crank easily with a wrench on the crank nut.
Although when I stop turning the crank, it sticks before I can turn it again.
He told me that I could do it once again at home to be sure to have the correct oil clearance.
He also advised me to finish the job with the a narrower sand paper strip to create kind of crossed lines on the journals.
I guess the finish has to look like the new cylinder sleeves.

Although it's easy, I hope I will not have the same problem with the rod bearings :) !

Returning home, I've searched for that method on Internet and I've found that picture in Google scanned book.
It looks like that method is or was widely used to polish cranks. I like that :) !
Here is the picture I've found.
crank_lace_polishing.jpg
crank_lace_polishing.jpg (94.07 KiB) Viewed 1244 times
Tomorrow I will check again if the crank does not stick too much and polish it.
I'm curious to retest the crankshaft with plastigage after that rework.

I'm happy with that cheap and clever solution (0.00€) !
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Re: GPW Engine rebuild - crankshaft issue

Post by Chuck Lutz » Thu Oct 29, 2015 11:39 am

I think it might be time to consider finding another machine shop and possibly another crankshaft.
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Re: GPW Engine rebuild - crankshaft issue

Post by YLG80 » Thu Oct 29, 2015 12:44 pm

Yves, That's the worse thing that could happen.
No problem for the messenger.

What happened to my crankshaft?
Why is that touch up method so bad for my crank?
We are talking about less than 0.01 mm in a 1942 engine.

"...find another machinist"

Sorry, I'm not prepared to throw away another 250 eur ++ on that crankshaft.
Last edited by YLG80 on Thu Oct 29, 2015 2:27 pm, edited 1 time in total.
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Re: GPW Engine rebuild - crankshaft issue

Post by Joe Gopan » Thu Oct 29, 2015 12:53 pm

Crankshaft polishing is more efficient and precise when the spinning shaft is polished using the crankshaft grinder. It appears your machinist is more blacksmith than machinist.
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Re: GPW Engine rebuild - crankshaft issue

Post by YLG80 » Mon Nov 02, 2015 7:32 am

I'm currently abroad on holiday's.
I'm trying to summarize what I've learnt about the dimensions.
Next week we will perform a complete measurement of the crankshaft related parts.
This will be with a good friend of my son (farmer).
He is working in a large garage for tractors and is allowed to borrow the calibrated instruments when the garage is closed.
He is used to work on very old tractor engines as well as ultra modern ones.

In the meantime, I' m questioning myself on a tolerance question based on the dimensions received in this post:
Bore #2 : 2.4895''/2.4900''
Journal : 2.2931''/2.2941''
Bearing insert #2 (+0.040'') thickness: 0.1173''

Let's assume that the crankshaft journal is at the minimum tolerance i.e. 2.2931''
I add 2X the bearing insert thickness = 0.2346''
Total : 2.2931'' + 0.2346'' = 2.5277''
This is way above the max. bore diameter of 2.4900''.
What's wrong in my calculation?
If I assume I have a crankshaft undersized to .050, then it fits with the same +0.040 insert thickness. Confused.
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Re: GPW Engine rebuild - crankshaft issue

Post by YLG80 » Thu Nov 12, 2015 7:57 am

We’ve found the culprit !
It took us a while to make so many measurements in that garage. (Each measurement several times)
I have an Excel spreadsheet with 3 tabs full of data.

Crankshaft main bores:

For some reason, bearing caps #2 and 3 have been filed down in the past! Oil pressure problem, incorrect shells?
Bore #1 remains intact. It reminds me that the machinist had found that two journals had been grounded to a different size.
We’ve measured the bores North-South and East-West with a telescope and a micrometer (M&W).
Both East-West measurements for bearing caps #2 and #3 are within spec (high side).
Bearing cap # 2 North South is missing 0.0033’’
Bearing cap #3 North South is missing 0.0035’’
On the old bearings, we could clearly see the grinding traces (crossed lines) as well as on the crushing edges of the inserts.
In fact the bearings inserts were also grounded flush with the caps!
I guess they have been filed down together.
The grinding traces are perfectly matching on the cap and the bearing shells.
Cap #1 has a totally different surface with original curved grounding traces.

I’ve only one picture of the engine just after removing the caps and while the upper bearings were still in place.
There is a trace of something grey/black color on the bearing cap interface.
It could be a paper shim as suspected by Gindi in his first post on that subject. I did not remark that.
cranshaft_bearing_2_paper_shim.JPG
cranshaft_bearing_2_paper_shim.JPG (73.96 KiB) Viewed 1125 times
Crankshaft journals
The crankshaft journals have been measured as follows: Edge-Center-Edge and 0°-120°-240°
Journals #1, #2 and #3 were grounded to the exact same dimension: 2.2940’’ / 58.27mm
Just at the maximum tolerance as mentioned before and we’ve not found any out of shape problem on the journals.
Packing seal was not polished by the machinist as remarked by Gindi : 2.3105’’ / 58.68mm
I will do that, and in the meantime, I’ve found an original Ford NOS box of 40 packing rear end seals FM-GPW 6702.
The one I’ve bought and placed before was way too thick!

Connecting rods:

The connecting rods bores have been measured using the same method:
They are all matching with the same size (brand new set): 2.0435’’. It looks OK.
The connecting rod journals were grounded -.050’’ @ : 1.889’’ / 47.98mm (high side no out of shape problem))
The insert thickness is 0.0756’’ so the clearance should be OK with about 0.0035’’ / 0.07mm.

Now my conclusions … for which I will likely be fired in flames again :oops: !

1-Never ask a machinist to simply grind a crankshaft.
It’s better to give him the block and the bearing caps and require him to match everything.
It’s sad, because he had my engine block on hand :( .
Or as advised by Gindi, perform a thorough measurement of each part and have the machinist to grind the crankshaft exactly to a required dimension.

2-As I do not want to deal with more problems and risks with a line boring, I will put correct shims back under bearings caps #2 and #3.
I will put 0.003’’ steel shims to recover the original bore shape (North-South size). It was just odd to put paper shims.
This should give an oil clearance of about 0.057mm.(calculation)
According to my son’s friend, there will be no problem with the bearing crush.
He told us that for such an old rugged engine, the crush height should be about 0.001’’/0.02mm to 0.002’’ / 0.05mm.
(for new high performance engines it can go up to 0.002’’ to 0.004’’).
As advised by artificer, I’ve measured the crush dimension and it was 0.004’’ per insert.
So with the shim, it will leave 0.001’’ for the bearing crush.
I will have also to order new bearing inserts, as he suspected them to have been over crushed and perhaps distorted.
Last edited by YLG80 on Mon Nov 16, 2015 8:16 am, edited 3 times in total.
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Re: GPW Engine rebuild - crankshaft issue

Post by YLG80 » Fri Nov 13, 2015 12:03 am

No, it seems that the block remains unchanged.
Only caps #2 and 3 have been filed down like this :
IMG_4868-grinding_traces-2and3.jpg
IMG_4868-grinding_traces-2and3.jpg (58.18 KiB) Viewed 1099 times
On the block side, the grinding traces are the same all the way through, parallel to the block axis:
crankshaft_block_line.JPG
(247.09 KiB) Downloaded 794 times
Starting from the front, each bearing cap contact face is slightly lower than the previous one.

Steel shims are rather easy to find, starting from 0.001", so I've ordered a shim stock set.
You are right, it's going to be a fine tuning.

Your project is very interesting and fascinating !
It reminds me a machine that I will see again in 2 weeks.
That giant machine bores and rifles a gun barrel of 6m length, straight! :o
Amazing, because it's a rather old machine and it works quite well ... without any laser pilot.
It drills the barrel at a speed of less than one inch per minute!
I'm not a mechanic, and I'm wondering how you will be able to line bore only the caps w/o any shift up to the block while progressing.
Taking your time as for the barrel, I guess.
Good luck also with your project !
Yves
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Re: GPW Engine rebuild - crankshaft issue

Post by artificer » Fri Nov 13, 2015 1:08 am

To do things like this properly:
If the block is in line [not forgetting each bore hole is slightly less in this engine] & the main bearing caps are out of alignment [modified/replacement/filed/altered caps won't fit properly & that is normal]....nothing needs to be removed from the engine block thus the timing chain [or gears] is a non issue.
Good [experienced] engine machine shops will add [weld] or remove material from the caps so that when they line bore to suit the good engine block nothing will be removed from the engine block, all will be hunki dori & just like straight from the factory.
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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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