Civi crank in GPW

1941 - 1945, MB, GPW modifications, sugestions, and ideas, official MWO's and unofficial WWII field mods NO EBAY or COMMERCIAL SALES.
Lew Ladwig
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Civi crank in GPW

Post by Lew Ladwig » Fri Mar 30, 2007 8:36 pm

After consulting with several smart folks I believe the sweet trick in a gpw rebuild is to install a crank out of a 2a. A little clearence inside the block needs to be done and the chain gets lubed by the oil return. Now I don't have a good 2a crank but I do have an Fhead crank. Can that be used or is it different?
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Post by iron duck » Fri Mar 30, 2007 9:42 pm

Dear Lew,

I see no reason to install a 2a cranckshaft in a GPW.
The only good I can see would be the changeover from chain to sprockets for the camshaft thrust.
But Richard Sanders makes now wonderfull chains for that aplication. They allows us to use all the original parts without the bad dist chain.
My opinion is, leave the engine in its original configuration with original cranckshaft.
Use hardened valve seats, cilindersleeves, and a Richard Sanders dist chain.
You will have a very good reliable engine.
If you want to go a step further, a CJ oilpump gives a better oilpressure, but someone can see that it is not an original pump.

Best regards, Luc

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Post by Glen » Sat Mar 31, 2007 5:24 am

If you ever compared a CJ2A crank to the earlier MB/GPW, you would see that the counterwieghts are much bigger making for a smoother engine. Connecting rods too. The CJ2A crank will take either chain and sprockets or gear drive. CJ2A cranks are alittle more available. Flywheels will change no problem, taking note of the either two taper or shouldered index bolts. The block will require alittle relief in acouple of places.

F134 cranks should work also with the same type of fitting. If you are rebuilding an MB/GPW engine and are needing to replace the crank, I would go the later crank........

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Post by Lew Ladwig » Sat Mar 31, 2007 7:02 am

Glen,
That is what I was told about the 2a crank. I was not sure about the fhead crank. Is there any fundamental difference between the two cranks?
Lew

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Post by Glen » Sat Mar 31, 2007 8:55 am

No, they use the same pistons, rods, etc. There may be a difference in the two index bolts. They may be straight shouldered instead of tapered. As I recall, the taper bolts can transfer to the "new" crank. Other than that, is should work like a champ.

I had a friend who rebuilt his MB engine top to bottom. He used a CJ2A crank and rods. As I recall, he had to make clearance on a oil galley plug on the block and something about one rod. The "new" crank had the straight index bolts so we used a matching flywheel which was also 97 teeth. The big mod was the installation of a thrust plate for the cam so he could use gears instead of sprockets and chain. If you use sprockets and chain, you won't need to mess with this. His came out very good.

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Post by iron duck » Sat Mar 31, 2007 11:01 am

"If you ever compared a CJ2A crank to the earlier MB/GPW, you would see that the counterwieghts are much bigger making for a smoother engine."

Glen,

I noticed the diference between both cranckshafts.
I always wondered why CJ's used those bolt on type counterweights. Something to do with cheaper way of manufacturing ?
A heavyer or different shaped cranckshaft could be cast also I guess.
Never compared weight between both, but you are probably right.
Where did you get that info ?
Or did you just tried it out ?

My point is that a MB or GPW engine just works fine as is.
But of course, a cranckshaft is not visible, and if giving a better or smooter result someone can switch over without any problems.

Best regards, Luc

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Post by Glen » Sat Mar 31, 2007 2:46 pm

I have seen acouple of old non-military manuals that covered the subject. This must have come up in the 50's or 60's when an older engine had to be rebuilt using newer parts.

Why the counterwieghts are bolted on is beyond me.

I can tell you a friend of mine totally rebuilt his MB engine using the CJ2A crank and rods. There was a noticeable difference in smoothness. From the outside of the engine, you can't see the difference, it's all internal.

Ready-to-go CJ2A crank "kits" with matching bearings are fairly easy to find. Good machine shops to turn and balance a crank are not. Same as boring (and possibly resleeving) the cylinders and using say TRW or Moog pistons or bearings on the mains and rods. I think it is more important to do the job right and with quailty parts more than anything else. I personally have never been into an M38 or M38A1 engine but I would not be supprised to see the same type of CJ2A crank stock in those engines. I can tell you if you wish to convert from chain and sprockets to gear drive it is a pain (MB's use a spring loaded pin to hold the cam sprocket against the block, CJ2A's and up use a thrust plate bolted to the block behind the cam gear to hold the cam in place) and you will need a good machine shop to help do the work.

Oh, one more thing, if you are using the military manual to setup the rods, BEWARE, there is a typo in most manuals. Rods have a short and a long "skirt" down at the connecton bearing with an oil squirt hole on the short side. The short skirt/oil squirt hole must face the closest main bearing. That means rods #1 and #3 short skirt face forward, rods #2 and #4 short skirt face rearward. Look carefully and you will see what I mean. The closest picture I can refer you to is out of TM 9-803, Section 51. Many times I have seen these installed incorrectly and ruin the rods and crank.

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Post by iron duck » Sat Mar 31, 2007 10:29 pm

"Oh, one more thing, if you are using the military manual to setup the rods, BEWARE, there is a typo in most manuals."

Glen,

I noticed that too, bad thing is that it is possible to mis install them.
Someone can see that the rod is at one side of the piston center, engine shall work.
Question is how long I guess ??

I asked someone that is in the engine rebuild business all his life, and he duosn't know the answer on the bolted on counterweights either.
CJ cranckshafts better balanced than MB GPW cranck's ?
The MB manual says that it is balanced statically and dynamically.
Well, I guess that a CJ cranck is an improved cranck and has a better result when installed then a MB cranck is the truth.
I would love to know what and why ....

Thanks, Luc

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Post by iron duck » Sat Mar 31, 2007 11:39 pm

I just got a friend on the phone that is involved with mechaniques with all his hart.
We discussed the bolted on versus cast counterweights.

He thinks that it has both economic and technic improvements.
Economical : the counterweights can be made of inferiour metal instead of the high quality metal the cranckshaft is made from.
Loocking at the time CJ's were made we know that materials were scarce.
Technical : another reason he can see is that a big piece of unbalanced metal is much more difficult to keep vibrations low than a lighter one during finishing.

I can live with that explanation, but still it is guessing.
I hope someone else shims in with more knowledge to confirm or put in question.

Luc

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Post by sergio » Sun Apr 01, 2007 4:53 am

No doubt you can achieve better balance with a 2A crank but, to me, the unique state of balance of a particualr engine is part of that vehicle's experience. If you want to know what it was like for soldiers to ride thousands of miles in an MB or GPW, you need to have that little hand numbing, spine tingling vibration to accurately experience it. Balancing your L-134 until it feels like an electric motor isn't part of the WWII experience.

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Post by petesilfven » Sun Apr 01, 2007 9:31 am

I dont think anybody will EVER get a jeep engine as smooth as an electric motor. :lol:

If you're going to use a late crank, get it Magnafluxed and tell the operator to pay attention to the welds between the counterweights and the crank cheeks. I have seen many with cracked welds, and one where the counterweight came off while running. They can be repaired by grinding out the weld and rewelding, preferably by a professional welder using the TIG process.

Anytime a crankshaft/flywheel assembly is changed from a factory assembly, the shoulder bolts should be installed in place of the tapered ones. Assemble with the 4 conventional bolts, drill out the two holes with a 35/64 drill bit, and ream to size with a 9/16 chucking reamer. I use a magnetic drill press (portamag), and set it on the flywheel face with the crankshaft vertical.
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Post by Tinker » Mon Apr 02, 2007 10:30 am

Thought i'd jump in here....
I have a CJ crank in my MB and weight matched rods and pistons. The difference is impressive between this one and my GPW with an original crank. It's flat-out smooth. If that's your goal I think you'll be happy.

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Post by Lew Ladwig » Sat Apr 14, 2007 10:35 am

Ok, I found a 2a crank. The bolt up to the fly wheel is the same. The size of the counter weights is much larger. I have checked and she clear the inside of the block just fine. I just need to be sure the oil galley plug is a flush mount one. All of the oil passages are the same. The crank timing gear mounting area is all the same. It was a good thing I thought about doing this as while I compared the two cranks I noticed the gpw one has a bad score on #4 rod. Some folks have said I will not be getting the original jeep experience if I do this modification. I have driven jeeps with both types of cranks and the only difference I can tell is the cj crank has a touch more power, idles a tad smoother, but seems to accelerate 10% better. My jeeps are not parade queens, I like to drive them everywhere so I do want to get what I can out of them. I am very picky on my restorations and those who have seen my '47 will tell you that. This jeep is going to be given to my dad who will have to pull out onto the Olympic highway on a regular basis so I want to give him all she can do to get up to speed. I think this will work well.
Lew

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Post by iron duck » Sat Apr 14, 2007 10:40 pm

Dear Lew,

Did you already assembled the engine to running order with a CJ cranck, or do you still have to do it ?
It would be good if someone that freschly did the transformation made an acurate list from the mods required.
I have done it about 10 years ago, and remember that few things have to be done that require the right tools and experience.

Best regards, Luc

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Post by Lew Ladwig » Sun Apr 15, 2007 6:03 am

Lluc,
I just fitted the crank to make sure it had correct clearance of the counterweights. I have yet to do the machine work.
Lew


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