chain vs gear driven block

1945 - 196*, Willys CJ series, questions, discussions, regarding anything related to the post war jeep.®
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Fuzzy
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chain vs gear driven block

Post by Fuzzy » Thu Jan 05, 2017 9:54 am

Can I use a 641087 block to build a chain-driven engine? Are there any modifications that need to be done, or can the 638632 block and 641087 block be used interchangeably for a chain-driven setup?
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Re: chain vs gear driven block

Post by Sean Collins » Thu Jan 05, 2017 12:28 pm

Fuzzy wrote:Can I use a 641087 block to build a chain-driven engine?
Yes.
Are there any modifications that need to be done
No, but you have to use chain-drive components: camshaft, oil pump, timing cover, and of course timing chain & sprockets.
or can the 638632 block and 641087 block be used interchangeably for a chain-driven setup?
Yes, as above.

638632 "CC" blocks are gear drive, 638632 w/no "CC" are chain drive.
 

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Re: chain vs gear driven block

Post by Fuzzy » Thu Jan 05, 2017 2:48 pm

Perfect. Thanks Sean.
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Re: chain vs gear driven block

Post by Wolfman » Sun Jan 08, 2017 6:41 am

So the 641087 block is a gear drive block ??
Would you need to block the gear oiler nozzle port when converting to chain ??
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Re: chain vs gear driven block

Post by Bruce W » Sun Jan 08, 2017 10:05 am

Wolfman wrote:So the 641087 block is a gear drive block ??
Would you need to block the gear oiler nozzle port when converting to chain ??
I wouldn't think so, unless it's actually in the path of the chain. It could still be used to lube the chain & sprockets, and I think it would do a better job than the hole thru the crank and sprocket that the chain-drive engines used. BW
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Re: chain vs gear driven block

Post by Wolfman » Mon Jan 09, 2017 6:00 am

The chain track would be the most concern. No doubt the oiler nozzle would do a better job of lubrication.
I'm thinking.
The cam and crankshaft are centered in the same location for both chain and gear drive.
With the gear drive, the crank gear and cam gear are a larger diameter than the crank sprocket and cam sprocket on a chain drive installation so the gears mesh together. The oil nozzle is positioned above the crank gear.
The crank sprocket and cam chain sprocket are smaller in diameter than the gear drive gears so the chain track would be closer to the center line of the crank and cam and closer to the oil nozzle position.
??????????
Just thinking on line.
Some times I think too much.
Guess it is all irrelevant. If the nozzle was in the way of the chain, it would become obvious pretty quick. :roll:
Be nice !
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Re: chain vs gear driven block

Post by Bruce W » Mon Jan 09, 2017 8:52 am

Me too Mike, just thinking. I don't think I would use both oiling methods, if the nozzle works, I'd block the passage in the crank. BW
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Re: chain vs gear driven block

Post by athawk11 » Mon Jan 09, 2017 10:14 am

Based on the photos, I think the oiler would conflict with the chain. This passage could be plugged, but...

Does a gear drive crank shaft have the oiler passage? If not would you need a chain drive crank?

Image

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Re: chain vs gear driven block

Post by Wolfman » Tue Jan 10, 2017 6:21 am

I think the photos just answered this question.
Even if a new chain missed the oiler nozzle, the oiler is on the slack side for a chain drive set up and it would not be long before wear and chain slack would take the nozzle off the front of the block. Big oil leak and who knows where the nozzle might end up.
Block the oiler passage.
Don't think the gear drive crank is drilled. I always wondered how much good the passage did anyway ?? All the oil being returned on top of the timing cover should be sufficient. Unless there was not a filter and return line ??
I think the oil filter was an after thought and the passage was pre filter.
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Re: chain vs gear driven block

Post by Joe Gopan » Tue Jan 10, 2017 7:37 am

Even if the change could be done, there is a concern about an oil pressure drop at the front of the block.
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Re: chain vs gear driven block

Post by Wolfman » Thu Jan 12, 2017 4:57 am

I am a little slow sometimes but. Guess that fits in with the rest of the responders. 8)
This going to be a non issue.
There is a difference in the height of the engine front plate.
The gear drive plate is taller than the chain drive plate.
With the chain drive, you will have to use the cover with the pin to hold the cam in place so you will have to use a chain drive front plate.
The chain drive front plate does not have a cut out above the crank for the oil nozzle so you won't be able to install a nozzle.
You will need to install a flat plug in the nozzle oiler hole so you can use the chain drive front plate.
Be sure to install an oil filter. The return is the only lube oil the chain will get since the gear crank is not drilled.
That was a long time coming !
Curious ? Why are you installing a chain drive in a geared engine ??
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Re: chain vs gear driven block

Post by Fuzzy » Thu Jan 12, 2017 10:48 am

I'm trying to get my MB engine rebuilt, but the shop found big cracks so they suggested a new block would be cheaper and better than a repair. Unfortunately wartime blocks in good shape ready for rebuild are not easy to come by, so I'm trying to see if a CJ block would work.
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Re: chain vs gear driven block

Post by Wolfman » Fri Jan 13, 2017 6:30 am

Got it.
If you go up to Athawks pictures, you will see what I am talking about.
One of his pictures shows a gear drive front plate on a chain drive block.
You can clearly see the hole in the front plate for the cam retaining plate is taller than the block behind it. There is an uncovered hole at the top of the cam retaining plate hole in the front engine plate..
Going the opposite way as you are after, a chain front plate on a gear drive block will work because the round hole for the cam brass thrust washer will not leave that hole uncovered. The chain drive components on the gear drive block will work.
I have done this.
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Re: chain vs gear driven block

Post by Sean Collins » Fri Jan 13, 2017 8:09 am

Wolfman wrote: There is a difference in the height of the engine front plate.
The gear drive plate is taller than the chain drive plate.
No there isn't. They are both the same outer dimensions.
... so you will have to use a chain drive front plate.
Not so. EITHER front plate will work.
Be sure to install an oil filter. The return is the only lube oil the chain will get since the gear crank is not drilled
ALL crankshafts made up thru mid-Jan '48 were drilled for chain lubrication. As long as it has the annular groove on the nose shaft, it's good for chain timing.
 

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Re: chain vs gear driven block

Post by Sean Collins » Fri Jan 13, 2017 8:11 am

Fuzzy wrote:I'm trying to get my MB engine rebuilt, but the shop found big cracks so they suggested a new block would be cheaper and better than a repair. Unfortunately wartime blocks in good shape ready for rebuild are not easy to come by, so I'm trying to see if a CJ block would work.
Don't get sidetracked by the conjecturing. Your MB engine guts will fit right into a gear drive block w/out modifications.

Remove the gear squirt nozzle (if present) and plug the hole. The chain will receive its NORMAL FACTORY lubrication via the crankshaft drillings.
 


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