Broken crank center main issue

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Model T Ford Forum: Forum 2015: Broken crank center main issue
Top of pagePrevious messageNext messageBottom of page Link to this message  By bob middleton on Thursday, March 05, 2015 - 12:36 am:

Ok friend got a block he thinking of selling center main is is little out due to broken crank he had otherwise its good shape just wonering if a shop would just repour the center main


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Thode Chehalis Washington on Thursday, March 05, 2015 - 12:59 am:

The block is cast iron and cast iron can not be a "little out". It has to be good or broke, cast iron does not bend. I'd check very well for cracks in center web of the block.

A machine shop can check it for cracks that will not show up just by looking at it.

Jim


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Thursday, March 05, 2015 - 01:18 am:

Jim - Bob's total lack of punctuation makes interpretation difficult, however, I think he means that the center main just has some damage to the babbit and the other mains are good. The only thing he mentions "broke" ( I think he means broken) is the crankshaft. He really doesn't say that there's anything wrong with the block.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Thursday, March 05, 2015 - 01:30 am:

Bob
Yes it can be done, BUT most shops won't want to, and it is probably false economy


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Thursday, March 05, 2015 - 01:31 am:

Re-pouring and machining just the centre main can be done but the replacement crank will need to be the same specs as the old one, or if the old one had been re-ground then using a stock one could allow for all 3 to be line bored.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Allan Bennett - Australia on Thursday, March 05, 2015 - 05:06 am:

I have just been through a similar situation. When my crankshaft broke just forward of the no 2 rod journal, the short front section of the crank suffered a big whack which ovalled the front main to such an extent that even a standard journal would still be too small. I could have another crankshaft ground to the exact same dimensions as the broken one. However, the gent who does the line boring of the mains was not prepared to do just the front bearing. He finds it too difficult with his machine to line up the bearing tunnels accurately enough to ensure a job he would be comfortable with doing.

So I am having all new main bearings, to match the newly ground crankshaft with a minimal amount taken off the mains, and the same rod journals as before. This also means that we start with a new slate getting the end float of the crank set.

Allan from down under.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kohnke Rebabbitting on Thursday, March 05, 2015 - 01:23 pm:

The reason no one wants to do one main is the chance of doing a good job won't happen.

A new ground center line on the crank will not match the one in the babbitt, even if the crank is done right.

It takes just as much labor to do one main, as it does the other two, and you still have a cobble job.

The gears will never match, as the center lines will be different.

There is no way to center a crank in the block indicating off of worn bearings, front, or rear.

If who ever uses a fixed setting on their Align bore, to set the center distance, it surely will never align with all 3 bearings.

If the babbitt is original, that makes it worse yet.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Thursday, March 05, 2015 - 01:31 pm:

It is not quite as easy as just pouring a center bearing and replacing the crankshaft.

First thing is to thoroughly inspect the block for cracks especially in the area of the center main bearing. This should be done by wet magniflux which a good machine shop is equipped to do.

Next unless you are replacing the crankshaft with a new one, you will need to also magniflux the crankshaft, and check for straightness. Then the bearings need to be turned with the correct radius at the ends of the journels.

Next the bearings are poured in the block and the connecting rods and machined to fit the size of the crankshaft. The bearings in the block must be line bored to be in perfect alignment with each other and also with the camshaft so that the timing gears will fit correctly.

I highly recommend Antique Bearing Service in Escondido Ca to do the work. If not them, you need to find someone who has experience with Model T engine bearings to get a good running car.

I also recommend that you check the cylinders for roundness and taper and if they need work rebore and replace the pistons at this time before working on the bearings. It would also be a good time to grind and or replace the valves. The boring and grinding should be done before the bearing work. It is better to do all the work on the block at the same time and in the right order to avoid doing some things a second time.

Anyway, I know this will cost you a bit more than you might have hoped for, but if you do it right the first time, it will save you more in future repairs and disappointments. Your car will sound good and run good for a long time.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank van Ekeren (Australia) on Thursday, March 05, 2015 - 03:49 pm:

If you can find someone close by who has a Gene French line borer and knows how to use it, it can be done.


Top of pagePrevious messageNext messageBottom of page Link to this message  By bob middleton on Friday, March 06, 2015 - 12:19 am:

Sorry gents was a long day
Think i will pass on it unless i can get it cheap doesent sound like a simple fix, and thats what i thought


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