Crankshaft index arrow

Brumbach · Post by **Brumbach** » Mon May 28, 2018 5:59 am

What is the significance of the arrow index on the crankshaft rear flange? I can't seem to find reference to it in the manuals. I have read on other sites that when it is positioned at 12 O'clock it "can" indicate TDC but not necessarily. I'll bet it serves to orient the installation of the flywheel since the flywheel rear scribes TDC and 5 degree BTDC are used in conjunction with the cover plate in setting everything for timing. I know how to determine TDC and set timing. Just curious about the arrow. Thanks in advance.

Post by **wesk** » Mon May 28, 2018 10:34 am

Post a photo of your arrow!

Brumbach · Post by **Brumbach** » Mon May 28, 2018 12:07 pm

The crank is loaded. I'll give it a try.

Post by **wesk** » Mon May 28, 2018 12:51 pm

It always makes questions much easier to answer or research when they are accompanied by a photo.

Is the arrow painted or engraved?

I ask because I just looked at my cranks and they do not have any arrows on the front face of the rear flange.

Perhaps your arrow was added by a prior owner to help with indexing the crank to the flywheel for balance purposes?

Brumbach · Post by **Brumbach** » Mon May 28, 2018 1:03 pm

Take a look. http://www.willysmjeeps.com/v2/modules. ... _album.php

That link above is for the smaller copy of your photo.

This is the link for the larger copy of your photo: http://willysmjeeps.com/v2/modules/gall ... G_3426.jpg

If you put this before this link it will appear as a photo here in your post.

1st you left click on the " Img " icon above here and the " will appear at the end of your photo link.

It only took me 5 seconds to do everything I told you in the above paragraph resulting in your photo appearing here.

Brumbach · Post by **Brumbach** » Mon May 28, 2018 1:10 pm

If you can zoom in you can see the arrow clearly. I don't know if that's possible at posted on photo gallery. I'm tech dumb when it comes to this stuff.

Post by **wesk** » Mon May 28, 2018 10:01 pm

That arrow is clearly an index mark for the flywheel positioning. I noticed you edited your posts above because I could swear you said the arrow was on the other side of the flange originally.

Again, my M38 crank does not have the arrow. Since it is etched on yours so lightly it would not be visible thru any heavy corrosion or pitting.

I have always been in the habit of make indexing marks on cranks and flywheels on old engines for two reasons.

1: these are often dynamically balanced as a set.

2: early engines had the timing marks on the flywheel and these flywheels can be installed 2 ways each 180 degrees apart. When you pick the wrong flywheel index you end up having to use #4 TDC instead of #1 TDC for timing.

Brumbach · Post by **Brumbach** » Tue May 29, 2018 3:17 am

I did edit as the statement was in error. I realized it when I went to take the photo. You must've read as quickly as I'd posted it. Sorry for the confusion. Thanks for the response.

Post by **wesk** » Tue May 29, 2018 9:38 am

It will keep things more understandable in these long threads when you edit an earlier post if you leave the error and add the correction so both can be seen and the full text of each reply afterwards is better understood.