The Stovebolt Site Forums The Shop Area Engine Shop Timming Marks

I have a 51, 235. My question is about the timing marks. I have flywheel markings of " 111, O(BB), then triangle. TDC is the BB I assume. If I want 2 degrees before or after what do I do? What do the other marks mean? The eng is not running.

Glenn,

There should be a UIC mark also. The I between U and C is TDC or Upper Center. The ball should be 6 degrees before if it is a 51 flywheel.

The triangle is used when checking cam timing.

Thx Dave. I'm rechecking those marks.

Glenn,

I'm a rank amateur, and I'm sure Dave probably knows more about this than I do, but I can tell you this is one of the more confusing things I have run into. Without going into a lot of detail, I had a terrible time getting my truck to start after rebuilding the engine. When I finally used the triangle as the timing mark, it started on the first try.

I do have a later model engine than yours, and that may make make a difference. Allen

I have a a '55 235 in my '40 GMC. Its using a 41-54 flywheel. When I put it in I tried to time the distributor using the BB mark, but it wasn't right. I found that the triangle was the correct mark. I set it there and it runs great.
Steve

ndnchf,

I am just starting a similar swap to yours - I am putting a 1962 261 into my 1942 truck ( with 1940 engine ). I just pulled the flywheel from the old engine, and see that the bolts fastening it to the crank are a bit smaller than the new engines counterpart - will this be a problem?

Also, does the flywheel only bolt to the crank 1 way? If there is a way to index it wrong I usually like to try that way first - or did Chevrolet anticipate this and make the drive dowels on the crankshaft tail end only fit the proper way ( so that these timing marks line up when the #1 cylinder is at TDC )?

The easy way would be for me to try it, but the new engine is on a stand and access to the back of this motor is not available right now.

Thanks,


Stewart

Not only are the bolts smaller on 1940-41 but the center pilot hole is larger.

It would be best to use a 1942-62 flywheel.

The bolts and pins are offset so it will only go on one way.

Stewart,

The 40's flywheel holes are smaller and present a problem. Fortunately for me, the '55 235 I used came with a '41-'54 10-3/4 clutch flywheel. So I used that. As Dave mentioned, using the later flywheel is the way to go. Make sure you get one with the ring gear to match your starter (6 volt or 12 volt). While the 6 flywheel mounting holes look symetrical, they are actually made slightly different so the flywheel can only mount in one position.
I wrote up some lessons learned from the swap here:
http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=2;t=010423#000000

Steve

Now would be a good time to mention that you use the hole above the starter to time it, not the hole on the driver's side.

Steve,

I read your post about your swap and appreciate your details about it.

I will be at the machine shop tomorrow and talk to the man about opening up the mount holes on my old flywheel. The drive goes through the dowels, so I hope he can sneak my 261 crank mount bolts thru - as I don't know how availible 235 or 261 flywheels are in Canada.


Stewart