The Stovebolt Site Forums The Shop Area Engine Shop Manually rotating 1960 261 engine for leak test

Hi all,

New to the forum but could not find a thread related to this, so I apologize if I just could get the right search terms to find it.

I have purchased a1950 3100 truck with the 261 in it from a previous restoration, got a great deal on it but its not running (has sat for a year or so unused apparently). Near Zero compression on #5 & 6 so assuming its a blown head gasket but wanting to do the cylinder leak test to verify the issue before pulling the head.

The harmonic balancer has a teardrop feature on it that seems like it might is suppose to be used for manually turning the engine, but unsure about this. It also has what seems to be two unthreaded holes where I assume some sort of tool fit in order to turn the engine manually, but have so far been unable to find anything on the internet about this. (picture attached, I think).

The center hole is where the hand crank fits. You can find them every so often on the big auction site.

That balancer has been pretty badly abused by someone- - - -probably driven into place with a heavy hammer. It also appears that it's an older small diameter balancer that used to have hand crank lugs, that have been ground off. The two threaded holes are 3/8-16 thread, and they are used to bolt on a crowfoot style puller. You can chase those threads with a tap, as they're usually full of rust and grime, and screw a couple of short bolts in, then use a pry bar to turn the engine. I have also made a turning fixture by welding a big nut to a short piece of flat bar, and bolting it to the balancer with those holes. Later model balancers have a squared-off center hole that will accept a 3/4" drive ratchet for engine turning.
Jerry

Lube the valve guides and confirm the valves are not stuck before turning over, soft hammer or 2 x 4 on rocker to confirm.

Ed

Thanks for feedback. So I thought those 2 holes should be threaded, but didn't look like they were, so knowing they are suppose to be helps. Thanks for the tip, I'll chase them and then get a couple of appropriate bolts and give it try.

Also thanks for the idea of lubing the value guides before starting, although since I've already run the compression test its probably late to worry about it too much. But probably would be a good idea to go ahead and pull the value cover and do it, to make sure the values are moving and will be necessary to adjust the values anyway.

Quick feedback... like the site so far, thanks Ed & Jerry.

Be very careful not to use too much effort on the intake rockers @ TDC compression, they hit the piston very quickly.

Just aksing here but how did you do the compression test?

If you want to pressure test all the cylinders without turning the engine, turn the crankshaft about 30 degrees past TDC on the #1 cylinder, lock the crankshaft with a couple of pairs of vise grips on the flywheel where it meets the bell housing, and loosen all the rocker arm adjusters far enough to close the valves.
Jerry

So in case I didn't mention it, the engine is already in a 1950 Chevy 3100.

Pulled the valve cover and seems well oiled, probably from turning it over doing the compression testing. BTW, I did the compression testing using a standard tester from Harbor Freight, and cranking the engine with all the plugs out and cold (since it will not currently start). Moved cylinder by cylinder and averaged 120 PSI on 1-4, and near 0 PSI on 5 & 6 when dry; slight increase in PSI when oiled/wet, but 5 & 6 still near 0. My guess is blown head gasket, but trying to run the leak test to confirm before pulling the head... which lead me down the current path of discussion.

Thanks for the feedback. I did find what seems the perfect tool for manually turning the engine "on-vehicle", a Crankcase Rotation Adapter from Preform. Will try it in the next couple of days and come back with how well it worked (or not).

JMSvintage Don't go off the deep end with your tap and run into your timing cover back there.

A stuck or tight valve will cause very low, or no compression because the valve isn't seating. Always do a valve adjustment and check for stuck valves before doing a compression test. I like to pull all the spark plugs and block the carburetor wide open before testing compression- - - -it minimizes the load on the starter and assures that the cranking speed is the same for all the cylinders.
Jerry

JSMVintage That one looks far gone,you know the originals would send the crank out when it started so it didn't get caught. Have made cranks by heat bending cold-rolled that was big enough you couldn't bend it by hand. If your around the oil field where it's deep enough to have bigger sucker rod 7/8 could use that. once it's bent then put sleeve handle that is captured works good is safe and comfortable.

Hi All,

So I finally found a solution for a manual engine crankshaft rotator (for maintenance, etc) and thought I'd get back to the forum and post what I found. My issue to recap was I had an engine in a 1950 truck already but the harmonic balancer input "slot" was damaged, so could not turn the engine manually the "usual" way. Someone suggested screwing 2 bolts in the 3/8 -16 in the balancer and using a pry bar or similar to turn the engine. Knowing me, that would have resulted in a trip to a Urgent Care Clinic, so I looked for (and found) a better solution. The solution I found was a Preform Crankshaft Rotation Adapter (66782) that has a 1" nut on the front for turning, available from numerous online stores for around $25. Making a paper template I found using 2 holes had close to the right separation and would have worked fine I think; however I did a little Dremel tool shaving to make a perfect fit.

The solution worked great. The adapter was skinny enough that I had little problem getting a breaker bar ratchet from Harbor Freight (ICON with flex head) on it. Turning was easy at this point.

Thanks for all the comments and suggestions, which ultimately lead down this path and the ability to run the tests I needed to. Seems I have a head that needs some machine work... but that's another thread :-).

Joe

Forgot the pictures, but no obvious way to attach any. The "attachment manager" seems to not let me select .jpg files.

If someone educate me on how to do this I'll upload, but searching on the Proform part will show you anyway.