250 Crank Work

[Stan Lipert]

Just sharing some photos of a recent crank refurbish. 1965 Mk3 250.
I machine the oil journal a fresh face, disassemble to clean and inspect, found all of the rollers and bearing surfaces good, press together and true.

I faced the oil journal before disassembly, since the crank was true from the factory:


After pressing apart, I welded a slide hammer bar to pull the pin cap. Plenty of sludge. I can then cut off the weld tack, a little sanding, and then reuse the cap:


Rod has little wear, no pitting. Wire wheel to clean:


Pressed together, I use a 1.5 pound brass hammer to true, easiest done is for me to use a straight edge to get the outside faces of the wheels parallel.
Checking was done by spinning the crank in the cased, with an indicator on the oil journal:


Total runout of 0.001" is good for me!
The timing case will get a custom oil feed bush to match the new smaller O.D. of the journal. I go for 0.003" clearance.

Stan

[flanker]

That's clean work Stan! Impressive!,,

[flanker]

My sump was filled with what looked like petrified oil

[Nick]

Thanks for that. Great info, and nice work.

I've trued many cranks using a brass/led hammer and then measuring runout on a crank truing stand, but I didn't know you could also check the trueness with the crank installed in the cases.
Have you confirmed that you get the same readings with the crank in the cases as with the crank on a truing stand?

[Stan Lipert]

Nick, I would probably use a truing stand if I had one, to save time. Since the final destination of the crank is bolted into the cases, isn't this more accurate?

[Rick]

When I saw your photo of the bungee cords through the connecting rod I remembered having seen that done maybe 40 years ago, but I forgot about it probably 39 years ago- glad you sparked my memory.
I think you'd get more accurate truing using a stand rather than the crankcases- looseness in the bearings, dowel pins,etc, would accumulate to make the readings better than they really were. If you could borrow a stand you could take the crankshaft out of the cases and see if you get the same reading on the stand- I doubt if they'd be the same. The best stands I've seen are made for balancing grinding wheels for surface grinders- with your shop and experience making a copy wouldn't take long. Plus, with a stand, you wouldn't need to take the crankshaft out of the cases to make adjustments.
I have some bench centers, but I don't trust that the crankshaft ends haven't been buggered up, so I've never used them.
Rick

[Stan Lipert]

Okay, next time I get a chance, I'll compare with a truing stand.
I don't trust bench centers either- that beveled hole at the end of each crank is where a hammer may have been used for disassembly.

This got me thinking about crank flex and vibration. I know that the bearings are loose when cold, and the cases expand when hot, and the bearings get looser when the cases get hotter, and the crank bends and flexes at each rotation. It would be interesting to see how much the oil journal wobbles around.
I can tell with authority, that every engine that I've tuned on a dyno, the engine will make the most power when it is HOT. The looser the better?
I think so.....

[double diamond]

Tony Foale describes a very simple and effective crank truing stand at: http://www.tonyfoale.com/AermacchiEngin ... ntTool.pdf
I agree with Tony that this tool is better than supporting the crank between centers or supporting the left and right journals in a stand.

Matt

[Rick]

Stan,
I didn't want to drive the bearings all the way onto the crankshaft, and couldn't find my test indicator, but these photos show a simple rig that will probably be better than using the cases:

true 1.jpg

true 2.jpg

You probably have v blocks and parallels in the shop.
And anything Tony Foale does is well thought out.
Rick

[Stan Lipert]

Double,
Tony's jig/fixture is cool, but this was in response to him not knowing where his crank was bent. I probably have trued more cranks than Tony, having worked as a mechanic for years. I have not had a problem crank yet that I could not true, including bent rod big end pins.

Rick, I have a surface plate, machinist v-blocks and machinist parallels, but I think the cases are more accurate. Is it a problem not knowing where to press/wedge/hit?

Stan