Crank Shaft Rod Pin Replacement

[Go Go Diablo]

Hi all,

The Hirth motors use a crankshaft with a press fit pin holding the two halves together. Not sure what a JLO crankshaft is like. Of course, between the halves is the piston rod, rod bearing and two brass thrust washers. To replace a rod or rod bearing, the crankshaft halves need to be pressed apart. That was the easy part. However, the rod pins are round without any means of a timing mark or spline to put them back together straight.

So, now the hard part.

Does anyone have experience on pressing crank shaft halves back together and the proper technique to do so. My biggest concern would be how to determine if the two halves are back together square and straight with each other. Is this done by putting the assembly between two centers and checking runout, or by installing bearings on the crankshaft and then rolling the assembly on the bearings and checking for runout, or is there another means of alignment?

Looking forward to some responses.

Bruce

[fap67]

I don't have any experiance doing this, but this is what I've seen. In the late 1980's, I was at a Polaris dealer and they were straightening a 3 cylinder crankshaft. It had already been pressed back together with new bearings. From what I remember, they were spinning it with the bearings resting in v-blocks. To straighten it, they had a large pair of pliers with curved jaws to hold the crank and a lead hammer. I would find a service manual for a twin or triple cylinder or search the internet of the procedure. As far as I know. on the JLO single cylinders, you had to buy a complete crank assembly with the rod on it. There wasn't any individual parts available, such as connecting rods, therefore the repair manuals don't show the pressing and straightening procedure. Let us know what you find out, I have a JLO 252 crank that is out of time. How it got this way, I don't know. I wonder if it could be put back in time and would it stay that way.

[blimkijw]

Hi Bruce,

So I figured out how to used tese so called forum thingys now!! piece of cake, maybe dad shoulda let me on the computer more as a kid rather than work in the shop I could be a little more informatve.

So pressing apart a single cylinder crank is a piece of cake with the right equipiment of course. I have not pressed apart a diablo crank, but I have done numerious motocross cranks and my 444 crank in the past to give you a few helpful hints,


-Then with a set of feeler guages, measure the side clearance between the weights and the rod. dont quote me exactly but .015" per side rings a bell, (Check you manual though)
-Then what you can do is scribe a line on the counter wieghts to get you in the ball park when pressing things back togther
-Press apart the crank, inspect and replace what is required.
(24hrs before place lower rod pin in freezer so that it will shrink that little (.0005) and make sure that the start of the pressed pin has an adequate chamfer on it so that it will press headache free, and take pin out on momentariy before to assemble)
-Prior to pressing apart the crank , take the time to deburr the cranks counter weights and con-rod from any rough casting, (Thats my call) Then wash thouroughly when apart
-So then press pin into one of the weights, then assemble the rod, bearings and side shims if it has them then press the second half together trying to get both scribed lines as close togther with maintaining your con-rod side clearance or your lubrication.
With the crank now looking like a crank I opt to use a collet chuck in a lathe to clamp onto the crank on a tru surface. Then with an indicatior on the opposing end of the crank hit the counter weight with a dead blow hammer or lead hammer to rotate the counter weight until it is indicated tru to the other end of the crank, Usually 0.000-.002" is what I aim for, closer to zero the better but them machine didnt rev hight enuff to notice . Umm after that check ther side clearance of the rod bearings again then white glove check it for dirt, oiler up and assemble. If you do not have a lathe You can use v-blocks on a flat surface (wifes granitecounter top works good LOL !! or granite surface plate) Its jst a little hard not working with the crank secured and more prone to dirt.

I think I didnt forget anything, You tube it it maybe, but the singles arent to bad especially if you have access to a hydraulic press and a lathe, butmatching v-blocks work too

[Go Go Diablo]

Those are good suggestions Justin. I hope to get back at this crank in the next few weeks and hope to make some progress.

Bruce