Ironhead crankshaft width ironhead

[JB in NC]

I know this is an old thread, but I would like to add my observations based on experience.

Assembling a flywheel assembly with a new aftermarket crankpin will usually result in the rod side float on the crankpin to be larger than the spec. That is not really a problem within limits. It is not unusual to see rod float at .030 - .035, and that is OK. Why is this? Because the replacement crankpins are usually made wider than the original. That is to make up for worn tapers in used flywheels. What you don't want is so much end float that the bearing assembly can move so much that a rod race catches the edges of adjacent rollers. And remember that the bearing assembly has more end float than the rods, by design. This issue is so pervasive for both XLs and big twins that I have made checking rings to compare crankpins taper-to-taper.

It was mentioned that the width of the flywheel assembly will not affect its fit in the case. For the '76 and earlier cases nothing could be further from the truth. A wide flywheel assembly will cause the right flywheel to rub the case. (The left flywheel position is set by the Timkens and does not change.) The cures for this are to find a narrower crankpin, to press the flywheels together (which I have done but do not recommend), to face the right side flywheel for clearance, or to trim the sprocket shaft shoulder to move the whole assembly to the left.

I hope these remarks will shed some light on a subject that is lightly covered in the service manuals.

Jim

[kitabel]

The Timken controls flywheel lateral position in the cases, they don't "float" like roller bearing engine

[Ferrous Head]

So you can imagine my happiness when an accomplished machinist helped me by "cleaning up" the case faces for me. The reason they went there was for a C/S boss fix.

To be fair this can be done with most other engines with no drama's.

[needspeed]

Originally Posted by JB in NC

..It was mentioned that the width of the flywheel assembly will not affect its fit in the case. For the '76 and earlier cases nothing could be further from the truth. A wide flywheel assembly will cause the right flywheel to rub the case.

Hi Jim.
I assume that your comment about fitting a wide crank in crankcases is a reference to my post where I told the OP that he shouldn't have a problem.

If my memory serves, I once determined that the cranks run about .060 from the right side case. Based on the end play given by the OP his crank appears to be about .025-.030 wider than normal.

I know that some have had issues with the wheel rubbing the case. But with those dimensions I felt in this case there should be no problem.

Other factors can affect the crank position such as the dimensions of the sprocket shaft flange, shaft taper and wheel taper size and how far the shaft is drawn into the wheel.

Thank you for your informative post. I just wanted to explain why I gave the OP the advice that I did.

Obviously these machined assemblies not all created equal.

[JB in NC]

Originally Posted by needspeed

Hi Jim.
I assume that your comment about fitting a wide crank in crankcases is a reference to my post where I told the OP that he shouldn't have a problem.

If my memory serves, I once determined that the cranks run about .060 from the right side case. Based on the end play given by the OP his crank appears to be about .025-.030 wider than normal.

I know that some have had issues with the wheel rubbing the case. But with those dimensions I felt in this case there should be no problem.

Other factors can affect the crank position such as the dimensions of the sprocket shaft flange, shaft taper and wheel taper size and how far the shaft is drawn into the wheel.

Thank you for your informative post. I just wanted to explain why I gave the OP the advice that I did.

Obviously these machined assemblies not all created equal.

It's very much a case by case situation. Pun completely intended! I see you have had enough experience to have run into this issue before. I have found that a flywheel assembly with a wide crankpin can cause a rub with as little as .03 added width. I don't know where the problem area is in the case. I just know, flywheels too wide, bolt the case together, flywheels rub.

Jim