TheSamba.com :: View topic

Thu Jun 21, 2018 1:34 am

When trying to fit new main Kolbenschmidt bearings into my engine, I note that the circular bearings are tight and need a small tap with a rubber mallet to seat into the saddles.

However the split number 2 bearing needs a decent whack to get it seated.
I replaced the bearings like for like for the old ones. The workshop advised I did not need to line bore and provided the replacement bearings.

When removing the old bearings, they come out with a bit of a tug but understandably the new ones are much tighter. So it appears that the saddles are OK. I did measure these with a bore gauge and satisfied myself that they were within spec, but I can't now find the readings.

I attempted to measure the "ovality" of the new split bearing. Not sure if this method introduces too much error or not. I clamped the two bearing halves together with a soft faced clamp. The length measured from the split to split was 65.7 mm i.e. 0.2mm wider than the nominal saddle size (65.5mm - 1st case cut) whereas the diameter of the non-split side was 65.5mm. Measuring the original bearings in the same manner, I got 65.5 which is spot on.

Is this normal i.e. the width at the split is wider and should pull in when the bearing is pushed into the saddle. Or is it possible I have out of specification bearings.

Thu Jun 21, 2018 2:49 am

The problem is that there is a discrepancy in the quality of todays bearings. Make sure that the bearings are aligned with the pins, and install the crank only. Torque the case, and see if there is any binding on the crank.

Fri Jun 22, 2018 4:34 pm

OK. I've learned something more.

Bearing spread apparently is within the tolerance of 0.2mm. That is, the diameter one way is larger than the saddle diameter.

Bearing spread is there to help hold the bearing in place during assembly and assists in keeping it in place during operation.

Still it appears MUCH tighter than any bearing I have installed before. I will attempt to install the crankshaft, torque up and see if it spins ok.

Fri Jun 22, 2018 9:41 pm

When you bolted the case halves together, what did the bores measure?

And without the bearings installed?

Mon Jun 25, 2018 3:09 am

I tried to do this with expanding internal telescopic gauges but cannot get an accurate enough reading use those and my external micrometers.

I'm going to try and borrow a proper internal micrometer to get an idea, but given my information I've posted on bearing spread being up to 0.2mm, Im more comfortable now than I was before.

Thanks for all the inputs.

Mon Jun 25, 2018 5:44 pm

Technique matters here as well. Ask the guy you borrow the gauge from about that.

Max