Gonna try something dumb

[Coyotemutt]

I discovered that my center main parting line surfaces had worn against each other a little bit. Enough to show light through the seam with a bearing in place. Without the bearing it all looks fine. I decided to reduce the crush fit on the center main a smidge using a fine flat file. That allowed the parting line to close, but created drag on the crankshaft.

Well, everything else in this case checks out so I decided I'm modifying the cheapest part. The bearing is a Silverline solid aluminum alloy bearing (meaning no Babbitt or other layers). I've very carefully sanded away material from the inner diameter using 600 grit, oil, and the crank as a guide to keep things round. Sand a bit, test fit, repeat. For the final step I scraped the bearing with a flat knife to make sure any embedded abrasive would be removed from the aluminum surface.

My thinking is that the crank doesn't know if its sitting in a modified bearing or not. As long as the hole is round and has the correct clearance all should be right with the world. My next step is to plastigauge it just to see if I put any taper in it. From the outside it all spins exactly as it should, you'd never know I did anything so ridiculous.

If it doesn't work out I'm probably going to have to stop playing with VWs for a long while. Can't afford or justify a new case at this point. So it's either give this a shot or give up now.

I wont have this fully assembled until mid March.

[slowsixtyduece]

Do you own a dial bore gauge and a few micrometers? If not, get them before you go any further. With the current quality of reproduction bearings and parts, DO NOT skip this step and assume all is well just because there is no more ‘drag’. What happens when the motor warms up and the parts expand due to heat? Not knowing your exact bearing oil clearances is a sure fire way to potentially ruin an engine you have sunk your hard earned money and time into.

Silverlines are unpredictable right out of the box - you never know what kind of clearance you will get, and plastigauge will not show the variations of clearance throughout the circumference of the bearing.

The only way to confidently know your clearance is correct is to use some micrometers and a dial bore gauge to find the difference between crank journal OD and bearing surface ID at various positions throughout the bearing circumference, with the bearings properly torqued in the case.

Additionally, and in the same manner, the only way know if your main bearing bores are out of whack is to find the variations by using the bore gauge, running the anvil around the bore at positions such 12/6 o’clock, 3/9 o’clock, 4/10 o’clock, 1/7 o’clock, as seen in my image below (even though those are bearing oil clearances):



I’m sorry if this sounds like a drag, and I hope it doesn’t cause you to put the project on the shelf...good luck!


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[Coyotemutt]

Thanks for the sound advice and respectful post!

I have more time than money so I'll do everything I can to ensure I have a nice round home with the correct clearances.

Also, I know my center is a little bit out of whack for sure because the parting line surfaces looks almost polished... definitely some fretting.

I'll keep my eyes open for a dial bore gauge though. That would be a handy tool.

[chickensoup]

if you file a split bearing, wouldnt it be less round than it was? my .02

Also, sometimes its ok to have super small gap when the center main is installed and torqued. A friend had the same issue on a type 4. some even said it would be better like that for expansion purposes. personally tho I would buy a new bearing until I find one that fits. VWNOS seels single bearings as well as ebay and ACN.

[Coyotemutt]

My first passes set me up with .001 clearance all around. Not quite enough, but at least it was round.

I took a few more passes and got the clearance I need, but it has more variation in roundness. The spread in any direction came out to .0025 at the tightest and .003 at the loosest. I had to mark the high spots, pull the bearings, clearance those spots, re assemble and then re-check. Alot.

It was fun honestly, but not at all worth the time if you have easier options available.