Pits in drum

[John Illinois]

I have decided to use kevlar linings. Is this band too pitted to use. I was originally going to polish it.

John

[Steve Jelf]

Get a better drum. Taking off enough material to remove pits that deep is a bad idea.

[Joe Bell]

You have a really nice gear on that drum, I would replace the drum with Dave Noltings and it would be perfect balanced and new, you have it down this far what is another couple hundred dollars. If my own engine is down that far I would replace at least the reverse and low speed drum, they get all the abuse!

[John Illinois]

Thank Steve and Joe. That is what I thought. I have 2 of Dave’s drums and they are very nice plus he is great to deal with.

John

[Adam]

Measure it first! I’ve seen plenty of “junk” drums that are oversize enough that they clean up nice at close to standard. Particularly ones out of early to mid twenties engines. I have a suspicion that during periods of high production demand that drums may have been turned and ground to a larger spec to reduce machining time.

Turning the drum .040” undersize (which is a .020” cut) results in the band ears being 1/8” closer together than they would be with a stock drum. The correct stock drum diameter is 7.500”. I would not use a drum machined to less than 7.460” which is a .020” reduction in designed wall thickness, plus there are a whole lot of other considerations and judgment calls. The drum casting must be very concentric, can’t be “too thin” (there are apparently some design and/or mould variations), the drum should be verified to be free of cracks, shouldn’t require any further reduction of material (such as balancing), etc. The “payback” on machining a drum undersize is thrift at the potential expense of longevity.

I highly recommend a new ductile iron drum from Nolting Machine. They are made from billet, not a casting and are machined all over which makes them very close to balanced when installed and generally require very little additional balancing if you are doing a full balance/blueprint job.

[Norman Kling]

That drum might be ok for wood band linings. It would just cause a slight groove in the wood without much of a problem. However, any fabric band such as Kevlar, cotton, or Skandinavian would be a potential to snag the material and cause fibers to get stuck in the oil lines or other parts of the engine or transmission. If you don't want to spend for new drums, use wood lining.
Norm

[StanHowe]

Every damn time I try to post something and don't save a copy I get a screen that says "the site is down," it dumps my post and wastes my time!! I've about had it!!!!!!!

It has now dumped it three times in a row!!!

So this is what I wrote. Or close to it.

Like all of this it depends on what you are doing. If you are doing a cost is not object gonna drive it a thousand miles a month want it perfect -- yeah I'd buy a new one.

If I had a better drum I'd put it in. But what I probably would actually do is set up my tool post grinder on my lathe, put a fine stone on and true it, set up a drip so I was wet grinding and grind about 10-15 off of it and see how it looks; probably use it. A few small pits wont hurt it.

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[RGould1910]

I used a brake drum with a larger pit than yours. I was concerned that the band material might catch and fray so I used a dremel tool to smooth out the edges of the pit. Worked fine.

[John kuehn]

That’s a good idea about smoothing out the holes or pits. You can do the same thing in Babbitt rods too. Use to do that in IR Rand large air compressors at the air base where I worked.