Mk 8 Hewalnd - Bobbin (for throwout bearing) clearance?

[Robert J. Alder]

I had the brass bushing in a clutch bobbin seize up on the input shaft. Weird. Did so after just one weekend. The good news, after removing tranny I was able to easily pull the bobbin off the input shaft with help of a bearing puller and was also able to clean up the input shaft. Just a bit of brass deposited on the input shaft which cleaned up nicely. Also able to press the brass bushing out of the steel bobbin.


Input shaft before cleaning it up.


Bobbin and bushing and you can see the gaulding (sp?) in about the first 3/4" of the bushing. (In case you're wondering it's an installation using a Lotus ~3" adapter instead of the usual ~2" adapter. Thus a 1" longer input shaft and longer bobbin required. Also, it's a Tilton clutch.)

Anyway, it was a brand new input shaft and a bobbin that I had from somewhere. Maybe I'd honed the brass bushing in the bobbin for a "nice" fit over the input shaft that didn't have enough clearance and it tried to seize up after being used a bit.

Does anyone know what would be a proper clearance (i.d. of brass bushing vs. o.d. of input shaft)? Scotty, you out there? I can re-press the brass bushing into the bobbin and then re-hone the bushing i.d. to get more clearance. In the past I've seen bobbins where the brass bushing was pretty beat to hell and they still worked OK. So too much doesn't seem to be a huge issue. But to little clearance?????

Any suggested a proper clearance to shoot for.?

[john f]

Bearing should be oilite. Never hone, ream to size. Too much better than too little. Standard bronze fitting is .001" to.0015" per 1" dia. You could go .003 - .005 per inch with no problems. Make sure NO bronze left on shaft. Just my $0.02.

john f

[Robert J. Alder]

Thanks, John. Don't know if the bushing was Oilite or not. Any way to really tell?

[john f]

Thanks, John. Don't know if the bushing was Oilite or not. Any way to really tell?

Heat it with a propane torch. It will sweat oil.

john f

[Jerry B.]

RJA

try 2868T192 from McMaster-Carr.
Your bobbin might be another i.d. bobbin dimension from what I use...they have other dimensions with same composition . That material wears well for the application.
.005-.008" seems to be good.

JB

[Robert J. Alder]

You guys are so smart. Thanks for all the input. Turns out it was a "homemade" bobbin and it was just a bronze bushing, not an oilite bushing, which was a tad tight to begin with. Bad combo..

Scotty at Taylor came to the rescue with some nice oilit bushings with proper id for the input shaft that had oversized (o.d.) because the silly homemade bobbin bore was too big for a standard 1" OD bushing.

Thanks. All is well and a cheap fix.