Mystery Primary Cover

Classic short-frame models

Mystery Primary Cover

Postby wz507 » Fri Jan 27, 2017 12:54 pm

A friend showed me this cover and it is unfamiliar to both of us. Does not appear to be a one-piece part, as the clutch hub bulge appears to be swaged/brazed in. Also one mounting hole on the flange is not drilled. Any thoughts would be welcomed. Apologies for the poor pictures. Thank you.

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Re: Mystery Primary Cover

Postby mikeslemmon » Fri Jan 27, 2017 1:15 pm

early ch I think befor 1963
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Re: Mystery Primary Cover

Postby sportsterpaul » Fri Jan 27, 2017 1:44 pm

Agreed, two-piece steel stamped primary 1958-1963 in black, 1964-1969 in chrome. I believe all the factory production steel covers were two-piece for strength, but maybe some XR or KR race bikes used a one-piece unit. The aftermarket primaries are one-piece stamping. I tried to sum up the production primary covers here:
http://www.open-sport.org/BOM/Engine/Pr ... ary_cover/
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Re: Mystery Primary Cover

Postby Maxcapacity » Fri Jan 27, 2017 1:58 pm

The undrilled mounting hole is for the XLR case. XLRs have one extra (10 total) Primary mounting screws. All the early tin covers I've seen have the provision but the only ones that get drilled are for XLR installation.
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Re: Mystery Primary Cover

Postby thefrenchowl » Fri Jan 27, 2017 3:00 pm

It's worse than that lads!!!

It started purely as a KR and XLR tin cover, despite the fact it was also used at some stage on CHs...

The clue is the slightly wider than required location for the 10th screw.

KR had a 30 teeth max sprocket and the 10th screw boss in the KR case was moved slightly back on the XLR case to cope with the XLR 34 teeth sprocket. Hence they went from KR only tin cover with normal 10th hole dimple to this one with an elongated space that could be drilled either for KR and XLR.

Obviously, not drilled for CH that only have 9 screws.

The twin skin was more to do with falling on the left hand side on flat track corners, lasted a touch longer before the clutch went out of service.

Patrick
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Re: Mystery Primary Cover

Postby JerrryR » Fri Jan 27, 2017 3:18 pm

Is the spot up front where the main shaft would protrude flat or does it protrude slightly. If it is flat I think it would be for an early CH like in 58 and rare?
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Re: Mystery Primary Cover

Postby thefrenchowl » Fri Jan 27, 2017 5:32 pm

All from factory shots, ie period..

52 KR tin cover, cooling scoop, no access to chain, round stamping for 10th screw, single skin all flat, no fins:

Image

56 KRTT tin cover, flat, single skin, round stamping for 10th screw, new rib all the way encompassing chain access hole:

Image

1958 XLR/XLC/XLCH, same XLR bike used for all the factory shots, start of elongated stamp to use on both KR and XLR:

Image

1960 XLR tin cover, raised bit at mainshaft nut location:

Image

1968 Rayborn's Daytona KRTT: 9 screws only tin cover, in fact late 60's CH tin cover:

Image

1969 iron XR prototype tin cover, 10 locations but only 9 screws, that's because they reverted to 57 XL sand cores for iron XR and XLR cases, these have only 9 bosses in case.

Image

1970 as sold iron XR tin cover, back to late CH tin cover

Image

Patrick
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Re: Mystery Primary Cover

Postby EKHKHK56 » Fri Jan 27, 2017 5:43 pm

Very nice Patrick. Thank You for sharing this. You've got us covered :D
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Re: Mystery Primary Cover

Postby thefrenchowl » Fri Jan 27, 2017 6:17 pm

Have you noticed the missing little screw on the last 2 XR covers!!!!!
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Re: Mystery Primary Cover

Postby mikeslemmon » Fri Jan 27, 2017 7:45 pm

all the xlr and kr cases I've seen have the lugs for 10 screws but the covers are . interchangeable except for some kr's [early I fhink].
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