Author Topic: Plunger gearbox mount misalignment  (Read 473 times)

Offline mark

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Plunger gearbox mount misalignment
« on: 13.10. 2022 01:07 »
Trial fitting the engine gearbox unit into the frame on the Super Flash project. All mounts except the top gearbox will line up as the pics show but there is about 1/4” misalignment between the frame end gearbox lugs. Both bottom gearbox bolts are installed as well. The bike was in bits when I got it. Also engine and frame match factory records. My initial thought is that the frame lug may have to be modified to suit. Any thoughts appreciated
Mark
1955 Road Rocket
1953 Super Flash



71 Norton Commando Roadster 750


Australia

Offline mark

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Re: Plunger gearbox mount misalignment
« Reply #1 on: 13.10. 2022 02:24 »
I checked the horizontal distance between the rear frame lug and front engine mount lugs to the best of my ability and compared it to what I calculated it to be from a schematic of the super flash frame that I found on the forum. The diagram indicates 15” and mine measured around 15 1/4”. So this may be the issue. If I just bolt up the 3 gearbox bolts it lifts up the front of the engine so that neither of the engine mounts line up.
1955 Road Rocket
1953 Super Flash



71 Norton Commando Roadster 750


Australia

Offline Jules

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Re: Plunger gearbox mount misalignment
« Reply #2 on: 14.10. 2022 11:26 »
hhmmm, so how do you expect Steve Martin to fix that Mark?? bend the rear tube in 1/4" or??? I dont know much about the plunger frame, are there options, slot the mounts etc?? cheers

Online RDfella

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Re: Plunger gearbox mount misalignment
« Reply #3 on: 14.10. 2022 17:36 »
How does the primary chain fit? If it's overly slack, maybe someone has machined the crankcase or gearbox faces. Maybe a shim there would assist.
'49 B31, '49 M21, '53 DOT, '58 Flash, '62 Flash special, '00 Firestorm, Weslake sprint bike.

Online Greybeard

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Re: Plunger gearbox mount misalignment
« Reply #4 on: 14.10. 2022 17:43 »
How does the primary chain fit? If it's overly slack, maybe someone has machined the crankcase or gearbox faces. Maybe a shim there would assist.
Is that likely? The gearbox output shaft would be off centre to the seal in the case?
Greybeard (Neil)
1955 Golden Flash, sprung frame
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Re: Plunger gearbox mount misalignment
« Reply #5 on: 14.10. 2022 19:47 »
G'day Mark.
Looks like the PO has hit a gutter quite hard and pushed the lower mount up. I think that would be the only mount that could be worked on to rectify it.
Cheers
'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
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Offline mark

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Re: Plunger gearbox mount misalignment
« Reply #6 on: 15.10. 2022 03:14 »
Gearbox shaft seems to line up correctly so I believe that it’s the frame that is out. Will take it to Steve Martin who has the frame dimensions for the Super Flash and have him check it out for me, then work out the best solution. Will keep you posted
Mark
1955 Road Rocket
1953 Super Flash



71 Norton Commando Roadster 750


Australia

Offline Swarfcut

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Re: Plunger gearbox mount misalignment
« Reply #7 on: 15.10. 2022 08:03 »
 If the gearbox bottom mounts and cross stud all line up fine, the lower frame members are OK. Could be the frame was made that way and there is enough flex in it to line up that top mount. Cross support between plunger forgings and a car jack should do it. But this is not how it should be, frames under tension are a bad thing. When assembling frames and engines it is always easier to have everything loose so parts can move  and settle get every fixing in place and then tighten.

 If the frame fella's check is OK, the easiest fix is to add material to that gearbox top lug and redrill to match.  But before anything is done  it may be worth checking that the mudguard, air box and oiltank fit. If not this is a pointer towards something further amiss with the frame.

 I'm sure somewhere there is reference to a shim type gasket sometimes fitted between the gearbox mounting face and the crankcase. I reckon this was a factory dodge to keep the mainshaft concentric with the seal on examples of over enthusiastic machining. So RD has a point, and another gearbox shell for comparison would certainly help to sort this conundrum.

 Swarfy.

Offline mark

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Re: Plunger gearbox mount misalignment
« Reply #8 on: 20.10. 2022 02:39 »
Took it to the frame man today, needs to be put in the jig and straightened, he feels that it is the front mounts that are out, probably by being hit and there may be other damage under the powder coat. So will get it stripped and he will look at it in January.
1955 Road Rocket
1953 Super Flash



71 Norton Commando Roadster 750


Australia

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Re: Plunger gearbox mount misalignment
« Reply #9 on: 20.10. 2022 10:10 »
G'day Mark.
January  *eek*
Back in the early 90's I got Laurie Alderton http://aldertonmotorcyclerepairs.com.au/about-us/#tab-68da5371-2e64-2 to do my Cafe (57 A7SS) frame. It came from South America with sidecar mounts on the wrong side! Two weeks from drop off to pick up.
Cheers
'51 A7 plunger, '57 A7SS racer now a A10CR, '78 XT500, '83 CB1100F, 88 HD FXST, 2000 CBR929RR ex Honda Australia Superbike .
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Muskys Plunger A7

Offline mark

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Re: Plunger gearbox mount misalignment
« Reply #10 on: 20.10. 2022 22:38 »
They look good however I’m in Melbourne. I seems to be very common at the moment that businesses have a lot of work on with quite a backlog. I guess that I will have to be patient. Good news is that I stripped the front section of the frame and there are no obvious repairs so fingers crossed it will straighten up ok
1955 Road Rocket
1953 Super Flash



71 Norton Commando Roadster 750


Australia

Offline Russ

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Re: Plunger gearbox mount misalignment
« Reply #11 on: 23.10. 2022 06:07 »
Mark I had my Plunger Frame checked (just to be sure), no issues just a tweak or two, by Mick Maloney in Inverloch. PH 0409962595.
It was a few years ago now and cost $100.
1951 A10 Plunger.
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Offline Beeza

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Re: Plunger gearbox mount misalignment
« Reply #12 on: 23.10. 2022 06:27 »
You can also ask Bike Magic in Moorabbin, can’t remember his name but he did a frame for me, might be worth a call.
Cheers
62 A10 BVSR, 62 A10 RGS, 53 SFS