Author Topic: Plunger camshaft problem  (Read 637 times)

Online Greybeard

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Plunger camshaft problem
« on: 09.06. 2018 17:37 »
As the topic 'GB is not OK' ran for over 20 pages I've decided to summarise the posts for anyone who needs to know about the problem I had.

I have a 1955 A10 Plunger, with the semi-unit engine, (gearbox bolted to crankcase). The engine developed a light rattle.

I discovered that the sump strainer had caught pieces of yellow metal, (See pic 1 Left), a Little End bush had broken up, (See pic 1 Right). I also discovered that the camshaft and followers were badly worn and needed replacing, (See pic 2).

I already had a new camshaft. It was a 67-356, (designed for the Star Twin, Road Rocket & Shooting Star). (See pic 3 left) Item 67-334 is correct for this machine but I could not find one at that time. I asked the experts on this forum if the alternative camshaft was suitable for my engine. The consensus was that the 356 camshaft had a slightly higher cam lift but was commonly fitted to the standard engine and the only possible problem was that the larger cams may touch the sides of the case in the cam trough, (See pic 3 right). This might mean a few minutes working with a Dremel or similar to ease the case.

On reassembly the engine would not turn over a full revolution!

Eventually, a suggestion was made by forum member Chaterlea25 that the problem might be valve collets coming up against valve guides.  I found that the collets I had were wrong for the valves. The ones I had were item 65-1624, (See pic 4 left) and were designed for the Road Rocket & Super Rocket. They have an annular raised ring inside that engages with a rounded groove in the valve stem, (See pic 4 left). They also project too far below the valve collar. They were, in fact, causing the problem, (See Pic 5). The correct collets for the valves I have are item 29-410, (See pic 4 right). They are plain inside and grip the tapered waist of the valve stem. They barely project below the collar.

My bike had been running fine with the wrong valve & collet combination for six years but putting a higher lift camshaft in caused the bottom of the incorrect collets to come into contact with the valve guides.

I rushed off to my local BSA parts seller and bought a set of the correct collets and a set of new valve springs. When the top end was reassembled the engine spun over freely! Phew, what a relief.     

Offline duTch

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Re: Re: Plunger camshaft problem
« Reply #1 on: 09.06. 2018 17:42 »
Just curious if the offending collets have been ground shorter, can yo do a quick measure of them ? 

Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

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Re: Re: Plunger camshaft problem
« Reply #2 on: 09.06. 2018 18:00 »
Just curious if the offending collets have been ground shorter, can yo do a quick measure of them ? 
I doubt if they have been modded though.

Offline muskrat

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Re: Plunger camshaft problem
« Reply #3 on: 09.06. 2018 21:46 »
G'day GB. Well done  *yeah*.
I should have twigged a lot earlier, from the mods I did putting SR valves into the A7SS.
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

Online berger

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Re: Plunger camshaft problem
« Reply #4 on: 09.06. 2018 22:21 »
the SR collets ive got for my ss head are 11.11 mm long as apposed to 4mm for standard A7 ss valves and ive had to do a lot of collar reducing to accomadate the 357 cam and stop spring bind, but didn't have to touch the cases {cam trough} 4 blooming days of dry build to get it right,and that's when I found the cam followers can pick up 2 cam lobes if its not in situe

Online chaterlea25

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Re: Plunger camshaft problem
« Reply #5 on: 09.06. 2018 22:36 »
Hi Berger,
Is the collet taper angle the same on the SR and A7, A10 ??? I thought it was different
The best way I know of to accomplish the SR valves into the A7 head is to get the "Gold star" valve spring conversion
These uses short collets with the semicircular  valve groove

John

1961 Super Rocket
1963 RGS (ongoing)

Offline muskrat

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Re: Plunger camshaft problem
« Reply #6 on: 09.06. 2018 23:30 »
G'day John.
Yes your right the angle is slightly different. I had to machine the A7SS collars to get the right fit and use the A7SS springs.  *pull hair out* the things we do  *ex*
Cheers
'51 A7 plunger, '57 A7SS now A10CR,  '83 CB1100F, 88 FXST .
Australia
Muskys Plunger A7

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Re: Plunger camshaft problem
« Reply #7 on: 09.06. 2018 23:49 »
ive got SR valves collars and collets for the inlets, the bottom collars had to be machined flat to get spring clearance......the exhausts are shooting star with the bottom collars machined down on the underside and the valve stems turned out towards the top of the valves to lift the collars to get spring clearance {NIGHTMARE} just to add the inlet springs are SR the exhausts shooting star

Offline Peter in Aus

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Re: Plunger camshaft problem
« Reply #8 on: 10.06. 2018 00:52 »
Thanks GB for doing that, I'm sure that will make life easier for members in the future.  *good3*
Peter

Busselton West Australia
49 A7 longstroke
58 A10  SA

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Re: Plunger camshaft problem
« Reply #9 on: 10.06. 2018 08:19 »
Thanks GB for doing that, I'm sure that will make life easier for members in the future.  *good3*
Peter

I could have further simplified the story as, 'Make sure you have the right collets you numpty!'

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Re: Re: Plunger camshaft problem
« Reply #10 on: 11.06. 2018 09:51 »
Just curious if the offending collets have been ground shorter, can yo do a quick measure of them ?
7/16"

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Re: Plunger camshaft problem
« Reply #11 on: 11.06. 2018 10:24 »
The valves I changed six years ago were the correct type, so the wrong collets were either put in by me in 1973, (I probably decoked the engine when I first got it, but I don't recall if I changed any parts), or they may predate my ownership of the bike.