Author Topic: GB is not OK!  (Read 5420 times)

Online Greybeard

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Re: GB is not OK!
« Reply #45 on: 25.05. 2018 14:31 »
Gudgeon pins are OK.
Big end shells are -10 undersize. Pistons are +20 oversize.

There are a couple of scores along the timing side bore. This seems to explain why that exhaust would smoke after I revved the engine and why there is a lot of carbon in the combustion chamber. I'd like to try and avoid a rebore; how much will honing remove? The scores are not severe but can be felt with a thumbnail.

It certainly looks like the old camshaft and followers have overheated. Either I tightened the tappets too tight, or the hardening failed, or a combination of both :/

Looking at the camshafts I see that the new one I have is a 67-356; the knackered one and the presumably original one I took out when I restored the engine are both 67-334's. What's correct for my engine?

Offline RogerSB

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Re: GB is not OK!
« Reply #46 on: 25.05. 2018 16:33 »
Hi GB, I hope I'm not the bearer of more bad news for you.
I've checked on the parts lists I have and A7/A10 plunger and s/arm 1954-57 is 67-334. That same number is also listed for A7/A10 s/arm 1958-59.
67-0356 is listed for A Group 1960 - 62.

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Re: GB is not OK!
« Reply #47 on: 25.05. 2018 16:51 »
Hi GB, I hope I'm not the bearer of more bad news for you.
I've checked on the parts lists I have and A7/A10 plunger and s/arm 1954-57 is 67-334. That same number is also listed for A7/A10 s/arm 1958-59.
67-0356 is listed for A Group 1960 - 62.
Thanks, Roger, I've now found my own parts list and I see that the 67-356 is ok for the year of my machine but is for the Star Twin and Shooting Star. What difference would this make to my low comp engine?

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Re: GB is not OK!
« Reply #48 on: 25.05. 2018 17:01 »
Not a lot. The 356 will be absolutely fine.
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Offline RogerSB

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Re: GB is not OK!
« Reply #49 on: 25.05. 2018 17:11 »
Thanks, Roger, I've now found my own parts list and I see that the 67-356 is ok for the year of my machine but is for the Star Twin and Shooting Star. What difference would this make to my low comp engine?

Yes, 67-356 also for the 1954-57 Star Twin and Shooting Star, however I'm not that technical savvy to be able to advise but I'm sure someone here will be able to.

Edit: There you go *smile*.

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Offline RogerSB

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Re: GB is not OK!
« Reply #50 on: 25.05. 2018 17:33 »
Not a lot. The 356 will be absolutely fine.

Are the lobes slightly higher, causing the valves to open wider?
Or are the lobes a slightly different profile to affect the timing of the opening and closing of the valves?
Or a combination of both?

Edit: If they lift the tappets and pushrods higher would valve spring strength and valve clearance be something to consider?

1960 Golden Flash

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Re: GB is not OK!
« Reply #51 on: 25.05. 2018 17:53 »
Not a lot. The 356 will be absolutely fine.

Are the lobes slightly higher, causing the valves to open wider?
Or are the lobes a slightly different profile to affect the timing of the opening and closing of the valves?
Or a combination of both?

Edit: If they lift the tappets and pushrods higher would valve spring strength and valve clearance be something to consider?

I await more input from the Southern Hemisphere...

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Re: GB is not OK!
« Reply #52 on: 25.05. 2018 20:49 »
G'day GB.
A 356 will be fine in your motor and give a fair increase in performance (a couple extra ponies). No problem with springs and clearances. Looks like the new one has been nitrided  *wink2*.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Re: GB is not OK!
« Reply #53 on: 25.05. 2018 20:53 »
Thanks, Musky. How about the tramlines in one bore? Can I just get it honed?

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Re: GB is not OK!
« Reply #54 on: 25.05. 2018 21:11 »
Yes I don't think it's bad enough to warrant a rebore. Try to keep the piston/bore clearance to 5 thou", they will run with more but sound sloppy. New set of rings and away you go.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Offline chaterlea25

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Re: GB is not OK!
« Reply #55 on: 25.05. 2018 21:12 »
Hi GB,
The lines in the bores are the result of shrapnel from the cam and followers
If otherwise unworn I would opt for a hone and a set of quality rings, you might find scores on the rings????
The 356 cam will be an improvement  and should run quieter later figures for valve clearances apply
Next question is the quality of replacement followers  *????*
I have not had problems with SRM's stellite faced ones, I have fitted them to all the A engines I have rebuilt

Good oil return is no indication of how well  *doh*the pressure side is doing  *doh*

John
1961 Super Rocket
1963 RGS (ongoing)

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Re: GB is not OK!
« Reply #56 on: 25.05. 2018 22:02 »
Thanks guys!

Offline KiwiGF

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Re: GB is not OK!
« Reply #57 on: 25.05. 2018 22:52 »

It certainly looks like the old camshaft and followers have overheated. Either I tightened the tappets too tight, or the hardening failed, or a combination of both :/

Looking at the camshafts I see that the new one I have is a 67-356; the knackered one and the presumably original one I took out when I restored the engine are both 67-334's. What's correct for my engine?

I’ve a (srm) 356 cam in my ‘56 and it’s a straight swap with the 334, it’s generally accepted there is no downside to the upgrade to a 356 from a 334. The 356 was fitted to late GFs and early rockets. The later 357 cam as fitted to rockets can hit the crankcase of a GF due to its higher lift, but even this is easily fixed with a grinder  *work*

I don’t think you easily could buy a new 334 anyway. I’ve a box of used ones I doubt anyone would want!

My guess is your old 334 cam was ground to return it to shape and was not re-hardened afterwards, and the grinding went through the hardening layer, leading to the excessive wear you can see on the cam, it’s possible the followers had the same fault.

There is risk with re grinding A10 cams and followers that afterwards the tappets are not able to touch the cam base circle, there is not much extra movement in the followers before they hit the “stop” in the barrel.

It’s got to be worth a try hone and new rings (at most) isn’t it? I fitted new pistons on a used rehoned bore and 005 plus a bit clearance and it runs great, no smoke or rattles 7500 Miles later.
New Zealand

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Online duTch

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Re: GB is not OK!
« Reply #58 on: 26.05. 2018 00:05 »

 I can't add anything that I can think of that hasn't been said, except o say that I'm running a re-ground 67-357 in my early BA10 and it goes fine and doesn't clash in the oil-bath, although some of the points raised above have niggled in my mind as they came to my attention after I'd rebuilt it ie;

 
Quote
There is risk with re grinding A10 cams and followers that afterwards the tappets are not able to touch the cam base circle, there is not much extra movement in the followers before they hit the “stop” in the barrel.

 One thing I'll ask GB is if you can measure the length of your pushrods, if it's no trouble ?

 Hoping it all goes well- don't stress though, (your) Summer hasn't even started yet so you'll still have plenty of daylight to do it.. *smile*
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
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Re: GB is not OK!
« Reply #59 on: 26.05. 2018 08:50 »
dutch, I'll get back to you later on that. They are £SRM push-rods.