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Hegel
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Posted: Fri Oct 3rd, 2008 12:58 pm |
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Got a couple of questions regarding 750 Commando barrels, if anyone couple give me a bit of adivice?
The bike already has +30 pistons in it, can't seem to find any info on what the max rebore size is? Also is it possible to get the barrels re-sleeved?
I've also been reading quite a bit about the pros and cons of getting them bead blasted, tho some say the problem is that some residual glass get left on the surface + making sure none gets into the oil ways, etc. They are pretty rusty on the outside, want to get them back to a decent finish. Thoughts?
<edit> Oh I nearly forgot...Is it necessary to replace the rings once the barrels have been taken off? I saw in the manual that they should be replaced. If they're not letting any oil past them..Is it necessary really?
Thanks,
HLast edited on Fri Oct 3rd, 2008 01:00 pm by Hegel
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Frankfurt-Beesa
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Posted: Fri Oct 3rd, 2008 01:27 pm |
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I think Norton go to +.060 oversize bores, resleaving? I don't know, piston rings only really need changing when they are worn out or the cylinders are rebored, to make sure they fit, check the end gap when fitted square in the cylinder, the manual should show how to do it right and what the end gap should be.
Bead Blasting is an option, but if they are only rusty then caustic soda would do the job too without risk of blocking oil ways or residual blasting medium getting into the engine.
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Hegel
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Posted: Fri Oct 3rd, 2008 01:57 pm |
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Hi Fb 
Thanks...Ah, my bad...I forgot they were cast iron. It does beg the question...Has anyone ever made alloy replacemnts with sleeves? Or have they?
Sorry I'm so much in the dark still about this bikes engine 
So how does the caustic process go then?
Oh...Incidentally I found some commando engine rebuild videos...I had to join the NOC to get them tho.
Cheers,
H
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L.A.B.
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Posted: Fri Oct 3rd, 2008 11:30 pm |
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750 pistons are available up to +60 thou oversize from Norton parts suppliers such as:
Norvil: http://www.norvilmotorcycle.co.uk/
RGM Motors: http://www.rgmmotors.co.uk/
Mick Hemmings: http://www.mickhemmings.com/
Also try the suppliers above for alloy barrels, or Steve Maney: http://www.stevemaney.com/
Sleeves are available to take the barrels back to standard bore.
Have you actually fitted the rings into the bores and measured the ring gaps to see if they are worn or not?
In my opinion, a new set of rings (and a bore hone) are cheap insurance against future problems, and using the old rings (if they do show any signs of wear) is just unnecessary penny-pinching.
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Hegel
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Posted: Mon Oct 6th, 2008 10:27 am |
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Hi L.A.B.
Thanks for your reply
I joined the NOC last week, saw they did some rebuild videos (Mick Hemmings), so I bought them. I have to say...
They're absolutely brilliant! Certainly took away the niggles about certain aspects of the rebuild.
No, I've not stuck a ring in yet to check the gap. The fellow who owned/rebuilt it, said it'd done 10k miles since...tho it seems to run ok (Apart from the dodgy clutch), I'm really tempted to pull it right down, since by the state of the oil I dread to think whats lurking in the sludge trap Anyway, as you say I think it'd be the thing to do, get the bores honed and some new rings.
Oh..Btw...What does everyone use to polish con rods?
Thanks again for the links,
H
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L.A.B.
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Posted: Mon Oct 6th, 2008 10:52 pm |
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Hegel wrote: Oh..Btw...What does everyone use to polish con rods?
I use ordinary metal polish such as Solvol Autosol.
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Hooli
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Posted: Mon Oct 6th, 2008 10:54 pm |
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L.A.B. wrote: Hegel wrote: Oh..Btw...What does everyone use to polish con rods?
I use ordinary metal polish such as Solvol Autosol.
is this actually worth doing on a stock engine that isnt trashed to the rev-limit very often? i know it reduces stress risers so makes them stronger i just dont know how important it is.
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L.A.B.
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Posted: Mon Oct 6th, 2008 11:48 pm |
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Hooli wrote: i know it reduces stress risers
I consider it necessary to remove all nicks and scratches, at least from the front and rear faces of the rods, although I'm not sure it actually makes the rods stronger, it's just supposed to stop cracks developing, and prevent the rod failure that can happen as a result with alloy rods. Last edited on Mon Oct 6th, 2008 11:50 pm by L.A.B.
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Hooli
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Posted: Tue Oct 7th, 2008 12:00 am |
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L.A.B. wrote: Hooli wrote: i know it reduces stress risers
I consider it necessary to remove all nicks and scratches, at least from the front and rear faces of the rods, although I'm not sure it actually makes the rods stronger, it's just supposed to stop cracks developing, and prevent the rod failure that can happen as a result with alloy rods. fair enough, sounds like something else on the plans for the winter then.
at least inside the engine they'll stay clean & shiney right? none of that nasty oil that drips down the outside over shiney bits 
EDIT: i take it, its just polish smooth rather than mirror finish?
Last edited on Tue Oct 7th, 2008 12:01 am by Hooli
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L.A.B.
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Posted: Tue Oct 7th, 2008 10:41 pm |
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Hooli wrote: EDIT: i take it, its just polish smooth rather than mirror finish?
That's probably OK, but I do like to get a shiny finish on them.
Apparently once polished, the rods should be oiled immediately and wrapped to keep the rod surfaces from oxidising and not just left on a bench or shelf, or hung somewhere where they can be admired - until such time they are refitted?
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Hooli
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Posted: Tue Oct 7th, 2008 11:27 pm |
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cheers chaps & sorry for hijacking your thread Hegel
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