Comet Smoking After Rebore Is the Bore Glazed ?

[Matty]

Hi All
Have now had a +20 rebore with a new VOC piston and for the first few miles there was no smoke. However now after around 4X 20 mile runs last week at 40/50mph, it smokes badly (the weather is frosty, salt on roads, and I am 79 so I only did short runs) !!!
Tried disconnecting the oil return and taking it via a pipe to the oil tank, to miss out the valve gear for a few minutes and it still blows out smoke,
So conclude problem is with the bore/piston not valve guides, which in any case looked very good and have only done 3000miles or so.
Compression is very good, but I think the bore must have glazed up (I took great care that the piston circlips were in correctly so do not think this is the problem)
Obviously I do not want to pull it apart again if possible, but if it is glazed, are there any magic cures, or should I just drive it harder for while to try to bed the rings in.
If it is glazed and I have to have the bore honed to de-glaze it, how should I run the bike in to avoid this problem happening again ?
Have posted this again as a separate item from a previous post, because Glazing may be of general interest. I think I had the same problem about 10 years ago after a rebore but can not remember the details.
Matty

 

[Howard]

Suspect you're right about glazing, and can't offer any answers for you, but would like to say you're an inspiration, and hope I'm still riding in Winter when I reach 79 - I'm just a 66 year old kid.

H

 

[BigEd]

Assuming that any holes to feed the cylinder are at the right height it could be that you have been a bit too gentle. Current thinking seems to be that a bit of load is required to force the rings onto the cylinder to get a break in.
As to age, if Matty and Howard are still riding at 79 and 66 they are 79 and 66 years young not old.

 

[Howard]

Assuming that any holes to feed the cylinder are at the right height it could be that you have been a bit too gentle. Current thinking seems to be that a bit of load is required to force the rings onto the cylinder to get a break in.
As to age, if Matty and Howard are still riding at 79 and 66 they are 79 and 66 years young not old.

Ah yes VOC = Very Old Children.

I don't know if it's relevant but I've read that new synthetic oils are not good for running in older design of engines.

H

 

[Matty]

Thanks for the prompt replies.

I am sure the oil hole is bored at an angle to come out well below the scraper ring and checked this very carefully some years ago when I had a new liner and a rebore to standard. However I blanked the feed to the oil hole long before this latest +20 rebore so this can not be the cause of the blue smoke.

The oil I am using is Morris Golden Film 20/50 which it claims is specially formulated for classic cars and bikes. I do not know if is fairly "straight" oil or semi-synthetic - it does not say on the can. However most of my friends in the VMCC and VOC seem to use it without any problems.

Will try "blasting " the old bike for a good distance on a big road this afternoon in a straight line at a constant fairly high speed (60-70) to see if this helps and if not get the barrel honed again.

Not too worried in the short term because it will be OK for club runs, but hope to have it fixed before my annual ride (250 miles) up to Liverpool for the Manx GP (now Classic TT)

Matty

 

[mercurycrest]

Ah yes VOC = Very Old Children.

I don't know if it's relevant but I've read that new synthetic oils are not good for running in older design of engines.

H

I agree, I stuck both my A anc C Comets using Mobil 1. 15-50 M/C oil....... and knocked the babbit out of my F4 Moggy's rods! Mobil's ads about how great it's "oil" is are pure crap! The good part is, I switched to Brad Penn oil and the Moggy got rods with insert bearings.

 

[Matty]

The weather turned rather nasty so I have not tried to bed the rings in yet at higher speed.

Thanks - but don't quite understand Mercurycrest reply, think there may be some language problem.
Assume "stuck" means engines damaged and the Moggy is a Morgan with a JAP or Matchless air cooled engine.

Was the Mobil Oil fully synthetic ?- I do not believe the oil I use is even semi synthetic.

Matty

 

[Nulli Secundus]

Morgans can also have 4 cylinder Ford engines.

 

[Matty]

Morgans can have V8 engines now or a big American V twin !! But the 1923 2 speed one that I drove on quite a long a journey for a friend in the early 1950s had a side valve Matchless engine, no brakes, the throttle on the steering wheel and was very exciting when I was 17.

 

[Albervin]

Matty, make sure you have a working breather. Squirt a bit of RedEx or similar upper cylinder lubricant into the carb or even down the plug hole. This will cause initial smoking but may deglaze the bore and/or rings. I am glad to see you are a "hands on" rider and thinking through the problem at hand. Good luck.