Rebore dilemma

I would re line your existing barrels, but as you say expensive. If your quick there are two 99 barrels on ebay £35 bid at the moment, which could be a cheaper option. From experience your biggest problem is finding someone to re bore to size, with bore ovality to within 0.0002", use the correct grit for your rings when honing, leave the desired crosshatch and finally plateau hone the bore. I've had partial success in the past but I am still looking for a machine shop to do the job right first time. HT Howard in Reading are possibly worth a call, not in your area but may be worth the traveling in the long term.

Just had a closer look on ebay and the two barrels seem only marginally better than scrap.

Previously mike_chizlett wrote:

Hi All

My 1956 domi 99 cylinders are currently on plus 40 and piston ring gap is in excess of recommended tolerances.

As I see it this gives me three options,

1. Fit new liners and take back to standard bore (very expensive)

2. Rebore out to plus 60 (expensive)

3. Fit oversized rings ground down to working tolerances (cheap)

There seems to be some debate as to whether boring out to plus 60 is a viable option as thinning the wall of the liners can result in cracking leading to possible untold damage.

Option 3 would be a quick fix but is only putting off the inevitable.

Your views would be most welcome.

Also can anybody recommend an engineering shop that could perform options 1 and 2 near the Tunbridge Wells, Kent area

Many thanks

Mike

In my experience, if you rebore to +060, there is a likelihood of the top spigots cracking eventually. If they do, you can just machine them off (or use less subtle methods). The thinning of the cylinder walls should only be significant if you throw a rod which will undoubtedly destroy the barrels. But then of course, so it would at +040 or even sleeved. If the bores are not particularly worn, why not re-ring? Check the ring gaps at top and bottom of the stroke and if they are pretty much the same (define please!), new rings should do the job.

Hi Mike, A lot depends on how you rate "expensive". As a "boring old fart", who paid less for a Dominator in the 50's than a pair of silencers cost today, the price of all spares seems outrageous! RGM offer new liners at £32 each, of course you have to add the cost of new pistons & rings. There is an engineering firm, in Rye, E. Sussex, run by John Brewster (who used to work for Weslake, and who is a Norton enthusiast). He specialises in making, and machining parts for obsolete engines. Sorry, I don't have his number at hand, but, if you are interested I could probably get it in a few days ( I am in Spain at present). John.

Hi again Mike, I have just found John Brewster's details, on the web.JHB Engineering, Unit 4A Jempson's Trading Estate, Winchelsea Road, Rye, E. Sussex, TN31 7EL. Tel. 01797 226 775. You may well find it worth talking to him. John.

Previously mike_chizlett wrote:

Hi All

My 1956 domi 99 cylinders are currently on plus 40 and piston ring gap is in excess of recommended tolerances.

As I see it this gives me three options,

1. Fit new liners and take back to standard bore (very expensive)

2. Rebore out to plus 60 (expensive)

3. Fit oversized rings ground down to working tolerances (cheap)

There seems to be some debate as to whether boring out to plus 60 is a viable option as thinning the wall of the liners can result in cracking leading to possible untold damage.

Option 3 would be a quick fix but is only putting off the inevitable.

Your views would be most welcome.

Also can anybody recommend an engineering shop that could perform options 1 and 2 near the Tunbridge Wells, Kent area

Many thanks

Mike

Hello Firstly what are your three measurements that you did up and down the bore to deuce a rebore was necessary I can tell you that owners think they need a rebore and they do not as they have not measured the bore in the three prescribed places in the length of the bore, and if need any over size ring then please contact Dale Middlehust the Heavy twin expert you need the right rings And DO NOT buy GPM Piston ring , As they are not the right circumference and will not fit . yours anna j