Damage to barrels

[gavinoz]

Hi all, went to remove the powdercoat from these thick flange barrels, and saw this damage to cutaway. Do you think this this damage will affect the piston, skirt, cooling, movement etc, if I get them rebored and smooth the fracture? Thanks, from Gavinoz

 http://i1059.photobucket.com/albums/t432/gavindally/003.jpg

[duTch]

I'll stick my neck out- not the most ideal situation, however..

I just measured up some barrels & pistons Flat top 7.25? & 8.? (same to crown)
 Top of bore to bottom of spigot                                           =            149 mm.
 Flat-top piston crown to bottom of skirt                               =    66 mm
 Stroke(to top of piston@ bottom of stroke from top of bore)  =   84 mm - 
          add 66mm from top of piston to bottom of piston         =            150mm.
Therefore bottom of piston skirt @ bottom of stroke is ~same~ as bottom of barrel spigot(in my case).
   The breakaway appears to be at the front of the barrel, where it just catches the change of direction at the start of the upstroke(intake)for a few degrees so depending on the thrust on the piston at that point (maybe at the front-bottom or compensated? , as the pin is slightly biased to the bottom /// mm >crown to pin 25- pin19- pin to skirt22<)-maybe not good but not so bad??.
       That's how I see it, without casting opinion, but food for thought.. Believe it or not I do have (other)things to do!
 Cheers duTch
 
 

[iansoady]

I had similar damage to a Norton Commando block when I lost all the oil & broke a conrod. Being very impecunious at the time I just smoothed the edges off where the piston would contact and it was fine for several thousand miles (till somebody nicked it).

I'd say you would probably get away with it.

[RichardL]

Mine is slightly damaged, but in width, not height. So far, about 3000 miles without a problem (that I know of). In your case, Gavin, I would want to be sure the rings don't enter the damage zone. I don't think they will, but measure nonetheless. Also, await a bit more advice from our seasoned engine specialists before blindly accepting mine.   

Ian, yours is probably still running fine, just somewhere else. (Sorry for the joke and your loss).

Richard L.

[chaterlea25]

Hi All,
Following oon from Dutch's measurements I went and had a looksee at the Barrels awaiting assembly for my RGS project engine
If the pistons skirts come level with the bottom of the spigots the bottom of oil rings is about level with the base of the flange, so it should be well away from the broken area
It would be very important to smoothen any rough areas  and radius off any sharp corners
Looking at the other cutaways they seem sharp cornered??? I would undercut the corners with a small smooth round file
I would think that you will get away with the damage provided you follow the above
I am attaching a pic of the modified cutaways on my barrels to Dutch's conrod thread
Regards
John

[baz]

unless your going racing they should be fine just check carefully for any cracks and radius and chamfer the edges as statated above,also two stroke piston rings survive running across huge ports in some barrels without problems ..........baz

[Butch (cb)]

Though of course two stroke rings are pegged so as to ensure that they don't turn in service, until an end coincides with the port. Oops.

[bsa-bill]

Though of course two stroke rings are pegged so as to ensure that they don't turn in service, until an end coincides with the port. Oops.

You have me puzzled on this one Cyclobutch, are they not pegged so that the ends don't turn and come anywhere near a port

go on tell me I've missed the point

[Sparky]

How far over are you going to have to bore the cylinders?  Depending on that, the skirt can get somewhat thin.  If you want to spend a few more bucks for the peace of mind, you could consider having it reserved.

[Sparky]

Darn autocorrecting spell checker... reSLEEVED, not reserved,

[fido]

Though of course two stroke rings are pegged so as to ensure that they don't turn in service, until an end coincides with the port. Oops.

You have me puzzled on this one Cyclobutch, are they not pegged so that the ends don't turn and come anywhere near a port

go on tell me I've missed the point

I think his point was that our A series rings are not pegged so if a ring is going to sweep a missing bit of barrel it could end up with the ring end lined up with the missing section.

[bsa-bill]

Cheers Fido and apologies cyclobutch, I must of missed a mail in that subject - oh the joys of advancing years!

Now for another try to put my foot in it
On the subject of reboring, would the edge of the missing bit cause any concern to the boring machine or would they just chamfer the edge

[iansoady]

I don't think they would automatically chamfer it - it would just be treated the same as the existing slot.

[duTch]

Sorry Fido, I beg to differ, and'm sticking with b-Bill on this, but Cyclobutch did say " Though of course two stroke rings are pegged so as to ensure that they don't turn in service, until an end coincides with the port. Oops.'

    In Gav's case (and thanks to John for finishing off the maths for me- I knew I was going somewhere with it, but attention span didn't cope), it seems the rings are not coming so far down as to encroach on the break, so shouldn't be a prob.

Cheers duTch

[gavinoz]

Thanks all, I am listening with interest.
To give you the whole picture, my bikes, lovingly shipped from UK 25 years ago, have remained at back of shed untouched. I cannot even recall what parts are there. I am very very slowly starting to work on them, and as budget is limited, I am working on the swinging arm bike, which is in pieces. I am building my dream A10, which is purely my quirky vision of the perfect A10, and has features from many models. I love the looks of the fully enclosed chaincase, (no matter how fiddly), deep valenced mudguards, and headlight cowl. I love the Ariel style hubs. I love the Type 6 carby. I dont like chrome, so the tank will be my own take on a nice BSA tank.
I havent even got a Haynes manual (left it in UK). So I look at this forum to refresh old knowlege and for new info. I am starting with the head and barrels. The forum is great. e.g. I have 2 alloy heads (I just like the look of the alloy head: unlike Muskrat, I am not a speed freak, and high performance isn't critical) One I have removed the white powdercoat from. Gasket remover did work, thanks bsa-bill) the other is exactly as described by 1660 bob in 2010, so now I have learnt about bronze thread inserts (which had worried me with my alloy heads). I still have to remove the siezed sparkplugs, about which there is another thread. I really appreciate the wealth of experience of forum members, and their willingness to share knowlege in the friendliest of fashions. I will get going on my barrels next, using the advise from you all.
Thanks again, Gavin