Engine blown - Cylinder spigot fractured

[muskrat]

Bugga, forgot to add scans.

[MG]

Looks like the A65 crankcases are a bit wider and offer some more space for larger bores/spigots???
Other than that, seems not too far off. Is the distance between cylinder centres the same? Hard to tell from the head gasket pics.

[Triton Thrasher]

Maybe not too relevant, but new Pre-unit T*****h barrels are less of a problem. I suppose it's because you can make any 650 barrel, 1950-1974 out of the same casting.

Anyway, casting and machining A10 barrels must be hardly rocket surgery.  Can't the Owners' Club commission some?

[Mark Parker]

Maybe you could trace the bores from the A65 H/gasket onto paper and sit the A10 flange gasket in place and see how much room there is for the thickness of the spigots. I've had an A10 crank in an A65 so bore centres are not a problem.

[muskrat]

 I remember one of my first race motors (A7) that I through bolted, I built up the cases mouth where I added the studs by about 2mm and just got the spigots past. Shed closed for the night but will do a little digging tomorrow.
 Got me thinking of a 75mm bore A10 is close enough to a 750 and with a A65 head 
Cheers

[Mark Parker]

These are 76mm, would give 762cc if it's possible to fit, 75mm gives 742cc, around that size would be optimal I would think. A70 pistons have the better pin height.
http://www.shopevengineering.com/productdetail.htm?productId=-293797&catalogId=-2087&fpg=1
It could be set with less compression 10.5 - 1 might be a bit high. 9 -1  would be kinder on the old cranks. Even getting pistons made specially wouldn't be difficult. These type of forged piston are especially good value.

[MG]

Pistons are no problem, I had these made for my CSR, cost me 750 Euros landed, for a set of 4 (minimum order), incl. rings and pins. Imho not bad value for forged, custom-made equipment, quality is excellent, and with some material removed on the inside also good weight-wise, and you can get them made to own specs.

[chilblayth]

the original bsa cylinders were machined from the casting   , i had a pair of cylinders  resleeved by grampian motors in 1977 ?   approx ,  unfortunately i took too long coming up with the cash and he sold them on me  so i cant comment on if its a sound solution !   but i remember looking at them and there was a small crack running down the barrel spigot on one side  which i didnt like the look of , personally i think there isnt enough metal on the lower spigots  coupled with the fact these original barrels are 50 yrs old  , when the liner gets hot it expands , i think at a faster rate than the original metal, !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
recipe for disaster 

[KiwiGF]

Well I've just had some thick flange lined barrels honed to suit some new STD bore JP pistons, they have ended up just 001 over the clearance JP recommend

The liners and old pistons had some scoring from a seizure but the liners had not moved, it never occured to me liners were a bad idea. I thought this was a standard solution once 060 over was reached and maybe even the liners could be bored -020 to prolong barrel life even further.

Fingers crossed the lined barrels I have last OK then!

[bsa- bill]

The liners I had fitted were old Hepolite stock.
The shop that fitted them were quite happy to do so and you have to wonder would Hepolite have produced them if there was any doubt.
IIRC Tthe liners have to be bored after they're fitted to bring them to size and in line

[chaterlea25]

Hi All,
If the cylinder is correctly sized and the liners fitted properly there should be no problems!!
Where the liner runs through the spigot it should be just a push fit  (no interference fit)
As the liner is always hotter than the cylinder block it will stay tight
As mentioned in another thread modern adhesives are magic

Going back a few posts, Mark Parker mentions oversize A65 exhaust valves
Does anyone (Mark) know where I could get these from?

Regards
John O R

[1660bob]

My barrels are sleeved back to standard, lucky me, or am I ....- the first thing I saw on stripping the motor was a nice big crack in the spigot.It seems to me that A10 barrels are short of "meat" to begin with, borne out by the mod to later thicker flanges.Boring and sleeving an already marginal design is i think, pushing ones luck at least and borne out of desperation. There is almost bound to be a slight difference in expansion in the two materials surely, however small, it can`t help matters.I couldn`t enjoy riding the bike knowing that lumps of brittle, cracked cast iron were poised ready to fall into the whirling  crank assembly....... we need new barrels, either cast as original, or alloy with liners. How aboutit Santa?  

[BSA_54A10]

The barrels are plain grey cast iron
So when you get them sleeved you specify grey cast iron sleeves.
Cast iron usually expands at the same rate as cast iron so there should be no problems caused by different expansion rates
Cast iron sleeves are a little more expensive than steel sleeves.
If you want to be real choosy then ask for spun cast, fine grained cast iron sleeves as these have a better grains structure than standard cope & drag castings.
As for spigots cracking, more likely causes are resonant frequency vibrations, sloppy assembly work, impact from the conrod.
The spigot end of the barrels does very little work

[Mark Parker]

   The valves I use in my A65 are cut down Jaguar 6 valves, they are cut shorter to A65 length and new collet grooves cut, rather than welding hardface on the tappet end I just fit hardened lash caps. The Jaguar exhaust valves are too big so I have the heads turned down to 39mm, it still leaves seat area. The inlets are ok at 44.5mm but usually need cutaways in the pistons enlarged. The ones I use are black nitrided, and can run quite close in a k/lined guide. Sometimes the cast in inlet seat is not well lined up with the valve and needs a new seat fitted so the inlet isn't trying to seat on aluminium, most heads are ok. If you run the big valves in a 650 or 750 with large carbs 38mm for eg, it can run sweetly over a wide rpm range so long as the header dia stays std, if you up header dia you can up power but you may not get it till 4,500 -5,000 though it depends on the pipes and how you port the head. The latest head on my 880 motor has "D' shaped inlet ports, the floor of the oversize port is filled and flat as it turns under the guide. All it does is fill a deadish flow area, I don't think it flows less, yet certainly goes better with the increased gas speed bringing power in earlier.
   An alloy block in my opinion is much better with Nicasil than a liner.

[chaterlea25]

Hi All,
Mark,
Thanks for the info on the A65 valves etc,
I have a long term project with a 1925 Chater Lea that has an ohv Blackburne engine, It had been bodged beyond all recognition inside the engine 
Anyway it turns out that A65 valves are almost identical in length and head size to the Blackburne
The A65 stems are smaller so I made new guides to suit,
However the standard A65 exhaust valve sits very near the inside of the valve seat, which is why I am looking for one a couple of mm bigger!
I have a couple of "Goldie" valves which I can turn down and the radius tool for the groove,
As you say hardened caps will sort the valve tips
I was looking for an easy way out 

On the gas speed subject, I used to have a Morini 3 1/2,  Those things really flew with brilliant handling 
Apparently the designer had a major "thing" for gas speeds
Heron heads, that had what looked like "small" ports
The exhausts pipes were double skinned as well

Cheers
John O R

[Duncan R]

Hi All,

Just split the cases - large lumps of spigot and assorted shrapnel all in the bottom end.

Initial inspection seems promising, main bearing bush undamaged, rods still straight, crank journals appear untouched, camshaft also OK. I think it was an instant break so engine locked and there was no time for any of the debris to get round the engine.

Obviously it will need a thorough cleaning and everything blown out and inspected properly, so hopefully once some cylinders  and new pistons are found It can go back together.

Happy New Year

Duncan