The perils of linered cylinder barrels or how to loose your head

[PaulMeredith]

The barrel had been bored out to the diameter of the spigot below the flange. Presumably because the spigot was damaged. The failure started on the drive side of the barrel ( the thinnest part ) . The flange broke up and being still bolted on the timing side tilted to the right causing the liner spigot to brake out the side of the drive side crankcase. Once free the barrel and liner was hammered to death against the crankcase mouth.
Paul M

[nevhunter]

I 've seen this happen at least 5 times on rallies over the years and have a collection damaged cylinders off motors of about another 8 or so. This is life threatening stuff. Not only does the engine lock up (you can declutch quickly sometimes) but the head etc has to go somewhere and perhaps jam the front wheel not straight ahead. I had a horn bracket at the front break and the horn stayed swaying on the wires , intermittently locking the steering. I can assure you THAT is dangerous. Sleeving some cylinders turns them into paperweights. Through bolted can be better done but sleeves can split the casting vertically if too tight and drop into the cylinder if not tight enough in the casting fit. You have to allow a bit extra piston clearance too as the heat doesn't travel as well through the new assembly. This was always an extra thou in the trade years ago and I don't see why things change in that area. IF your barrel is bored too thin chuck it and get another or use a thick sleeve welded top and bottom to something substantial. A really thin spigot isn't enough to weld to. You can step the sleeve (larger) on one end and weld the other sometimes. Perhaps we should be casting some new cylinders. A single cylinder for most OHV's is not rocket science , especially the quite simple Ariel types. Nev

[Graeme.crawley]

Would three mm be required for a Huntmaster? Mine must've thrown a rod and smashed the barrel below the flange so someone bored and sleeved it leaving the jagged lower barrel sort of encasing the sleeve. I doubt there is 3 mm but it is only 325cc per pot, would that make a difference? I kept the compression at standard but it is pretty gutless, would quite like to put the higher compression pistons into it but fear the flange may break like this sloper. I also have another barrel with the same problem and the previous owner cut the jagged lower barrel off flush with the flange darn his eyes but what I can see as a result of his efforts is that the barrels are not central in the casting - very little on one side and much metal on the other side and this is not obvious from the top and possibly even that visible underneath when the lower barrel is intact. It must be easy to end up with wafer thin metal on one side if boring it. Graeme

[john.whiting]

The early A10 has a reputation for cracking the flange,the later square barrel being called the "thick flange type".However there is a lot of extra metal in twin barrels to hold them together,even if lined.An exception is preunit Triumph 650s,the barrels cant be lined without cracking into head bolt holes.The unit barrels had wider spaced head bolts.

[nevhunter]

The part carrying the load is the flange and above. The spigot below is tapered off to a fine edge in vertical twins and is not easy to do a neat job when sleeved so just remove the very thin edge so some of it doesn't peel off and fall into the motor. The sleeve doesn't add to the strength to any extent unless it's thick and welded on both ends. A complex process only resorted to in cases of no other way of getting a new part. Always ensure the top face of the crankcase is flat and the cylinder also and I don't recommend THICK gaskets in that location.. Nev

[Simon.Gardiner]

Graeme:
The 'problem' A10 barrels are the standard 'square-fin' ones when used with an engine tuned to Road Rocket/Super Rocket etc spec - the higher-tuned engines needed more meat around the barrel base, hence the 'thick-flange' barrels.
The standard barrels don't seem to have any problems coping with the later Gold Flash spec (7.25:1 'flat top' pistons and 356 cam) even when sleeved. I'd reckon there's a good chance your barrels will be fine.
That later Gold Flash spec is also the Ariel 'export' and 'sports' spec; the Cyclone spec had the higher 8:1 compression ratio, with standard barrels, and I don't think these have an issue with barrels splitting either. However, if you're going to go above 7.25:1 and the 356 cam you might be advised to use the later big-bearing crank and rods but that won't fit straight into early crankcases....
I've got a link somewhere to a discussion in a BSA forum about the problems sleeving the BSA 'thick flange' barrels - bear in mind that some people are using very high states of tune with these. The more successful 'fix' was to braze the sleeves in the barrels at the top and bottom - similar to what Nev is describing with welding, but it might be easier.

SG

[nevhunter]

I agree with the Brazing method. Cool it all out slow in slaked lime. Use nickel bronze as it's stronger than iron and is often used with racing car frames and altering bike frames. Hot job . Get the liner thickness right, leave a gap top and bottom and fill it with braze. Preheat carefully and don't let cool wind blow on it. It won't be in the ring travel area and you bore and hone to size after all this is done. Alloy barrels are probably more problem overall than iron. Iron with an alloy head is the best combo, from a practical viewpoint for twins and you will see plenty of examples of it. Nev

[PaulMeredith]

Hi . There is an alternative to fitting a liner to recover a barrel with a worn out +60 bore. Fit a larger diameter piston. I believe the +60 piston max oversize became a sort of industry standard as the weight increase due to thicker skirt was just about acceptable. Oversize pistons being heavier as they were machined from the same casting. I do not know if there is maximum over capacity limit imposed by Vehicle Licencing. I am much happier to fit a larger piston as the metal loss to the barrel structure is far less than fitting a reasonable thickness liner. As my main Ariel interest is with short stroke engines 86.4mm bore std. there are very few original pistons available, may as well say none. The originals if they can be found are far from ideal as they have no oil control ring and are parallel and round skirt. Without modification to taper and oval the skirt the clearance required is massive. The modifications and fitting an oil control ring can be done but it does not help if the bore is oversize. There are many pistons available with suitable bore sizes but the deck height is too short on many. MSS Velocette pistons are about perfect but as STD is 86mm don't go big enough in oversize and are a bit too heavy.
Pistons have shrunk in height over the last 80 odd years until now they approaching the shape of a thick penny. In the 70's they still had a reasonable skirt length. After many hours searching piston dimensions I found a possible one but the deck height was approx. 13mm short. It just happens that a VB or VG rod uses the same big end as the short stroke engine but is 12.7mm longer. Problem solved. They are available from STD 87mm to 90mm diameter. 88mm fits a honed out +60 barrel if not worn too much. Also with different compression ratios. A 11:1 specified gives a compression increase with an SF head of approx. 1 ratio.

Piston is specified for an XT TT SR Yamaha 500. I use Wiseco made ones they are forged. 20mm little end so needs a new bush in rod. Wossener also make them.

Typical part number 87.5mm bore 10:1 cr ( in original xt engine ) 4045M08750 WISECO

Weight is less than standard at 469g complete 87.5 bore 10:1 compression. The lightest original piston I have is std. bore slipper piston which weighs 530g
We have one engine running on an 88mm and all seems well so far.

There is no reason I can think of for not having the more popular pistons ie. 81.8 diameter made in larger over sizes. Provided the tooling is correct there should be minimal increase in weight. The cost of a having a liner fitted well could exceed the cost of a piston.

Making new barrels is the answer but a good oversize piston is a cheaper option............

Paul M

[nevhunter]

While the 500 OHV barrel is much stronger than the 350, (thicker in the walls) eventually the position of the head bolts tends to limit the bore size especially with alloy barrels. The Vincent pistons are std at 84 mm with a comp height of 1and19/32 inches so you need a shorter rod. or pack it up and have a bit more trouble fitting it in the frame. Nev

[john.whiting]

A liner with 1/16 wall thickness will need the barrel bored a bit under 86mm,so any bigger piston is going to be weaker than a liner.If the liner is transition fit and loctited,as is a common practice on automotive work,the liner will add some strength to the assy,how much the question.One thing I mention is that when a barrel is bored,the top is often taken as the mounting surface.Now if someone has been ripping into this with grinding paste lapping a head ,the top will no longer be square to the bore.To use the lower register,it is necessary to make up a collar to fit.Now who is going to bother with this for a" one off" rebore.Here a new problem emerges if some one has decided to increase the compression by shortening the barrel.Neither top or bottom is now square,and the barrel must be mounted on a mandrel.But what if a cockeyed rebore has already been done.The simple answer is a sign reading"We do not work on motor bike parts".