Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board A65 barrels cracked at center bolt

I finally decided to pull the head on my 68 Spitfire to try and address the oil coming up the head studs. There are definitely signs of oil on the head gasket near both right-side studs but what immediately stood out to me was the oil between the head gasket and the top of the barrels, in between the two cylinders. Looking closely, it appears that the center bolt hole is cracked on both sides:

(note that the cylinders are sleeved so no chance of the crack going farther)

Other than the oil weeping up the studs, the bike worked fine. I don't have the cash to find replacement barrels and the pistons / machine work needed to get it replaced. Any "temporary fixes" I can use to get it to better clamp down as-is? Any major concerns with continuing to run it in this state, other than a bit of a mess after every ride?

Can you tell how deep ( in length downwards) the cracks go ? This would influence any suggestion i may have ,,, i dont recon its a throw away just yet.

Looking at the photo, the sleeves are almost into the bolt hole leaving it very weak. I would be worried about how much meat is left above the base flange

It looks to be cracked all the way down on both sides. I tightened the bolt by itself (not fully torqued), and the cracks don't seem to widen, for what that's worth.

If it was running ok before, then just put the thing back together using
some welseal on the annealed head gasket.
BUT just remember what it's like before racing any hyabusa's
Those liners look a bit thick to me but it may be just the photo angle.

Use some wicking Loctite on the cracks, 290 is one but there are other grades more likely to be more applicable to a crack under pressure, also use welseal or some other sealant on the gasket for insurance.

If oil is on the head gasket and barrels I would be inclined to check the barrel top for flatness and also the cylinder head. It's not uncommon for these parts to become distorted over the years, hence the oil leaks.

Maybe you could try placing the parts on a glass plate with some engineers blue added, any high or low spots should then be visible. If there is a problem, you should take them to an engineering shop for rectification.

Not too sure about the cracked thread in the barrel, one part of me says to use a recoil/rethread insert which will provide a much stronger fixing. However, I'm not sure if this will weaken the barrel any further.

Don't like it. Real thin in that area.

MarcB,

Did You check the headbolts tightness (retight) 250 miles after rebuilding? That is very important! You have to release each bolt and the retight to specified torque. The center bolt tightness is very important. Even if the thread is ok, it sometimes leak if the after tightning has not been done.

So many a65s blew up over the years that cylinders aren't rare.

I'd look for a good used one. Bring an inside mic or caliper to check bore sizes. You might find one needing only a .010" bore clean-up.

I have thought a bit about this complex issue.

1. my opinion is that the cracks were in all likelihood caused by some "machinist" using to great an interference fit on the liners thereby causing a tension stress point ( an anathema to cast iron )

2. a crack like that all the way down wont be from overtighting ,
3. helicoil would be worst than useless and i dont think just by looking that a solid thread inset is the way to go no diameter left.

4. I consider the oil seepage has little to do with the cracks as such but definitely fill them with proprietor Loctite or something

so what to do?

1, examine thread form as best you can, put a bolt back in and screw it down maybe 10mm and see it it feels like it wants to tighten by hand , if the tread form is ****ed sorry its toast (economically)

2, get it checked for flatness use the glass plate bearing blue method OR just hold it up to the light with a good straight edge as a rough look at it first

3. resurface the barrel and head to MINIMUM cleanup ( that crack wont cause problems with the function of the thread )

4. bolt it all back together and do a compression test after 1000 miles or less if you cant forget about it hahhahh

Having run the head against sandpaper on a glass plate, it definitely needs a skim. My fear is that, in its current state, it's inevitable that it will leak and eventually warp.


Not sure of exact mileage but, yes, retorque was done.

Mileage on current bore and pistons is 2300 miles so would rather not throw that away if I can salvage it

Bolt goes in normally, easy by hand for about 1/2 the threads, then with hand tools but without too much force. I'm able to torque it down with the head in place (not stripped)

Thanks for the input. Looks like I need to book a local machinist for the winter.

skimming head and barrel isnt a big job ... just make sure you tell him MINIMUM CLEANUP .... run a tap ( if you have one, if not nevermind) down all the treads to get rid of 60 years of crap in the threads which will affect your torque reading

seriously dont overthink it , it will be fine.

Find another cylinder.

Busted, that's what I told him too, but he seems determined to make a silk purse out of a sow's ear.

Well the OP stated :
" Mileage on current bore and pistons is 2300 miles so would rather not throw that away if I can salvage it"

personally i would not call that a porcine ear .... I applaud the OP in his conservation attitude of salvaging good parts with a minor NON FUNCTIONAL BLEMISH

I know the prevailing mentality is dump it in the land fill and get another but thats not how i roll

fixing things is part of the whole classic bike ethos if you ask me .

I'm glad this has been mentioned especially since the bike is a highly tuned Spitfire.

The oil leaks from the head joint aren't nearly as worrisome to me as the possible damage from the barrels separating just above the base flange because of those thick sleeves.

Also, I've seen sleeved BSA barrels crack between the cylinders on the underside too. Don't forget to look closely there as well.

Well, I repair as many small bike parts as I can salvage, but something as critical as cylinder barrels is different.
SLEEVE them, yes, Attempt to weld cast iron, no.

There is a special technique used to weld cast iron, including pre-heating the part before welding, and burying it in sand for SLOW cooling afterward.
Even then, there's no guarantee it won't crack again. It is a job for a specialist in this.

If you really want to save that cylinder block, best wishes, and good luck.

The best solution would be a set of Nikasil plated alloy barrels
Lighter
Stronger
and better heat dissipation

If the bike is ridden hard then replace the barrel. if it's just putted about like many
are now, put some welseal or similar on the head gasket and put it back together.
It was ok before other than the oil, so why should it not be now?

The liners look like car ones to me and are too thick really but not the end of the world.
Just bear that in mind when you see the tacho at 7000+
The reason for the oil may be the liners are moving, it's not unheard of.

The '68 spitfire was very much the same as the lightning so not really highly tuned
unless worked by the owner.

the reason the liners "look thick" is probably because they are a T shaped cylinder as is standard practice. only way to know is measure at the bottom of barrel and at the top ... probably around 3mm difference in diameter

none of which will weaken the casting etc ... the holes dont go full depth ya know ... it is serviceable if it if ground flat and the head as well

Agreed, the best liners are t shaped, however, i've seen plenty that are not.

There are basically two ways to sort out this problem.
Firstly the "proper" way is to get a replacement barrel etc etc.
However you say that you don't have the money to do that .
This reminds me of "back in the day" in the 1960s in UK when we never had money for anything except beer and had to improvise.
The key here is that you say that the bike went well except for oil leaks.
So in your circumstances I would do as Kommando suggests-- wick a high temperature wicking Loctite down the cracks and the as Kommando and Nick say-- a fairly generous helping of Wellseal on the head gasket.
torque up the head bolts, take it for a short ride, let it cool and then retorque the head bolts.
Another short ride and retorque again.
Then you should be good to go----to the nearest pub but not to the racetrack.
Just my two cents worth of course.

Where is the oil coming from? There is no oilway or oil containing cavity in that part of the cylinder

A '68 Spit was originally 9 to 1 with 32mm carbs. A lightning was 9 to 1 with 30mm carbs.
Top hat or flanged liners are useful for repairing a cracked sealing surface and for keeping the liner from moving around. We often use them to recover a Jag block that has a crack between two cylinders that ruins the sealing surface. These type of cracks however aren't through a threaded hole.

If the liners in the presenter's bike are flanged, it would probably have been better to use a wider flange to completely cover the cracked area.

If the liners are NOT flanged OR even if they are, they could have moved downwards slightly, reducing the sealing integrity between the bore and the stud holes. This could allow leakage up the studs like the OP is experiencing.

We need some photos or measurements of the bottom of the cylinders from the OP.

Thanks