Problem lapping head to barrel on a '54 VH500

[nevhunter]

The alloy heads are much more of an issue than the iron ones were in service, but if you have one on your bike, that doesn't help as most keep things original. It's necessary to KNOW the surfaces match and will seal under pressure. You really can't LAP Aluminium. and it's pretty tricky to skim a stepped surface.like that is. Valve guides coming loose is an extra worry with the alloy variety. The guides are usually of bronze and have to be made oversize for any head that's done a lot of service.. I think if I was a person unfamiliar with this stuff, I'd take it to a "Recommended and proven Motorcycle Engine reconditioner" used to earlier machines. Not many want to even touch the stuff because of the time that it often takes and people's reluctance to pay for the time taken to do it properly..Nev

[Simon.Gardiner]

Phil Irving doesn't say to only use 'double grinding' for iron heads and barrels, his scope generally covers iron, aluminium and bronze so I reckon he's quite happy recommending it for aluminium heads on iron barrels.
We're still talking about getting a pressure joint on the spigot, maybe it's not appropriate to get too far into discussions lapping - the 'double grinding' technique seems to work pretty well.
There must be thousands of alloy head Ariels out there that have been (re)built and used time and again for decades without head gaskets and without any particular head-joint problems. I wonder what all those trials riders do? (Should have asked Sammy when we got a tour of his workshop last summer!)

SG

[david.anderson]

There is no need to lap to a double ground joint. I have always used a copper head gasket under my alloy head VH and there is a considerable gap to the cylinder flange. The head will not distort. My head gasket is a piece of copper that I cut from sheet and is perfectly round 82mm inner dia and about 1/4" wide and it sits on the cylinder spigot. I have used the same head gasket for the past 50 years and it has done well in excess of 200,000 miles. I simply re anneal the copper with every engine strip. The big issue with the alloy heads is as mentioned the exhaust guide coming lose. Mine has come lose several times which has been rectified with an oversize guide then a larger oversize guide, then knurling up an already oversize guide and finally sleeving with the sleeve being welded in and back to standard size. I wonder how long that will last. There is simply not enough depth of aluminium in the head for the exhaust guide. And the other 3 alloy heads that I have on other bikes all have had a lose exhaust guide. One was repaired before it came into my posession with both inlet and exhaust guides having a steel sleeve screwed in. While that head is on my HT and has not done a lot of work I have wondered how well the steel sleeves will hold up with the differing expansion.
David

[Roger Gwynn]

The gap twixt top of cylinder and underside of head should be .004/.015" (.1/.38mm) according to the drawings.

[paul.jameson]

Having had the loose valve guide problem several times in the 1970s I resolved in future never to use anything other than cast iron engines in my Ariels. Eventually I relented and have run Square Fours and the KH(A) successfully since. I have only had one single with an alloy head since the 1970s and I never rode it, but passed it to son Rob. He now knows all about valve guides coming loose!

[dennis.t]

After much grinding of the barrel spigot to head the gap between the head and the barrel is now 0.6mm having started off at 0.7. So, I have some way to go to get to 0.38mm (0.15")! Slow but steady progress.
I think I mentioned that the head is a refurbished one from Drags with new guides, valves and springs. The valve gear looks really nice and is smooth and the valves seal well.

Whilst I am new to Ariel's I am not new to motorcycle restoration having restored eight so far, all different makes including Norton, Honda, Ducati, Harley and Moto Guzzi. All bikes were 1980's or earlier with the Norton being 1964.
Dennis

[Simon.Gardiner]

Stop using that toothpaste!!

SG

[will_curry]

You really only need to grind it enough to get a good seal between head and spigot.
The gap between the bottom of the head and the corresponding face on the barrel
doesn't really matter until there isn't one and then you're in trouble.

I put a small amount of paste all round the spigot, put the head on in the correct alignment
and then only rotate it a few degrees either way. Once there is a nice matt face on both spigot
and head I clean up, put the studs back in the barrel, refit the head without murderizing the
nuts knowing that's a job I won't have to do again until I change the head or barrel.

[nevhunter]

Yes . The inner face is the one that seals and I wouldn't worry about the other on an alloy head. It's a bit academic. On the iron set up better heat transfer near the exhaust port is achieved over a larger area.. This is a non problem with Iron and totally satisfactory and requires no retensioning. Nev

[dennis.t]

I laughed at Simon's refence to toothpaste. I am actually using a small can of fine and course valve grinding paste that I bought 50 years ago at Gaggs in Nottingham. I am getting through it now though!
I think I will accept that I am not going to grind enough off the head for the faces of barrel and head to meet so I am going to stop now, satisfied that I have a good surface between barrel spigot and head. I have other things to worry about such as locating a rider's foot rest for a swingarm model.
I welcome all the advice.
Dennis