Laverda 500 cylinder head

sfcpiet said:
Paul,

As with all 500 heads, and Laverda heads in general for that matter, the problem compounds itself from recessed valve seats and wear on the valves themselves. Especially the 500s are fickle in regard to well-sealing valves, one crappy seat and you'll be hard put to achieve any kind of steady idle due to the extreme lack of flywheel effect. To achieve a good seal, the old valves will need to be ground and the seat inserts re-cut, with the valves being lapped-in afterwards. When you're through with that, the necessary shim will have shrunk from 2.10mm to around 1.80mm, with luck. If the guides require replacing, even more metal will need to be removed from the seat inserts. Apart from the thin shims, which aren't really a concern regarding reliability or spring pressure, the whole valve seat geometry is out the window. The 500s aren't blessed with extreme torque and power to begin with, recessed valves will further limit power output and driveability.

Miguels head will require new seats and perhaps new valves and guides. Repairing the cam bearings will close up clearances even further, possibly the "correct" shims will end up even thinner! With new seats protruding slightly into the combustion chamber, shim size can be restored and flow is greatly enhanced (see modern car 4-valve combustion chambers), releasing quite a bit of additional power to boot, making the riding experience all the more pleasurable. The needle race can be reclaimed by laser welding and regrinding, the bushes are a simple alloy or bronze item that any machine shop can knock up after the cam journals have been tidied up. All in all, a quite straightforward but lengthy repair that won't be cheap.

Motorcycle maintenance is (should be) something normally measured in hours, not weeks and months searching for indescript shims or even resorting to having to make new ones. Keeping an old dog running by the skin of its teeth isn't my idea of fun motorcycling. Do it once, do it right.

piet
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Yes Piet, I hadn't taken into account the necessary work on the seats and valve gear. Thanks for the reminder.

The protruding valve seats reminds me of work I had done on the head of a triple I was rebuilding for somebody during the big lead free scare. I had "lead free" seats put in by a well known firm in the UK advertising the world over. A right mess they made of that.
I rebuilt that triple on an exchange basis; You do my triple, I'll do your bathroom. The triple was a mess as in rebored with new pistons but a crank with blown centre mains and thumb size bits of piston in the crankcase. It had been rebuilt by a professional. A few interesting bits came with that bike, an ex Bol d'Or fairing and a works big bore 3/1.
The bathroom was well done.

Paul
 
Miguel,

Ordering "standard" valve seat inserts is a waste of time and money. They are configured to fit in the stock bore of the head. Just removing the old seats will require that this bore be dressed in order to offer a proper press/shrink fit (this requires specialist equipment, experience and knowlege of the materials involved, not something that should be attempted with your cord-less Black&Decker on a Saturday arvo ;) ). Stock seat inserts will fall into the re-dressed bore, not what is needed. I work only with insert blanks that I machine to size. The projection of the seat inserts sorts itself during the machining process, no hard and fast rule. Depends on the actual working, not overall, length of the valve and where you want to have the sealing surfaces on the valve. Different approaches for different uses of the engine, racing seats look a lot different to what you'd expect for long-term road use. Racing seats don't have to last as long, other priorities.

Reckon your NOS cam bushes will have almost as much slop as your old ones, especially at the journal where that knackered bush was fitted. The journals generally wear more than the bushes.

I use laser welding only for these type of applications, I have sucessfully reclaimed MV Agusta crank journals in this manner. The welded and re-ground surface has a hardness of around 60-64 Rockwell, much the same as a ball bearing. Laser also has the advantage that there is almost no risk of heat distortion. I don't see any problems using it for such a relatively low-stress area as the centre cam bearing. But the damaged bit cannot be simply patched up. The entire journal needs to be ground smaller, a continuous(!) bead of weld laid down which is then re-ground to size. Easier and cheaper to find a replacement camshaft.

Nothing is as easy as it seems... especially regarding Laverda 4-valvers.

piet
 
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Laverda 4 valvers. What a waste of valves. And two cams to boot. :p
Couldn't that centre cam journal be turned down and a hardened chrome ring shrunk on?

Paul
 
sfcpiet said:
Miguel,

Ordering "standard" valve seat inserts is a waste of time and money. They are configured to fit in the stock bore of the head. Just removing the old seats will require that this bore be dressed in order to offer a proper press/shrink fit (this requires specialist equipment, experience and knowlege of the materials involved, not something that should be attempted with your cord-less Black&Decker on a Saturday arvo ;) ). Stock seat inserts will fall into the re-dressed bore, not what is needed. I work only with insert blanks that I machine to size. The projection of the seat inserts sorts itself during the machining process, no hard and fast rule. Depends on the actual working, not overall, length of the valve and where you want to have the sealing surfaces on the valve. Different approaches for different uses of the engine, racing seats look a lot different to what you'd expect for long-term road use. Racing seats don't have to last as long, other priorities.

Reckon your NOS cam bushes will have almost as much slop as your old ones, especially at the journal where that knackered bush was fitted. The journals generally wear more than the bushes.

I use laser welding only for these type of applications, I have sucessfully reclaimed MV Agusta crank journals in this manner. The welded and re-ground surface has a hardness of around 60-64 Rockwell, much the same as a ball bearing. Laser also has the advantage that there is almost no risk of heat distortion. I don't see any problems using it for such a relatively low-stress area as the centre cam bearing. But the damaged bit cannot be simply patched up. The entire journal needs to be ground smaller, a continuous(!) bead of weld laid down which is then re-ground to size. Easier and cheaper to find a replacement camshaft.

Nothing is as easy as it seems... especially regarding Laverda 4-valvers.

piet
Click to expand...
Hi Piet,

Thank you for your honesty. Of course I am not planing to do that myself, despite I would love to, and “some day” I will do it💪🏻. But going to the engineering shop with a good idea of what has to be done, helps a lot. I am sure is a complex thing, but I have seen people on you tube doing it with all kind of manual tools!🤣🤣 (all from south america of course)

Regarding the seats, Wolfang is giving to me a set for free as I am making a big order now. I don’t know if they will be oversized or not, but if they aren’t I know that is not the issue as my local workshop do them themselves.

What should be the clearance between cam-end vs bush?

Regards
Miguel
 
MIguel, to add to Piet's excellent summary of valve issues, I'd also check for flatness of the head as they are known to warp badly. If you find it is warped and you do decide to skim it, don't forget to re-machine all the cam bearing holders as these will then be out of line.

Good luck !!
 
Last winter I started a journey with my Harris 600 head.
The thread off both sparkplugs were worn out and bushes were fitted.
Taking the plugs out means new bushes.
Besides the thread there were cracks between the valveseats.

Finally after welding, new valveseats and fitting 10 mm sparkplugs (all thanks to Gijs van Dijk) we made the inlet airflow properly for fitting 40 mm dellorto’s.
 

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Nice work, apparently what all these 4 valve twins need, it was also a problem with the Yamaha 4 valve twins then.
Bloody big carburettor for a 300cm3 cylinder.
 
Well, my Atlas has twin 40mm chokes, one for each 300cc cylinder. My 250 Modern Husky came with a 37mm Flat Slide Kehan, BTW that required lots of mods to Carburate cleanly. I think they spec them for as much power as possible and then they are incredibly touchy down low, easily bogging, as a result.
 
Tippie said:
Nice work, apparently what all these 4 valve twins need, it was also a problem with the Yamaha 4 valve twins then.
Bloody big carburettor for a 300cm3 cylinder.
Click to expand...
Yes it is. Like Vince says, all for power.
Before this work it had 63/64 bhp at the rearwheel.
I hope all these beast are still there😎
 
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