Laverda 500 valve stem seals

[Lyndoneil]

Does anyone know where I can buy a set of replacement stem seals.
Reassembled the engine (again), runs lovely now, but smoking fairly heavily from left side cylinder, I suspect one or more valve stem seals have dislodged
Although I will do a pressure test on the cylinders.
When I was rebuilding the cylinder head the stem seals preferred to grip the valve stem rather than the valve guide, I believe they are Honda stem seals as when supplied more suitable replacements was unavailable.
The only identification on the receipt is 097, were originally supplied by Richard Slater, who sourced them from elsewhere, not complaining, just explaining.
I've since learned that it's not totally uncommon for the necessity to glue the seals to the valve guides in some instances. What's your thoughts on this?
If I am going to need stripping the cylinder head again, then I might as well replace them with better seals if available.

 

[KERMIT1200]

Hi Lyndon,
Wolfgang or OCT should have some in stock . They had a load re-made.
I have some, but off racing in France today so can not help you straight away.
Andy

 

[Dellortoman]

If you'd rather not pull engine out of the bike and remove the cylinder head just to change valve stem seals, there's an easier way. You do it without removing the head and with the engine still in the bike. It's quite easy and works very well. It also saves a heap of time and won't disturb your newly fitted head gasket. I replaced a set of valve springs a while back without removing the head (it was in a 6-cylinder car but makes no difference to the method).

Once you have removed the cam cover and camshafts, turn the crank so the piston is somewhere near BDC on the cylinder you're working on, then feed some soft and flexible rope into the spark plug hole until you have more than enough to completely fill the combustion chamber. Choose a thin enough rope, about half the diameter of the spark plug hole, so that if it happens to fall into the cylinder in such a manner as to loop itself into an overhand knot in the end (very unlikely, but possible), the knot will be small enough to pull back out through the spark plug hole. You also want something that won't shed a bunch of fibres into the cylinder. Venetian blind cord or para cord is good. Once you have enough rope in there, turn the crank until the bundle of rope jams tightly against the cylinder head and valves, stopping the valves from opening. You can now press down on the spring retainers to remove the collets and springs (you might need to invent a tool to compress the valve springs). That'll give you access to the stem seals.

I've heard that the same process can be achieved by feeding compressed air into the spark plug hole to hold the valves against their seats, but I think that method is riskier. If you crack a valve open a bit while removing the spring, you could lose cylinder pressure and drop the valve into the cylinder. Then you're back to the engine out and head off job.

 

[LaverdaIan]

You sure could try that Cam if your lucky, but for sure the best way is the tried and true professional way.. engine out, head off, remove valves etc. and replace seals. It is true that the 6mm Honda seals do work but need glue to lock them on.. not always successful though (ask me how I know) because the seals don't have the tensioned outer ring as fitted by Breganze and will pop off as you refit the valves. You are trying to glue something to an oily surface after all.. and what is a head gasket cost vs. constant failed 'easy' methods..
Modern solution is to refit with new lipped guides that Wolfgang, Red, Keith and others employ that have a retention lip at the top fit for purpose. Then the seals are fitted firmly and permanently. That is how you replace 500 seals properly.. struggled with the issue years ago and only best solution available.
Suggest you seek reliable advice to resolve the problem.
HTH

 

[Dellortoman]

I agree Ian. If the valve guides need to be modified to retain the seals, then yes, the head will obviously have to come off to remove the guides.

The reason I chose to replace the valve springs in my car (Datsun 260Z) with the head in place is that I had just had the head off to replace a blown head gasket. When I got the car going again it wouldn't rev out (I'd not had the car long so hadn't had a chance to rev it out before the head gasket went). I took it to a dyno guy who diagnosed weak valve springs. I didn't pull the head off again to replace the springs because it wasn't necessary. The rope method is a well proven and perfectly safe shortcut, and not at all unprofessional.
BTW, the dyno guy was wrong. It wasn't the valve springs. The problem was an electronic ignition that had been fitted by a "professional" who got it wrong. But that's another story.