Valve grinding on an sv650?

Hi all, first post, I have a problem with a k3 sv650 I bought, bike had been lying up for a number of years, so when I got it I turned it over by hand and found that the exhaust valves where leaking on the rear cylinder. On closer inspection the engine must have been lying with these valves open and a tiny bit of corrosion had formed on the valve seats. So popped the heads and barrels off and left them at a engineering shop, asked for the heads to have a light skim just to clean the surface and to grind the valves in. When I got heads back, I bought a gasket kit from suzuki, built engine together, turned over by hand and all 8 valves were leaking. So, pulled heads off again, ****ed off at this stage, dropped them back at engineers, waited to get them back, got them, rebuilt and guess what? leaky valves.

So, are k3 valves coated in something that they cant be lapped in or ground in? Im a car/van mechanic so know my round an engine. Just havent a stack of experience on motorbike engines.

[Bibio]

how do you know its the valves?

[Bibio]

oohh and did you check the shim gaps?

well!!! when you turn it over by hand with the engine sitting on the bench, I can here air escaping up the intake and exhust ports, also sprayed wd40 down and can see them bubbling. its def the valves.

yes checked valve tolerances, actually took cams off and turned it over whilst holding chains out and it still happens. its the valve seats.

[Sid Squid]

Seems odd that all eight are leaky, is there a position the engine could be in where all of them are open to cause corrosion as you've found?

Anyway, although I've never needed to do so on any SV motor I've attended to, even very high mileage ones, as far as I know there's no reason why you shouldn't lap the valves if they don't seal right, although if it were mine I'd examine the seats carefully to see if cutting rather than lapping would be a better bet.

PS. You sure you haven't got bent valves or if there's corrosion on the stems causing them to jam up on the guide? I've seen that on a motor that was unused for some time.

[Nobbylad]

Is it worth changing the stem seals as well?

[Sid Squid]

Ordinarily they would be renewed if the valves were disturbed - but they don't play any part in the valve sealing.

The valve stem seals keep the oil in the cam box and not puffing out of the exhaust.

valve stems seals were replaced. as it says in the origional post, there was only two leaky valves, these must have been lying open for a while. the 8 valves have only started leaking from i've had the seats cut and lapped in. no corrosion on valve stems. all opening and closing smoothly.

[embee]

As Sid suggested, lapping is a bit of a mixed blessing really. Cutting is a better engineering solution since it should (!) achieve seats with straight profiles, the problem with lapping is that it generally achieves reasonably well mating surfaces but they can be any profile, like 2 pieces of jigsaw if you like, full of ridges.

Valve and seat insert angles are specified with usually something like 0.5deg tolerance (normally 45deg nominal but not always), but the seats are toleranced "plus" and the valves are "minus" such that the contact surface is always at the fire side (cylinder) so you don't get a narrow wedge gap exposed to combustion, which leads to gas leaks, accelerated erosion, overheating etc. Lapping removes this condition.

Providing the mating is reasonably good they will bed in when first run anyway, production valves are not lapped (for reasons above), they sort themselves out.

If you are capable of dismantling the engine to that stage I'd say you are more than capable of lapping them yourself, then you'll get it right rather than relying on an unknown person who may or may not know what they are doing.

Use the finest lapping compound you can, use a few strokes back and forth (preferably a hand sucker type lapping stick rather than a machine oscillating type), turn it 1/4 rev, continue etc. After 1 rev clean off the paste, inspect the surfaces, should be smooth matt grey appearance. Try lapping with no paste and see if it produces a hint of polish to indicate where it's mating.

Using too coarse paste is a common mistake.

People use engineering blue to check seats but unless you are familiar with getting just the merest hint of blue on the surface it can very easily hide the reality (too thick a blue layer just looks even all round regardless).

Thanks for the advice, I think your correct, shouldve lapped them in myself at the start. I thought leaving it to a engineers wouldve been straight forward, but not if there not familiar with bike engines. Have spoke to a respected engine builder from this side of the pond and he's gonna do a leak test on it.

all part of a steep learning curve! Cheers all for input.