Valve shim lapping

[ADSrox0r]

Since all the valves on the Aprilia are on the tight side, one out of spec, I figured on just lapping them down.

Any of our resident gurus have any sage advice/tips? I've done a bit of lapping before so not completely green to the process.

I know in the past some manufacturers have given specific warnings against damaging the shim surfaces, is this still a thing?
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[........]

I don't know about Aprilia but I've resurfaced valve shims on car engines by using a surface plate (or chunky sheet of glass, aluminium etc.) and very fine grades of wet+dry before finishing with micromesh. Significant scoring or wear can't be removed as they tend to be case hardened. Go through the hardened layer (no deeper than a few thou') and your shims won't last very long at all.

[ADSrox0r]

Yeah I figure they'd at least be case hardened. If I just lap the underside, the bucket side, and not the top face then at least that's not stripping away the area that needs it. Having the cam faces burring away the shim top wouldn't be a great thing.
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Pete.]

Personally I would lap the face with the size printed on it, then the next person won't get caught out. The main requirement is that they stay very parallel as the bucket turns in use. If you lap even a small taper (which you will without a jig) the shim won't rotate and you might get wear issues in the shim or the bucket.

We have a local bike shop that does exchanges for a few quid a shim. You might have too.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[ADSrox0r]

There's a decent bike garage at my work so I'll pop them in some zip bags labelled up and see if they're game.

The more I think about it the less inclined I am to the notion, like you say without a jig it's a gamble for the sake of 40 quid for new shims. I just like the idea of being able to dial in an exact measurement rather than having to go with the usual 0.05mm increments.
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Pete.]

There is no exact measurement, just in tolerance and out of tolerance, but I know what you mean. If I absolutely had to do it I would turn up a small holding block that the shim sits flush in and lap it on a stone.

Have you checked the shim sizes you have? You might be able to swap some about and only buy a few.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[Copycat73]

spoil the ship for a ha'penny worth of tar...

these things are really cheap ...

and your bodge would do jizzbunny / Bodywank proud...
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Whatever I post I have no citation and no intention of providing one..
caveat emptor

[ADSrox0r]

They're 30mm diameter, 3 are 3.8mm and one 3.5mm. Awkward size, can't seem to source any and the only places I can find that stock them model specific only go up to 3.1mm.
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Pete.]

Looks like you're not far from Malton you could try John at JW Motorcycles. If he doesn't have shims he might suggest where to get them.

Otherwise, a lick on a surface grinder would do the job. Local engineering firm?
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[ADSrox0r]

Could be worth a pootle up to see him, they're the UK distributor for Rapid Bike Racing modules which I rather fancied as an alternative to the PCV I have fitted.

I'll put a shout on the Aprilia forums, see if anyone knows a source or has swaps.
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Copycat73]

[Fizzer Thou]

Wemoto sell shims,but at quite a price

https://www.wemoto.com/bikes/aprilia/pegaso_650/95/picture/valve_shim_2.55_mm/

Luckily there are only four to sort out...or is it five?
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Just talk bikes.What else is there?

Always have a 'Plan B'

[Pete.]

Thickest shim they list is 2.90mm though and he needs thicker.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[........]

[ADSrox0r]

I see what you're saying; the valve seats have built up over the years and bigger shims have been put in to compensate. Lapping the valve seats would put the valve stem higher (or back to original height) meaning a thinner shim, or more to the point a shim of the 'regular' sizes available would be needed.

Let's just say for shits I went balls deep and lapped the seats, and forgive the ignorance, how do you then determine what size shim is required once re-assembled?
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Nobby the Bastard]

Don't shims get tighter (i.e. you have to put thinner ones in) rather than looser as a rule?

If you relap the seats, then they will get tighter still, requiring an even thinner shim.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

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[Pete.]

If his clearance is less than 0 shims are the least of his problems. He'd be looking at burned valves etc.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[........]

[Pete.]

An engine HAS to be running for a valve to get burnt. They don't pop like a fuse.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[ADSrox0r]

No Pete, what he means is that after lapping the valve seats if I were to put my current shims back in it would be likely that they would be too thick to give any clearance to be able to determine...well, clearance. A thinner set of shims would need to go in before you would be able to measure anything at all. For those purposes I guess I would just lap the shit out of the existing ones to get them down to be able to measure, then order a set once the clearance is known and bin the temporary lapped ones.

Sounds like a fuckload of effort for an old machine though.

I'm tempted to just lap the existing ones, get her running and sell it on and move on to the next project. Parts and wotnot have been a royal pain in the arse for the Pegaso.
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Pete.]

Ah right yes I got the wrong end of the stick.

What you should do before pulling the head and doing valve work is a leak-down test. If that gives a good result just do the shims and crack on.
____________________
a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[ADSrox0r]

A little internet-fu reveals that Aprilia lists shims up to 4mm, the range being between 3-4mm so I think this is indicative of mine being 'normal' rather than original suspicions of 'bodged in bigger uns'. https://www.fowlersparts.co.uk/parts/5692864/pegaso-650-pegaso-650-pegaso-650-1992-1996-pegaso-650-all/valves-t

Typically though, I still can't get hold of any in stock unless I order from out of the country and pay exorbitant delivery fees.
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[ADSrox0r]

As an aside for musing; would it be reasonable to say that a leak down test would be a useful indication of timing being off if you'd fluffed the cams on re-assembly? The given being of course you'd tested it at known tdc beforehand and no appreciable loss was present.
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Current bikes: '08 VFR 800 VTEC(yo) , '07 ZZR1400 Winter hack: '95 Aprilia 650 Pegaso Currently lusting after: RC30

[Pete.]

No, leak down is only done with both valves shut.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good