Large out of spec tappet clearances

[Guest]

I have measured the my tappet clearances.

What surprises me is how big the gaps are

The specs are 0.03-0.08mm

......IN..........Shim........EX...........shim
1 0.140mm...2.3........0.135mm.....2.6
2 0.130mm...2.3........0.115mm.....2.6
3 0.140mm...2.25......0.160mm.....2.5
4 0.125mm...2.35..... 0.125mm.....2.45

So all of the shims need to changed for the next size up to bring them into spec.

What confuses me is why are they so far out.
I know the numbnuts who had the bike before me didn't check the clearances. He had the bike for 3 or 4 years and about 20000km.
So they must have been at least this far out and possibly further out.

Apart from a cockup is there any reason for them to be that far out?
Cheers

[TheCafeKid]

Carbon trapped under the valve can hold them open, causing the clearances to be larger. I had a 750 8v motor that i had to go down THREE sizes on to get it into spec. Eventually, the valves, i would assume, would be so far open all the time that the bike would have trouble starting, if it would start at all...

[Steve]

So all of the shims need to changed for the next size up to bring them into spec.

Actually, it would be nice to go a size and a half for EX3.

If you had a 2.55x, it would bring that down to 0.085 or so, right at the top of the range with the rest of them.

.

[49er]

I have measured the my tappet clearances.

What surprises me is how big the gaps are

The specs are 0.03-0.08mm

......IN..........Shim........EX...........shim
1 0.140mm...2.3........0.135mm.....2.6
2 0.130mm...2.3........0.115mm.....2.6
3 0.140mm...2.25......0.160mm.....2.5
4 0.125mm...2.35..... 0.125mm.....2.45

So all of the shims need to changed for the next size up to bring them into spec.

What confuses me is why are they so far out.
I know the numbnuts who had the bike before me didn't check the clearances. He had the bike for 3 or 4 years and about 20000km.
So they must have been at least this far out and possibly further out.

Apart from a cockup is there any reason for them to be that far out?
Cheers

Shane, the PO possibly mistakenly set them to the maximum 16v motor clearances. Their range is 0.08 - 0.13mm. Otherwise it was just "fluctuations".

[psyguy]

i'd say either a mistake when setting them up or this:

Carbon trapped under the valve can hold them open, causing the clearances to be larger.

[49er]

i'd say either a mistake when setting them up or this:

If all those inlets had carbon buildup on their seats, the engine would be in a pretty sorry state!! How carboned up do the exhaust ports look?

[GregT]

I'm picking a mistake by the PO - in my experience the unleaded available here in NZ when used in big aircooled motors will cause a very slow recession - closing up the clearances rather than opening them.
If they're that big now - what did he set them to originally ?
Are you OK for shims - I'm not that far away and have a reasonable stock.

Greg T

[psyguy]

If they're that big now - what did he set them to originally ?

yeah! even now it must be a pretty rattly valve train! (mind you i like that sound ).

[KiwiGS]

Actually, it would be nice to go a size and a half for EX3.

If you had a 2.55x, it would bring that down to 0.085 or so, right at the top of the range with the rest of them.

.

So a 2.55x is about halfway between 2.55 and 2.6 yeah?
I could get one of my 2.6 lapped down to 2.575

Shane, the PO possibly mistakenly set them to the maximum 16v motor clearances. Their range is 0.08 - 0.13mm. Otherwise it was just "fluctuations".

I think you are right the PPO may have used the wrong specs.
Not sure I can blame the "fluctuations" for this one.

Carbon trapped under the valve can hold them open, causing the clearances to be larger. I had a 750 8v motor that i had to go down THREE sizes on to get it into spec. Eventually, the valves, i would assume, would be so far open all the time that the bike would have trouble starting, if it would start at all...

The bike ran ok and was quite easy to start, it was standard when I got it. The Plugs were the right heat range and the carbs, airfilter and airbox were all standard.
Also the exhaust ports did not appear to have any more carbon than I would expect.
So it seem unlikely that it is carbon, but never say never I guess.

Cheers

[bwringer]

If you were in the US, I'd say that some long-ago nosepicker used thousandths of inches instead of hundredths of millimeters to set clearances. It's a very common error here in the metrically retarded US of A.

.003" = .076mm
.008" = .200mm

Have the mechanics and machinists in NZ also clung to outdated systems of measurement based on barleycorns and oxen?

[GregT]

By and large, yes, we have. You don't throw out good micrometers just to avoid doing a little arithmetic.
And,yes,I still pace out my acreage before climbing on this interweb thingy.

Greg T

Old & crusty machinist & engine builder reluctant to use a system imposed by Napolean

[Steve]

So a 2.55x is about halfway between 2.55 and 2.6 yeah?
I could get one of my 2.6 lapped down to 2.575

Please don't do that. Some here have reported success, but the shims are hardened, so whatever you do, you must either maintain that hardness or restore it when you are done. If you went to a 2.60, you would still be in spec, just that it would be a bit less than the others.

.

[49er]

If you were in the US, I'd say that some long-ago nosepicker used thousandths of inches instead of hundredths of millimeters to set clearances. It's a very common error here in the metrically retarded US of A.

.003" = .076mm
.008" = .200mm

Have the mechanics and machinists in NZ also clung to outdated systems of measurement based on barleycorns and oxen?

Don't be so harsh on your countrymen. We were plunged, kicking and screaming into the metric system in '67. It wasn't all bad. Government and businesses in general made an unexpected windfall when amounts that didn't directly convert were surprisingly, you guessed it, "rounded up".

I believe that you are probably correct too, with your assumption above.

[GregT]

Re grinding shims.
In my experience - 20plus years of grindng these - they are hardened right through.
I ensure that the untouched side is against the cam.
I've never had a problem with ground shims.

Greg T

[49er]

Re grinding shims.
In my experience - 20plus years of grindng these - they are hardened right through.
I ensure that the untouched side is against the cam.
I've never had a problem with ground shims.

Greg T

Yeah, if you don't get them too hot, it's not a problem. Light cuts and/or coolant = no problem!

The only draw back is that future owners /tuners need to be measuring each shim to correctly size them to make adjustments. I do this anyway and have found 2 incorrectly marked shims so far. Also, it's nice to confirm the actual size of the x marked shims. In my experience, they usually range 0.01 -0.03mm above the stated size.