Valve shim sizes

[speedy231278]

Following on from recent discussion... according to the parts fiche, the 7.48mm shims (at least for the 30/35) come in 0.025mm increments, from 1.200 to 2.900mm. On another post, a shim marked 248 was remarked about, and I suggested that either it wasn't a Honda one, or it was a code, or there was some other reason it didn't tally with the fiche. However, while looking on eBay I've found a seller with a genuine Honda shim at 2.48mm, and the code matches that of the 2.475mm shim on the fiche. So, which is it? I appreciate that 5 thousandths of a mm is pretty miniscule, however it's still a reasonable percentage of the 0.06mm difference between the tight and loose ends of the spec on the clearances. Is it just rounded up for the sake of stamping less digits on the shim? Isn't there a similar thing with main jets where some of the even sizes like 108 are alleged to be 107.5, etc?

[bikemonkey]

I pulled some odd sized shims out of my engine, could be just rounding up, could be my not so expensive verniers being perfectly accurate.

And yeah main jets, I think 122's are actually 122.5's or something like that.

[VFRkieran]

Im pretty sure i have some odd sized ones too, when i get home i will check and see what numbers are printed on, most of them are directly from Rick oliver aswell.

[krisztian_andre]

Following on from recent discussion... according to the parts fiche, the 7.48mm shims (at least for the 30/35) come in 0.025mm increments, from 1.200 to 2.900mm. On another post, a shim marked 248 was remarked about, and I suggested that either it wasn't a Honda one, or it was a code, or there was some other reason it didn't tally with the fiche. However, while looking on eBay I've found a seller with a genuine Honda shim at 2.48mm, and the code matches that of the 2.475mm shim on the fiche. So, which is it? I appreciate that 5 thousandths of a mm is pretty miniscule, however it's still a reasonable percentage of the 0.06mm difference between the tight and loose ends of the spec on the clearances. Is it just rounded up for the sake of stamping less digits on the shim? Isn't there a similar thing with main jets where some of the even sizes like 108 are alleged to be 107.5, etc?

248 is the last three digits of the shim's part number it means diameter 2.475mm, this way they saved a digit.

[Neosophist]

248 is the last three digits of the shim's part number it means diameter 2.475mm, this way they saved a digit.

This isnt right, there are no 248 part numbers.

14905-KT7-013 is an example of an NC30 shim.

If memory serves me correctly I believe the factory fitted shims from Honda came in all sorts of odd ball sizes to make the clearances correct.

You can only buy increments of 0.025 but when new Honda put whatever in to make it exact, hence 238, 242 etc.

If you cant read the stamping on the shims then its a waste of time trying to get to 0.01 accuracy unless you have a decent measuring tool.

[arsey30]

The shims come in 0.25mm increments, so clearances can be set to within 0.125mm. They are marked 2.50, 2.38, 3.00 etc
I measure a marked shim with a digital vernier to check it's calibration before measuring unmarked shims.

[Neosophist]

0.025mm isnt it? (Sorry I missed a 2 on my original post, now corrected)

Only a small excerpt as its slow to type these.

14923-KT7-000 (1.750)
14924-KT7-000 (1.775)
14925-KT7-000 (1.800)
14926-KT7-000 (1.825)
14927-KT7-000 (1.850)
14928-KT7-000 (1.875)
14929-KT7-000 (1.900)

I use an old but expensive and accurate analogu micrometer to get accurate 0.01 readings (taken several times across the shim).

[speedy231278]

Starts 14901 (1.200) and ends 14969 (2.900). 0.025mm increments.

If you wanted a set of 16 of every size for your workshop, it'll cost the wrong side of six grand... lol

[arsey30]

Yes 0.025mm increments.
I have found that Honda set them up from new over a fairly narrow range of values, so not that many values are really needed.
My RC30 set has covered all my own and friends bikes that I have done or loaned out to over the last 20 years.
I do have to replenish stocks, as although I keep those taken out, common ones tend to get used up quickly.
Trouble is, although the shims are the same 7.48 diameter typical RC are 160, but NC 230, so I would need a new set.
It is handy having a shim bank as no need to take all the shims out to check their values to see if any can be swapped around, so strip/measure/order and set up a few days later.
Can all be done there and then.

[krisztian_andre]

248 is the last three digits of the shim's part number it means diameter 2.475mm, this way they saved a digit.

This isnt right, there are no 248 part numbers.

14905-KT7-013 is an example of an NC30 shim.

If memory serves me correctly I believe the factory fitted shims from Honda came in all sorts of odd ball sizes to make the clearances correct.

You can only buy increments of 0.025 but when new Honda put whatever in to make it exact, hence 238, 242 etc.

If you cant read the stamping on the shims then its a waste of time trying to get to 0.01 accuracy unless you have a decent measuring tool.

You're right of course, it's the marking on the shims, the part numbers are simply sequentuial...