Bonneville America Forums Forums Technical Forums General Tech Pat's shim calculator

I'm checking and adjusting the America's valve clearances using Pat's (thanks) calculator. I was wondering why the default clearances in the calculator for both the exhaust and intake were in the middle of the limits (.175mm intake and .275mm exhaust) instead of the lower limits since the shims wear thinner and thus the clearance gets greater over time. Would it hurt to substitute the lower limits (.15mm intake and .25mm exhaust) in the calc???? This is (as you can tell) my first time to do the valve check. In my efforts to get it right and not destroy any pricey bits, my nerves are slightly frayed... I have read tons of info here and combed the service manual just enough to get my pea brain clogged. All tips and info will be greatly appreciated. Oh, I had one intake gap under the limit at .13mm. The America has 14,000 miles and no adjustments until now. Just FYI the gaps were
EX .27 .28 .33 .31 mm
IN .20 .23 .18 .13mm
The .13mm gap has me a little concerned about what it must have been from the factory.

The middle of the clearance range is what you want to shoot for. Shims wear, yes , but so do valves and seats. If you can't hit mid range dead on don't be concerned as long as it falls close.Don't worry about a tight reading when you first checked them as long as you didn't have one so tight it wasn't closing.

If you didn't remove the engine side cover be sure NOT to move the engine while it's apart. Once you have the new shims in and cams back in place turn the engine a few times and recheck clearances. Also pay close attention to the marks on the cam gears and be sure you use the right ones for the right cam.

The valves can "sink" into the head as things wear, causing clearances to decline rather than increase. That's why you shouldn't intentionally adjust them to the tight end of the spectrum.

I (sucessfully)finished the intimidating (for me) first time valve clearance adjustment. Thanks to all for the advice and especially to Pat for the shim calculator fully equipped with the handy-dandy inches to mms converter for those of us with non metric micrometers. Here are the numbers.(mm):
Old clearances
Exhaust .27 .28 .33 .31
Intake .20 .23 .18 .13
Old shim thickness
Ex 2.781 2.809 2.832 2.863
In 2.755 2.705 2.753 2.809
Pat's calculator says
Ex 2.776 2.814 2.887 2.898
In 2.781 2.760 2.758 2.764
Actually used (measured)
Ex 2.778 2.809 2.885 2.905
In 2.781 2.753 2.755 2.766
New clearances
EX .28 .28 .28 .27
In .178 .178 .178 .178

The America is running great and has a new (although stock) air filter. No pricy bits were destroyed during this project thanks in part to horror posts I'd read here about putting things (cams ) in the wrong spot, snapping bolts, bending valves and so on. The Triumph service manual along with numerous posts on valve adjustments and much deliberation helped me (and the America) get through the job unscathed. After doing the job once, I won't think it"s a big deal next time. Again, thanks to all (including D&D cycles in Norfolk for the fast parts and good advice) and Pat.

glad it all worked out. It does appear to be intimidating the first time, but afterwards you have a great sense of accomplishment and feel about $250 richer as well.

My biggest thing with the valve job is the fact I don't have a misc. box of shims in my shop to pick from. Had to run over an hour away to get them and then had missed 2 of them and had to go back for the right ones. Good thing Herm traded the 2 wrong ones for the 2 I needed. The 2 local Yamadog dealers here didn't have what I needed, one had no 25mm shims at all and acted like I was from another planet when I asked for them and the other had them but not the thicknesses I needed.

Triumph only carries shims in .025 increments but when I was at the Yamaha shop looking I saw that you can get much finer than that.I don't remember what was available but I do remember sizes in between.

Gregger, the 2.925 is an available Triumph shim. Order the 2.925 and measure it. The local Yamaha dealer in Lynchburg, VA only had shims in .050mm increments, so I went with the Triumph (I think) ones in .025mm variations. The reason(s) that the new shim thicknesses I used aren't in exact .025 variations is that they didn't measure exactly as they were marked and or that my measurements were converted from inches to mm by Pat's handy dandy convertor. Whether my micrometer is exact or not, it is the same one that I measured the old shims with. As others have posted, you should measure new shims and not take it for granted that the marked measurements will agree with your micrometer. Since the new shim thickness (thanks to Pat's calculator) is determined from the old gap, old shim thickness (measured with my micrometer) and new desired gap, measuring the actual thickness of the new shims with the same micrometer is important to the results. There could be enough difference to cause you to use a shim in a different location or to reorder or exchange for a shim closer to what you need. As I said earlier, this was my first valve check/adjustment for the America and I wanted to get it right without ruining anything. This forum and it's members are great.