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Hello all,
I am assembling a motor using adjustable, steel straight-cut gears from CB. My gear lash (measured at the circumference of the cam gear with a dial indicator) is about .004-.005. The spec I have seen (presumably for helical-cut gears) is .000-.002. Is that the ideal lash for straight-cuts as well?

It occurred to me that one could build up the surface of the teeth with plating. A bit of research discovered that electroplating is no good for this purpose, as it is hard to control the thickness in small recesses (such as the root of a gear). But I talked to a plating firm about "electroless" nickel plating. They claim excellent dimensional control in such small areas, using a process that yields 55-57 Rockwell C hardness as plated, once it has been baked.

So... does this seem like a good idea? I'm not sure how hard the gears need to be. My thought was to build up the surface about .0015, which multiplied by two should take up about .003 of my gear lash. The cost would be their minimum charge of $132.

Or should I not worry about my loose gears? I'd rather not have a noisy engine (to say nothing of timing slop).

I'm interested in following your research, no personal interest as nothing I run is straight cut, but rather I'm tired of hearing the neighbor whine about how noisy his gear set is and how he should have done that (he looked into but didn't plate).

That should work.
You should look into doing something like a group buy, I suspect a dozen gear sets would cost about the same as one.

Have considered doing same on oil pump bodies to build up the OD, but having just one is impractical, altho std electroplating would work in that case. You could even do aluminum, and even DIY.

OK then, I'll do it. If anyone has a cam gear with a known, measured backlash about the same as mine ( a fat .004), come join the party and we'll have them plated in one batch. A bit more detail, for anyone looking to do this separately: Electroless nickel plating is done with either a "medium" phosphorous content (6-10%) or a "high" phosphorous content (10-12%). The higher P has better corrosion protection but is softer. Since this will be in an oily environment, corrosion isn't a concern and I will be using the harder, low P process.

The guy I talked to is Alberto Mani at Accurate Precision Plating in Houston, TX. Phone: 866-598-8063

In case you're interested in why standard electroplating is no good for tolerance control in small areas, I found this article pretty convincing:
http://www.materialstoday.com/metal-fin ... n-plating/

Have you thought about checking the backlash at engine operating temperature to see if it gets smaller? Maybe heat the parts to 220-240 and check backlash again.. Just a thought..

Good thought, re: the heat issue. My guess is that everything will scale up together (the distance between the cam bore and crank bore and the diameters of the two gears). I say that because the factory spec for lash at room temp is in a range that goes all the way down to zero (.000 - .002). If the lash tightened up with engine heat, that would put gears that start at .000 (when cold) into a grindy kind of mash, no?

That's a good point. It may grow once heated since the gears are steel and the case is alum/mag.

Does your plater know how thick the nickel will be applied and can they put on however thick you want?

They claim " tolerances of +/- .00005” (50 micro inches)" on their website: http://www.accurateprecisionplating.com ... l-plating/

On the phone, Alberto said he would give me +/- .0001, which sounds more plausible, and plenty precise. I was a little unsure how much thickness to add to the surface to take up a given amount of lash, given that the teeth mesh at an angle. (I figure there's a cosine involved. Eh.) So I went conservative, not wanting to end up tighter than zero. I currently have a lash of about .0045, and I asked them to add .0015 to the surface. I should get it back in about a week.

The bores will spread further apart more than the steel gears will grow with heat.

Thanks, Pile. I figured that was likely, given the factory spec.

Any insight on the angle-of-mesh issue (or whatever it is called - I mean the fact that the gear teeth are triangles, not square blocks)? I figure .0015 added to the surface on both sides of the gear teeth will take up somewhat MORE than .003 lash, but I don't low how MUCH more.

This is a great idea..
Can't know until you try, right?

Looking forward to seeing the results of this,
And how much the thickness of the plating effects your backlash.

I'd be inspecting my oil filter very carefully at first..

At the last minute I changed my order and asked for .0018 added to the surface, not my initial, more conservative .0015.

I got the cam gear back and finally got around to doing a mock assembly. The result is a bit disappointing: the lash is inconsistent through the rotation, ranging from zero to about .003. Before plating I didn't notice any variation in the lash at different points in the rotation. But I also have a hard time imagining how the plating would be deposited inconsistently, if the whole gear is sitting in a bath. Maybe the surface prep prior to plating was inconsistent? In any case, I am going to conclude that this was an expensive experiment with ambiguous results, and move on. At its loosest spots my lash is tighter than it was initially, and at its tightest spots the cam doesn't walk out of its bearings when I reverse-rotate the crank, so I can live with it.

Good on you for jumping in and going for it!

I have found most of these straight-cut gear sets to have inconsistent lash through their rotation.

Maybe the differences didn't show themselves as much when the tolerances were looser?

Bet you it will wear in..

How expensive was this experiment?

With postage back and forth, I think it came to about $160. Yes, maybe there was a slight lack of concentricity in the gear before plating but it wasn't as noticeable because percentage-wise it was a smaller factor in the lash.

I hold out some very slight hope that setting my cam end-play (it is currently zero) might improve matters. (I know, I should have done that first.)

Always wondered if you might get a bit of the end-play difference out,
By leaving the cam/gear bolts just snug and rotating thru while nudging/tapping to correct.

yeah,
The gear locates on the cam,
But you never know...