Timing Gear Washer

[alanjd93]

Hey everybody,

I'm in the process of rebuilding my engine and while setting up the gear drive I found out I am missing the brass/bronze washer that goes between the cam gear and the thrust plate. I tried calling DSG to see if they had any spares, or at least the dimensions of it, but no such luck. Does anybody have one out that they would be able to measure? I have the ID and OD figured out, mainly just need the overall thickness. I ordered a couple oilite bronze thrust bearings from Mcmaster Carr that are close in size with the idea of cutting them down on a lathe. I'm assuming it needs to sit below flush with the mounting flange of the cam gear - the first one I machined took up all the end play in the cam and the gear was tight up against the thrust plate. I cut it down again, about 0.010-0.015" below flush, and it seems to turn smoothly - cam end play is at 0.012" which is at the high end, but still within spec. Would this be enough clearance for sufficient lubrication? Maybe I'm over thinking this... I could probably run it without the washer, but I really want to try to set this thing up how it was designed. Any help is greatly appreciated as always.

Thanks,

Alan

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[DmaxMaverick]

Straight-cut gears don't require a "thrust" bearing/bushing. They should see no lateral loading. The washer(s) are shims, for gear alignment. They only require enough gap to allow lubrication. The thickness should be what's required to align the gears and prevent excessive end-play. With the cam gear installed, you should be able to measure that gap, and adjust the washer thickness accordingly. With no mention of an allowance margin, it probably isn't that critical.

[alanjd93]

Thank you for the info! I figured it may have not been super critical, just wanted to be sure. How much would you recommend leaving for oil clearance? Currently I think I have about 0.010"

[DmaxMaverick]

That should be sufficient, maybe less would be better. It doesn't require much, and I'd be more concerned with too much. You don't want much movement at all, or the gears may not lap. All the gears are symmetric (base 16), which may be a factor.

[alanjd93]

Ok, thanks! I do have one more washer I can turn down. I just re-measured and the current clearance is actually closer to 0.015" so I'll probably go a little thicker with it this time. I'll shoot for around 0.005-0.010", hopefully that will be sufficient!

[alanjd93]

I think I figured something out. I installed a factory chain cam gear and measured the end play at 0.002"... this is significantly less than the gear drive with the first washer I made up (0.012"). Looks like I need the new washer to be at least 0.010" thicker.
I was also thinking more about the material of the washer as well... do you think the oilite bronze thrust bearings I'm using will work alright for this application? I've noticed the DSG instructions call for brass, but the kit Leroy used to sell and other gear sets from Cloyes, Comp Cams, etc tend to use bronze. I realize now it's not supposed to be an actual bearing, but this is what I got because it was closest to the correct dimensions. Thought oilite would be a plus too.

https://www.mcmaster.com/5906K414/

[DmaxMaverick]

Brass. Bronze. Essentially the same thing. "Navy Brass" is actually bronze, but that's a different application. In your case, I don't think it matters enough to change a strategy. Oilite bearings are "bronze" for a reason, and a good one. The alloy retains lubrication better and is less "hard" than brass alloy, so may be a better choice for this application, or it simply doesn't matter. The key is to prevent the gear from moving around more than is needs to. Gears and chain/sprocket are very different. I think .002" may be a bit tight, for your gear. .005" feels about right. Certainly, I could be wrong. Go back to the science of it. I'd like other opinions and experiences, but we seem to be in this conversation alone.

[Robyn]

I agree with Maverick.... .005" should be sweeeeeet.....You are going to loose a tad bit of the play when the gap fills with oil too..

[alanjd93]

Ok, I'll shoot for 0.005" for now. I don't have access to the lathe until I go back to work tomorrow. If anybody else chimes in by then I can always cut it down further or even order a couple more from Mcmaster and start over. They're cheap and easy enough to modify, plus they ship next day. If not, I'd feel comfortable running it at that clearance. I really appreciate all your help on this. I definitely have a better understanding of this setup than I did before reaching out. Thank you!

[alanjd93]

Looks like I already got another answer, thanks Robyn! Between you two I'm definitely confident with these specs. Once again, I appreciate all the input! This place has been invaluable throughout my build... especially with how much I tend to second guess myself.

[alanjd93]

Thought I'd post a final update on this...

After obliterating my last sacrificial washer on the lathe, I decided to bite the bullet and had Mcmaster make me up a custom oilite bronze thrust bearing. The pre-sized pieces I originally ordered were 1/8" thick, and by the time I got them machined down close to spec they would start cupping pretty badly (if I were trying to make a wave washer this would have worked out nicely).
This may have been due to my backyard machining skills, dull tooling, or maybe a little of both. At the end of the day I found out it's hard to re-size a washer after it's already been cut. It was a real PITA to get it true in the chuck - I'm sure there are more skilled machinists here who could have worked some black magic, but for all the frustration it caused me the made-to-order washer was worth it's weight in gold. I'm not sure if this will hold up across all brands of gear sets, but for my application it worked out nicely...

ID - 1.760"
OD - 2.435"
THIC - 0.082"

Camshaft end-play checked out at exactly 0.005" with the dial indicator.

Thanks again for everyone who contributed to this thread, it definitely saved me a lot of time and guesswork!

[More Power]

Camshaft end-play checked out at exactly 0.005" with the dial indicator.


Just an FYI: The cam is driven forward, while the engine is running, due to the force on the cam from turning the oil pump drive's spiral gear. It's the thrust plate that bolts onto the block over the front of the cam that keeps it from moving too far forward.

Where did you locate a gear drive? Scarse as hen's teeth these days. Good on you for finding one.

Jim

[trbankii]

I've had more luck with a belt sander than with a lathe when it come to reducing the thickness of a washer. ;)

[alanjd93]

I actually got it from another member in the classifieds section! It's a shame nobody makes them anymore... Although I understand for such a small market it probably wasn't too profitable of an endeavor.
Is end play measured with the cam gear installed? Only reason I ask is it seemed like there was a LOT of fore and aft movement of the cam before putting the gear on. Don't remember exactly how much, but it was well above the spec of 0.012" max. Thrust plate and shim were also installed. When I bolted the gear on it seemed to pull the cam forward and take up some of the "end play". I measured this with a dial indicator on the cam bolt head.