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Old 02-18-2015, 10:10 PM   #1
earbleeder
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Default measuring crank to cam distance

What is a good way to measure crank to cam centerline distance? I need a set of metal timing gears and want to order the correct size. Old gears measured about .0015" backlash with fiber cam gear and insert crank. Since then new insert crank installed. The engine is on a stand with the crank,pistons,and rods installed. I tried it one way and got a number close to what it's supposed to be but don't want to order multiple bronze gears if I don't have to.
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Steve
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Old 02-19-2015, 12:23 AM   #2
pat in Santa Cruz
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Default Re: measuring crank to cam distance

Torque the crankshaft main caps. Don't use the OD of the cam gear flange as it is not an accurately machined surface. Just behind the cam gear threads is a 1" diameter area this is a good spot to measure across. You should be able to get a measurement between there and the crank gear press
fit diameter.
If you know someone with a GOOD micrometer, that would be the best way to measure. Subtract the radius of each shaft to get the ctr to ctr distance. On Dan Mc Eachern's gears, a rule of thumb is that for each .001 difference in center distance, the back lash will increase or decrease about .0005. If you are using Dan's gears, he will happily explain it.
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Old 02-19-2015, 11:06 AM   #3
earbleeder
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Default Re: measuring crank to cam distance

That is basically what I did except I did use the cam flange because I didn't want to chance getting a bad measurement on the threads. I used good digital venier calipers and got 4.157. The spec is 4.154-4.156. What is throwing me off is the .0015 backlash on the fiber gear. Both old gears were pretty much new/ fresh rebuild. The spec is .003-.005 with .009 being max for backlash. I am just concerned with an overly tight gear mesh because I don't think bronze will have any give. I'll try it on the thread shank and see if there's any difference.

Steve
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Old 02-19-2015, 12:59 PM   #4
pat in Santa Cruz
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Default Re: measuring crank to cam distance

I could not get a consistent measurement with calipers because fitting the jaws to both surfaces required placing them inside the timing area where it was too easy to encounter interference with the long handle of the caliper. I used a large Mitutoyo crankshaft micrometer and then confirmed those measurements when a machinist friend came by with a Browne and Sharp, both of which allowed an easy and consistent measurement from the front.
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Old 02-19-2015, 09:37 PM   #5
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Default Re: measuring crank to cam distance

Call Dan Mc Eachern. He sent me a standard size cam gear and new crank gear to install. His instructions were to fit the gears and check the backlash. If the backlash was off he would replace the standard cam gear with a properly sized gear to correct for the centerline distance being off. I was lucky and the backlash was perfect with standard gears. Dan is great to deal with.
Mike
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Old 02-19-2015, 09:51 PM   #6
earbleeder
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Default Re: measuring crank to cam distance

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Im ordering tomorrow. Thanks for the reply
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