Checking Backlash

930LDR · 07-02-2011, 06:32 PM

I'm preparing to install the oil pump, intermediate shaft and crank tomorrow. Looking ahead to the measurement of backlash I'm a little unclear on how you set up the dial indicator. My plan is to use the dial indicator from my ARP stretch gauge but can't seem to find much info on the fixture to be used to perform the measurement.

Any guidance would be much appreciated.

Thanks

Walt Fricke · 07-03-2011, 02:15 PM

I think the dearth of information may spring from the fact that backlash often isn't checked. I've never done it. May be best practices to check it every time, but - - -. We rely on the sizing of the gears, and the wear or lack of it on the aluminum gear. And if both are from the same motor, put them back in and don't worry. Nothing you can do to adjust anyway, short of getting different gears.

Porsche used to have a system where you could mix and match marked gears to get it where it should be. I think they gave up on this, and only sell one universal set? Something like that.

brads911sc · brads911sc's Garage

I think I recall reading that you can just check to make sure its slight by feel. this is what i did. and what Walt said...

304065 · 07-03-2011, 05:50 PM

You need to make a fixture out of a magnetic base and some arms. VERY hard to set up.

Jon B · 07-03-2011, 10:23 PM

It's easier to measure gear lash using a "test indicator", with a probe that swings in an arc, than an indicator which measures linear travel. Since there's very little option for adjustment, you'll have to decide what tolerance is acceptable.

One simple lash test is to lay the crank and intermediate shaft in the case, then rotate the crank in a way that will pop the i-shaft up out of its bearings if too tight (without the shaft coupled to the oil pump). The i-shaft gear should also be checked for run-out, to make sure it's seated properly.

930LDR · 07-04-2011, 06:50 AM

I ended up finding a fixture at Harbor Freight with a magnetic base ($20). Worked ok with the dial indicator from my stretch gauage. Fiddled around with it for a while until it looked as though I was getting a decent measurement as I rocked the int shaft back and forth. Looks to be approx at the 'loose' end of the range in Wayne's book.

JonT · 06-13-2018, 10:33 AM

Reviving and old thread here: Can some engine building experts confirm/refute or clarify the test Jon B suggests in post #5 for lash test:

"One simple lash test is to lay the crank and intermediate shaft in the case, then rotate the crank in a way that will pop the i-shaft up out of its bearings if too tight (without the shaft coupled to the oil pump). The i-shaft gear should also be checked for run-out, to make sure it's seated properly. "

faapgar · 06-14-2018, 05:48 PM

That is a simple test,It should be done without the seals installed under the pump.You turn the crank without rods for a rotation feeling backlash as it goes through a revolution.You also feel the connecting shaft between the intermediate shaft and oil pump that is splined on each end.Push it fore and aft as you rotate and make sure it slides back and forth freely.This indicates the shaft is straight.If you rotate the crank and the intermediate shaft moves up and down that means the aluminum gear for the intermediate shaft has an issue between two teeth.Change the gear or file the offensive area down.Simple test.Ciao Fred

faapgar · 06-14-2018, 05:51 PM

If the teeth on the aluminum gear shows any sign of pitting just change it.

Neil Harvey · 06-16-2018, 04:26 PM

Quote:

Originally Posted by JonT

Reviving and old thread here: Can some engine building experts confirm/refute or clarify the test Jon B suggests in post #5 for lash test:

"One simple lash test is to lay the crank and intermediate shaft in the case, then rotate the crank in a way that will pop the i-shaft up out of its bearings if too tight (without the shaft coupled to the oil pump). The i-shaft gear should also be checked for run-out, to make sure it's seated properly. "

Completely wrong. Do not use this method if you wish to have an accurate measurement of the gear lash. "Shade tree" building at its best.

Measure the lash with a dial indicator making sure the probe does not slide down the gear tooth. From memory, lash wants to be at least 0.002"+ on a new aluminum gear understanding that this gear will increase in size with temp and the lash will decrease. With some use this gear will show signs of wear and its important to crack check this gear too.