Measuring Lash in the idler gear

[TPXX]

To determine the amount of offset I will need in my idler bolt, what is the best way to measure the gear lash? Not being a machinist, my thought on a simple way to do it would be to use a piece of soft lead solder and roll it into the gears and then measure the thickness of the solder after it has been squeezed between the teeth of the gears. Would this work or am I way off base? If so how do you measure it?

[ronmar]

The lead would measure the gap between the gears, but backlash is a measurement of the ammount of rotation/slop in the drivetrain.  The way I measured mine was to tap a wooden wedge under the flywheel to lock the crank in place.  Before I did this, I rotated the crank so the IP cam was at it's lowest position(not pushing up on the IP plunger).  Then I removed the rocker arm assembly.  This took all the cam lobe loades off of the camshaft.  I then made up a rod that I could put on a cam gear tooth that extended outside the access hatch where it rested against a dial indicator. This is the tricky part, and a magnetic base to hold the dial indicator is really handy.  Since the dial indicator is spring loaded, once you get it positioned, the spring tension holds the rod against the gear teeth.  you want the rod end to rest on a gear tooth at the extreme edge of the camgear.  A line drawn from the center of the camshaft to the point where the rod touches should form a near 90 degree corner with the rod. and of course, the rod should extend straight off the plunger on the dial indicator.  Once this is setup, you can rock the camshaft back and forth to measure the ammount of slop the drivetrain has total. The easiest way to rock the cam is to remove the cover opposite the IP to expose that end of the cam.  Just rock the cam back and forth and read the change on the dial indicator.  By wedging rags into the gears, you can measure which relationship has more slop, crank to idler, or idler to cam gear.  This will give you an idea which direction you need to orient the offset to best compensate for the slop/backlash.

[Tom]

Most of them need about a .035 offset. That was the "standard" xyzer bolt. That and a bronze idler gear and you're good to go.

[38ac]

Lash isnt all created equal. Exacting science would  require that you know exactly where your problems lies. This means the ider would be held still and the cam and crank lashes measured seperatelly by turning them and measuring.  Although I have never tried it ( I own dial indicators)  I think you could get where you need to go with solder if you remember that the thinnest section is going to be what contol the lash. My 6/1 Metro had a terrible case of gear clatter. I put a washer under the head of the idler bolt to lock it solid and then turned the crank and cam to see where the slop was and it was by far more prevelant between the cam and idler. As a matter of fact the crank/ider lash was actualy on the tight side of perfect.

Now I am going to let a cat out of the bag on how I fixed it. I have kept this under cover because of lthe lack of operating hours for "proofing" I caution that I did this on intuition and experance only and offer it for informational purposes only.

  Lawyer talk over how did I "fix" my Metro? With a drill bit, some wax and JB Wled.  First thing I did was drill the hole for the idler bolt out bigger  Yes, bigger, one drill bit size. I then placed the idler and shaft in the block and placed a washer under the nut just over finger tight so I could tap the bolt around where I wanted it without too much force.  Once I made sure there was enough room to knock it where the lash could be made right both between the cam and the crank and then removed it and cleaned the block and bolt with brake cleaner and put two coats of hard wax on the bolt and outside of ider gear hub (D-I-Y release agent) I then timed the gears and installed the bolt and nut again with washer and just over finger tight. I knocked the idler until I got lash that suited me between both the crank and cam and tightened to nut a bit so it would not move.  I them moved the crank so it was right behind the idler gear and drove a shim between the idler gear bolt and crank to hold it. I lthen loosened the nut and removed the washer and mixed up a batch of JB and poked it in the cavity surounding the bolt until full. I then placed the washer back on the threads and the nut. Tightened it and removed the wedge and double checked the lash.. Satisfied it was OK I left it alone overnight before I started the engine. Probably 200 hours on it now and all is well. The wax should allow the bolt to be removed, if not a bit of heat will "release" the JB and just replace it with new.  Again,  although it wouldnt bother me a bit to do it on an engine I ran every day it is just not proven enough to be set out for public consumption and called a fix, at least by me. Do this at your own risk. The lash was set by past experiance with engines actualy. When it felt good I called it good. I think it was right around .002-,003 when measured afterwards.

[BruceM]

I used Ron's method of music wire and dial gauge. I ended up needing a 0.055" offset idler bolt by Dave to get the cam-idler play within reason. 

I  would try 38AC's weldbond method now that offset idler bolts aren't available, or try Quinn's offset bushing method. Weldbond would likely be my first attempt.  Thanks for sharing your new "unproven"  method, 38AC.

My suggestion is learning what your desired clearance "feels like" via the wire and dial gauge, then you can just do it by feel. It will save a lot of fussing with wire and dial gauge.  It's easiest to learn the proper feel on the idler to crank movement, then adjust the cam play by feel.

[Quinnf]

Congrats on your innovative approach to the problem.  I wouldn't have the stones to drill out that hole.  But anything you can do to eliminate the "clack-clack" sound as the cam lobes pass under the lifters will likely do the job.  I don't think high precision is vital in an engine that turns so slowly. 

I think it's been pretty well established that the excessive lash because of the improperly located idler gear pin is what did in so many idler gears.  Not the material the gear was made from, and arguably not even the presence of the "00" timing marks, though I'd have preferred to have seen some other method of marking the gear. 

Quinn

 

[38ac]

Congrats on your innovative approach to the problem.  I wouldn't have the stones to drill out that hole.  But anything you can do to eliminate the "clack-clack" sound as the cam lobes pass under the lifters will likely do the job.  I don't think high precision is vital in an engine that turns so slowly.  

I think it's been pretty well established that the excessive lash because of the improperly located idler gear pin is what did in so many idler gears.  Not the material the gear was made from, and arguably not even the presence of the "00" timing marks, though I'd have preferred to have seen some other method of marking the gear.  

Quinn

 

LOL on the "stones" but actualy it took only small ones since I do own a lathe and mill to do such things accourding to hoyle.  I could have made a bushing or bolt with any off set I wished or fixed the hole if it didnt work out.  I should caution that a person cannot drill the block out so large that the bearing section of the bolt can be drawn into the hole.  Also I could have left the block alone and modified the shank section of the bolt on the lathe to acomplish the same end but what I was trying to do was effect a decent fix that a fellow could  perform out in the middle of nowhere using tools that I would imagine any DIY type must own. So far so good, one of my problems is hours of usage lack around here.  A person who doesnt wiish to modify his block and also doesnt own a lathe could aquire a couple extra bolts and try to reduce the shanks without disturbing the bearing area I guess? I have found over the years that epoxy products when properly used are not anything less than proper fixes and I do belive that this qualifys. Time will tell.

[TPXX]

Interesting method I'm not thinking I will drill my block though! I'm working on an offset bolt, and if that does not work out, Then Ill likely go with modifying the existing bolt and getting the offset through sleeves that will be drilled off center, to match my lash adjustment. Any local machinist should be able to make me a few of those so I have some spares. Thanks for all of the information! This place is a wealth of knowledge and helpful folks!

Edited to add: Does anyone have a picture of the base, dial indicator, extension rod set up on their engine? I follow how to get the measurement, but can't picture how to "mount" everything where the dial indicator is at 90 degrees to the gear tooth. It seems that you are measuring through the access hole and the dial indicator/extension rod would not be square to the gear.

[BruceM]

True, the music wire lead-out from the idler gear will be angled perhaps 20 degrees off from the gear face, but a high precision measurement isn't really called for.  A magnetic base and articulated dial gauge holder are needed to align the dial gauge with the rod. It is a difficult measurement, and I wonder if a feeler gauge could be used instead.

[xyzer]

FWIW.....I found that trying to convert the amount of backlash to the amount of offset needed was futile! There are 2 backlash issues, the idler to cam and the idler to crank that were never the same. Through trial and error I found that 90% of the listeroids would accept a .035" offset. Some like a .040" better and I even made some .050" yours will vary. I always stayed on the conservative side that I was fairly sure would fit all of the listeroids out there. Tight is terrable! and any offset is a big improvement on any of them. The Backlash will disappear quickly towards the end..... I just made a stub shaft with a good fitting bolt diameter and machined the bearing diameter with the offset I wanted and did a trial fit. I also backed off the lifters and found a spot were the injector pump had no influence. Then make your bolt with some confidence.
good luck!

[Tom]

The offset bolt I installed was a bit tight with some gear whine. Now over 1300 hours later it's working great and perfectly quiet. Thanks for the bolt dave.

[38ac]

Just for thought and comment I would like to toss in the conversation here that the gear problems are not Indian engine exclusives. Attached is a picture of the idler out of the Lister TL (model L twin) that currently graces my shop. As you can see a bodged repair to a familar looking problem eh?  This is the second Dursley built twin I have seen with same problems, the other being a CS type. The L Lister is what the CS was based upon and the cam and idler gears are in fact interchangable.  Another item for thought is the L managed to eat it's cam drive gears without them having to drive two injection pumps, just a magneto that takes maybe 10% of the torque required to run the CS pumps. No doubt we can improve the Indian engines by getting the lash in spec but I dont think perminant can be applied, especialy to any twin.

[fabricator]

Seem like a pretty simple fix would be a variation of 38 and Quinns method, drill the block out  about  .015 and make a bushing that is off center by .030 with the OD an easy slip fit in the hole in the block, then you could just adjust the bushing till you are happy with the lash.

[xyzer]

The bushing in the block might work but it would have to be thin to assure the bolt shoulder has enough contact on the block to stay secure and not pull into the block when tightened. To get a .030" offset you would need to bore the block at least .080" and that would still be only .010" on one side of the bushing. Adjusting that thin of a bushing would be a very patient process. The offset has to be balanced as needed between both the cam and crank gear. Also be sure you rotate the assembly and check the backlash in different areas as the pitch diameter is not necessarily true to the centerline of rotation. For the DIY guys I lean towards the turn down the idler bearing on a stock bolt and silver solider an offset bushing onto the bolt. Before you silver solider locate the direction of the offset so the oil notch will be at or near the up position. Once I learned were up is I enlarged the oil reservoir just in case.

NO LONGER FOR SALE!    SORRY

[fabricator]

Any reasonably competent machine shop could make an offset bolt, especially if they have a cnc lathe.