Chewed Up Idler

[akghound]

Oh NOOO!!    I lost another idler gear in my engine; this is the second one. The engine seemed to running just fine, no indication that there was trouble brewing, then bam, it was suddenly out of time, then dead.  The good part is there seems to be no damage to the cam gear. I actually didn't pull it out yet, just looking from the outside.
At any rate this is a 16/1 Saytajeet (GM90) and I would like to find out if there is a brass or bronze gear available for it. Other then a small inverter and old weak batteries this is our only source of power so it is imperative that we get her going ASAP.
In fact any ideas or opinions are helpful and welcome.
Thanks, You guys rock!!
Ken Gardner

[sawmiller]

Hi Ken

Sorry to hear about the idler i'm on my second idler myself.  They are both brass .I don't think it a gear problem ,i think it's the way they set up.  There are people working on the problem . they are working on an offset pinion shaft.

Regards
Tim

[Geno]

George may have some some in bronze.  http://www.utterpower.com/idler.htm  Others may have cast.
This has become a real problem and not just on twins anymore. To the best of my knowledge its only the higher hp singles that break gears aside from the occasional 6/1 with stamped timing marks.
See this post  http://listerengine.com/smf/index.php?topic=231.0

Is this the difinitive procedure for measuring backlash? How about .005? Checking every 45º or so of rotation would indicate if the idler is out of round. Mine will be going back together soon and I want to make sure its right.

Quote from: Tom on May 24, 2006, 10:18:56 pm
Guy and Kevin,

Just to confirm that we are all talking the same thing. The lash would be measured with a dial indicator on a tooth of the cam gear and the measurement would be the amount of rotation before the slop is taken up in the gear train. And if that is the case Guy's number of 5 thou would probably be an undetectable amount when just rocking the gears back and forth.

It seems like excessive lash could be contributing to the gear failure some have experienced as the gears slap against each other. It seems like I need to attend to this before I have "chunks". And seeing as Tim lost a bronze gear that is not the answer either. So what should I do? Put the aluminum one in that I have on the shelf and see how it fits?

Tom

Thanks, Geno

[Andre Blanchard]

they are working on an offset pinion shaft.

Regards
Tim

That sounds like it fits in the category of (If you can't make it right make it adjustable.).

[xyzer]

I know this issue has been discussed before but could you give a brief description of the typical idler gear failure and the condition of the remaining teeth if any. Thanks!
Dave

[Doug]

Chain drives would be nice eh?

Doug

[mobile_bob]

how are the gears failing?

are teeth breaking off? or..

is the gear cracking in half or what?

perhaps there is a problem with the heat treat on the cast gears?

would like to hear how these are failing, i have a 25/2 ashwameh that i intend on putting into service
and Joel provided me with a bronze gear, but i would like to know what is happening to the gears

bob g

[xyzer]

how are the gears failing?

are teeth breaking off? or..

is the gear cracking in half or what?

perhaps there is a problem with the heat treat on the cast gears?

would like to hear how these are failing, i have a 25/2 ashwameh that i intend on putting into service
and Joel provided me with a bronze gear, but i would like to know what is happening to the gears

bob g

Also are the teeth wearing thin then failing?

[fattywagonman]

Hi Ken... Too bad about the gears... They seem to be a common point of failure on these engines.... My solution would be to replace the timing gears with a cog belt drive... to do this I would relace the cam shaft with a longer one and extend it out through the cover that the injector pump connects to... Insted of pins just braze the cam lobes to the new shaft Then remove the flywheel and install a coged type pulley on the crank... and replace the flywheel..  Fasten another to the extended cam shaft and make an idler / tensioner  in beween.. A good quality belt should last for many years...   I know this is more work than most folks will want to tackle.. but after it's done I think you would have a better engine... 

[JohnF13]

I have some bronze idlers here, if you need one in a hurry I can UPS one down to you tomorrow morning.  That is, assuming the GM90 gears are the same as all the others.

John F.

[listeroidsusa]

The timing gears and idler for the 14/1 and 16/1 GM-90 are the same as the standard 6/1 and 8/1 CS. I'll check my shelf in the morning and see what I have in stock. If I were to tool up my gear hobber would anyone be interested in steel gears with either needle bearings, ball bearings or bronze sleeve bearings for the idler pinion? I'll check and see if I have a hob of the correct pitch and pressure angle tomorrow. Once I set it up I can cut at least 6 at a time. Another option is to make them from ductile iron billet, or semi-steel, which is much more shock resistant than the cast iron of the originals.

I have a Brown & Sharpe gear tooth vernier. I'll check the working depth, circular pitch,addendum,  dedendum,  Pressure Angle, and Diametral Pitch tomorrow and see how they compare to a standard US made gear.

A run of offset pinion studs is also possible if it is determined that the problem is the backlash. The problem I see with the offset pinion is that it is not always possible to split the difference between the two gears. You could set one gear right on the spot with an offset but not necessarily the other gear. I personally feel that a gear made of stronger material is the best solution. Helical gears with a small angle would be the strongest and quietest solution but would be expensive and more difficult to implement. A small angle, just enough to ensure continuous mesh, would run quiet and with minimal side thrust.

Just a few thoughts,
Mike

[Halfnuts]

I vote for roller chain and sprockets.  That would last forever in there.  A spring-loaded tensioner would compensate for wear and if one were really motivated, a gear pump from a car could be used to pump oil better than the reciprocating pump on some of the roids.  It'd be self-priming, too.

halfnuts

[GuyFawkes]

I vote for roller chain and sprockets.  That would last forever in there.  A spring-loaded tensioner would compensate for wear and if one were really motivated, a gear pump from a car could be used to pump oil better than the reciprocating pump on some of the roids.  It'd be self-priming, too.

halfnuts

If I had a listeroid by definition I would not know precisely what was different from lister, given that unknown I 100% agree that any shop time invested would be on a solution that I could guarantee 100% effective and reliable, and that would be duplex or triplex roller chain, it's a tried and proven technology that will last many many thousands of hours and be cheap and easy to replace when it eventually wears out, unlikely to be within 10,000 hours.

[listeroidsusa]

Chain drive sounds very doable to me, and might be the best solution for the long haul. The chain could easily be tensioned with an offset pinion and locked in place. I think this is an idea that deserves further investigation. The crank gears are steel and the idler and cam gear is cast iron. In automotive practice the crank gear is steel mainly for wear due to the fact that the teeth are in mesh twice as much as the cam gear. The fact that the camshaft is not evenly loaded also may contribute to the gear's failures at a specific place. Multi-cylinder engines have much more evenly loaded cam drive trains. The injector cam also contributes its pulse to the gear train. All in all, the chain and sprocket setup looks good. The main task is to remove the crank sprocket and either place a pin or mill a keyway to prevent rotation of the sprocket. Either will create a stress riser. Perhaps a shrink fit would work better? The cam gear also presents its difficulties with the transfer of the governor system to a sprocket. Possibly the cam gear could be turned off of the cam/governor assembly on a lathe to the required clearance  and bolted to the remainder of the cam/ governor assembly. I'll look into the feasibility of this tomorrow also.

Mike

[Halfnuts]

Yes.  Make it so.

Halfnuts