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Need help please - mesh of the gears too tight

Capt...John

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I got the gears on the camshaft & crank, but the mesh of the gears are to tight. How do I correct this problem. This is on a model Holt 75. Thanks, Capt,n
 

Tom Jamboretz

Subscriber
Last Subscription Date
08/04/2019
Re: Need help please

There is a chance eccentric bushings for the cam could be made. It will allow you to rotate the bushings till proper clearance is achieved. I've done this on single cylinder engines before with good results. TJ
 

Thaumaturge

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68
Last Subscription Date
07/12/2019
Re: Need help please

Can you lap them in with clover compound? Works on tight threads.
Doc
 

Capt...John

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Re: Need help please

Tom, would this mean that I move the hole in the bushing about .002 off center? How would you do this? Machine the bushing in my lathe then place in vertical mill & do the .250 Dia hole for the cam shaft in mill? I do not have a 4 jaw chuck to off-set the hole for the camshaft. Thanks John
 

Thaumaturge

In Memory Of
Age
68
Last Subscription Date
07/12/2019
Re: Need help please

You can turn an offset bushing in a three jaw by shimming on one or two jaws.
Doc
 

JasonB

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Re: Need help please

Is it possible to bore out the existing holes in the case a few thou oversize but in the correct position and then just make up some oversize bushes.

I always prefer to have the gears to hand and then use them to actually establish the ctr distance with a slip of thin paper between the gears to give a little backlash. This is how I would work out where the new holes needs to ge bored.
 

FredsSleds

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Last Subscription Date
12/13/2019
Re: Need help please

If the gears have part numbers on them contact via the internet the information on the gears, you will find the pitch diameter and between both gears adding the radius of the pitch diameter of each gear will give you the exact dimension of the gear locating holes. The boring out the holes you have now and re drilling is probably the best repair. (just my 2 cents)
 

Capt...John

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Re: Need help please

I made a "test" bushing by shimming 2 jaws of the 3 jaw chuck. Shim was .003. I got to rotate the bushing too see if it helps. So far about the same....I will check more.
 

Andrew Mackey

Moderator
Last Subscription Date
05/14/2017
Are the gear teeth bottoming on the hubs or are the faces of the teeth binding against each other? If they are bottoming, a slight dressing of the gear tips, with a jewelers file may help. If the gear teeth are binding against one another either offset the bushings as noted or re-profile the gears to mesh properly. If you offset the cam too much, it will affect how the lobes contact the livters, which may change the timing a bit.
 

Capt...John

Registered
Well the .003 shim in the chuck to get a off-set did not seem to work. I do not know how far a .003 shim would create a .003 of-set. Probably not...it may take a lot thicker shim????

I did measure from outside surface of cam & crank. It is about 1.112 inch apart. I figure it should be 1.125. in between shafts. It sure does not look .013 too close. 1/2 Crank = .250 dia 1/2cam= .125 dia. .125 + .250 is .375. Minus the .375 I gives 1.125...... centers should be 1.500 apart too print. Does these figures seem right...I still an getting over the flu & may be way off on my figures. :(:bonk:

---------- Post added at 03:42 PM ---------- Previous post was at 02:59 PM ----------

Are the gear teeth bottoming on the hubs or are the faces of the teeth binding against each other? If they are bottoming, a slight dressing of the gear tips, with a jewelers file may help. If the gear teeth are binding against one another either offset the bushings as noted or re-profile the gears to mesh properly. If you offset the cam too much, it will affect how the lobes contact the livters, which may change the timing a bit.
I would say the teeth may be binding against each other ....there appears to be a small clearance between the end of each tooth. How would a person re-profile a gear tooth...many really!
 

Tony Rye

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Last Subscription Date
08/24/2018
can you get off set main bearing are shim them down a lot of the older diesel when we had to line bore you had to move the crank back down
 

Capt...John

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Can the gears be re-done on a gear Hob ? I know a guy that has one...he will be back in a few days. Thanks ....keep the Ideas coming....it all helps. Capt,n
 

FredsSleds

Subscriber
Last Subscription Date
12/13/2019
Can the gears be re-done on a gear Hob ? I know a guy that has one...he will be back in a few days. Thanks ....keep the Ideas coming....it all helps. Capt,n
If your going to go this far as to have them recut, just make new blanks the correct diameter and cut them?
 

Manorfarmdenton

Registered
For what its worth I'd run the gears on my vertical mill, one fixed on a stub in the collet and the other free to rotate on a stub in the rotary table, and see if they'll run in with grinding paste. Its got to be worth a try before you do anything more drastic? You could gradually bring them together while they were running to see if you could get to the correct centres.
 

Matthew Guy Clarke

Subscriber
Last Subscription Date
09/23/2019
I am not sure now with out researching how it looks, which way the cam sets from the crank, but to find how much of a crunch you have, I would suggest to start, place some shim stock around the crank for lift away from the driven gear until you estimate how much of a problem you have in thousandths. Then you could set one gear up on a dividing head, and recut it, first maybe turn it smaller. You may even be able to turn off .010 and use a file and make the depth greater.
Bob Manskee use to make his gears on his lathe, he would tell people that when they would ask where he gets his gears, and they would walk away scratching their heads. What he did was grind a tool cutter the shape of a gear tooth, then he would use the pin holes on his old Atlas lathe, which of course was numbered a correct division, and then he ran his bit back and forth screwing in the lead screw till he had his depth.

It may make some one mad to mention it, but on UTube,they last thing I looked at before reading this post was one of the Holt models running has a terrible winding sound I attributed to the C-C distance being off a bit, RRRrrrRRRrrrRRRrrr. How frustrating I am sure.
 

Tom Jamboretz

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Last Subscription Date
08/04/2019
Capt.' I'm talking about a sizeable off set hole in the bush. Like .020". When it is assembled you can rotate it till you have the clearance required. If bush is made with a hex or square end it can easily be rotated. PM me if you need more info on this procedure. TJ
 

Capt...John

Registered
I really like the Ideas all you guys have posted. I think I will try another off-set bushing first. May use that Idea & run the gears in my mill to polish the mating gear teeth for smoother fit of teeth. I wish I had went with my first Idea of using a mini timing belt & matching hubs for the belt to run on. Also I could have had a idler pulley to tighten the belt???? Thanks again for your time you took for replies. Capt,n :uhoh:
 

Matthew Guy Clarke

Subscriber
Last Subscription Date
09/23/2019
I can not recall how the Holt looks, can you determine a C-C some how. Maybe you could make shafts to fit both cam bearings and crank mains and determine exact measurement distance and check plans and know how far, too close you are. I have a Henry Ford book and could cipher the correct distance. I have made enough gears to know it can not be maybe .002-.003 ?
When I drill cam holes I set the block on the mill, aligning centers and drill - bore one then move the table say .875 and have not had too much trouble.
 

b7100

Subscriber
Last Subscription Date
07/10/2019
I just learned how to cut my own gears. It took a long time to figure it out but after I got it figured out it wasn't that hard. It has opened up a whole new capability for my shop. The projects I can see down the road with this capability are endless. It wouldn't be hard to take one of your gears as as pattern and make a new one at a smaller diameter or possibly recut the one you have if you could measure the distance you have center to center. Lapping compound might work if they aren't too far off.
 
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