1900 ERA HELICAL GEAR SET 2

[RBPrice]

I am trying to reverse engineer some missing gears on a 1900 era antique marine engine. Two of the four gears that drive the camshaft from the crankshaft are missing. I have a cartoon of the AS-MEASURED dimensions of the crankshaft gear and the gear on the end of the Cam Shaft attached. I know the Diametral Pitch of the gears, the Pressure angle and the number of teeth for the two existing gears and the two missing gears. Both sets are 90 deg. crossed shaft arrangements. I have assumed that both mating sets were created using odd helix angles to get the center distance to be what was needed to connect the drive and achieve the 0.50 Ratio; i.e., the camshaft rotates at half engine speed. The engine is fairly large, 25 HP and is not meant to run in reverse. It was a typical trick of the old time designers to mess with the helix angle in order to get a desired Center Distance.

My gear book library gave me some formulas for finding the helix angle if one knows the Center Distance and all of the above parameters. The calculations for the 12T - 9T set on the crankshaft came very close to the existing dimensions but the calculations for the camshaft gears does not seem reasonable.

I have looked in Dudley, Jones, Buckingham, and some others but cannot seem to find what I am missing. Jones and Buckingham have the same equation.

Anyone have some suggestions?

Thanks very much

Bob Price

Bob Price
A*G*M

 

[Occupant]

I'll have to check that. My comment was solely based on the second set of 6 & 16T.

 

[RBPrice]

Hello All - I just got off the phone with the owner and he is going to send me the Cam Shaft gear for me to measure. He is also going to remove the cast housing that surrounds the Cam Shaft gear and the pinion that drives it and carefully measure the Center distance for that pair. Having that dimension to a greater certainty should help remove that variable.

He agrees we me that if he had tried to insert an 8 DP gauge into a 7 DP gear it would have been obviously too loose. And he added that the engine has been kicking around for some time before he got it without being restored probably because no one else could figure out what the missing gears were.

Stay tuned. And thanks again for all your interest in helping.

Bob Price
A*G*M

 

[RBPrice]

Hello All - an update to this saga. Seems that the owner of the engine had the wrong tooth count on the two missing gears. His initial numbers were 9 T on the lower
gear and 6 T on the upper. Actually, they are 12 T and 8 T. I got there by just playing combinations. Then we had some bad measurements to correct.

Bottom line - the gears train is as you see it on the attached sketch. There are some still some loose ends, like a good method to adjust the gears so the timing on the
engine is easily accomplished and adding a third gear to drive the magneto.

It was fun, I learned a lot and I really appreciate all the commentary and advice you folks provided.



Bob Price
A*G*M