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OHC 4 stroke datsun engine timing questions

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theeoracle:
I'm having trouble trying to figure out how to time an engine i'm designing in CAD and will build. There's not much room inside the valve cover and front cover. My original thought was to use an MXL belt and pulleys but they won't work with the shaft diameter and overall OD the pulleys would be. My though right now is to use sprockets and a chain. I'm wondering is there a small low profile chain tensioner that anyone has made before. Any and all suggestions will help.

Allen Smithee:
Depends how complex you want the result to be - you could use a geared solution using two or three intermediate idler dears to keep the gear diameters down as in this wide-angle V engine:



Or alternatively use bevel gears and a vertical drive shaft like a rolls royce merlin:



AS

theeoracle:
preferably something simple but I guess i'll have to use gears for it being such a small area. There is a company in japan who created a gear driven system for a Datsun engine. I'll have to take some inspiration from that.

I'm not sure where I can get gears that would work though. The crank diameter is .5 and the timing needs to be 2:1.
I have access to 3/4/5 axis CNC machines. So I might have to make custom gears that would fit over the .5 crank shaft?

Also i'm going to have to have each gear adjustable to get rid of backlash?

Longboy:
Reducing the crankshaft diameters beyond the main bearing at the point where the MXL cogs go may work in your design. Without any reference numbers provided here nor the scale size, an example of a crank nose at .625 in. can be turned down to .312 in. to accommodate a 60/30 tooth cog set. The cog flange diameters are about 1.7 in and .95 in. for the example's cam drive case clearance needs. The alternative is a CAD rework of the cam drive area.

I just see now your post with the .5in crank diameter.

theeoracle:
So I think I can make the 60/30 pulleys work if I make the end crank diameter .375, once I bore the id some. So to attach the lower pulley I could just machine a flat in the crank and have a setscrew in the pulley like in the pic?

Also tensioning the belt is a little tricky because it has to go around the water pump passages in the front cover. I'm thinking one idler at the inspection cover in the head and a tensioner closer to the crank?

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