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View Full Version : Chain sprocket alignment limits?



Timleech
07-08-2009, 09:55 AM
What are reasonable limits for chain sprocket (planar?)alignment,assuming all axes are parallel? The 'book' that I have just says to check with a straight edge against the faces but doesn't suggest any limits.
This particular case is a duplex timing chain, running at a fairly modest speed, but there's about 2mm misalignment over a 6" 'free' length of chain. That to me is clearly bad, but how much better does it need to be?

Thanks
Tim

Malc-Y
07-08-2009, 11:26 AM
What are reasonable limits for chain sprocket (planar?)alignment,assuming all axes are parallel? The 'book' that I have just says to check with a straight edge against the faces but doesn't suggest any limits.
This particular case is a duplex timing chain, running at a fairly modest speed, but there's about 2mm misalignment over a 6" 'free' length of chain. That to me is clearly bad, but how much better does it need to be?

Thanks
Tim

Interesting mix of metric and Imperial measurements there! :D I'm still working in Imperial so what is 2mm??
Seriously though, I think if it says align the two sprockets with a straightedge then it means just that. 2mm might not make any difference over 6' but it seems a lot over 6".

Malc. :cool:

oldtiffie
07-08-2009, 11:33 AM
2 mm is near enough to 0.080"

Timleech
07-08-2009, 11:35 AM
It's an old engine which has clearly been assembled from bits of others without too much thought. The crankshaft sprocket position is determined from the crankcase, the camshaft sprockets and tensioner are mounted in the timing case which has obviously come from another engine, these things must originally have been individually fitted. It's been run that way for several years, it's only when I came to reassemble it that I discovered why the chain was so slack! I'm now making some spacers for the camshaft end bearings.


I was using a metric depth mic to check the relationships, and a 12" rule from a combination set as a straight edge ;)

Tim

oldtiffie
07-08-2009, 12:06 PM
A truly ecumenical shop Tim.

A Mick mike prodding a prod rule??

Jeez, you'll have the Pope and Ian Paisley as kissin' cuzzins yet!!

http://en.wikipedia.org/wiki/Ecumenical

I can see me being in chains yet!! I will let you know the technical details.

Carld
07-08-2009, 02:05 PM
The closer in line you can get them will make the chain last longer.

Fasttrack
07-08-2009, 02:27 PM
Yes - what Carld said. I think it depends upon what you mean by "reasonable" limits. There is a hard limit, where once you exceed that the chain gets thrown. Below that, the closer in line the sprockets are, the less abuse the chain faces.

Part of it depends upon the type of chain and sprocket. For instance, running a #41 sprocket (those thin ones from a bicycle) in standard #40 chain will allow alot of misalignment without throwing the chain. This will still wear the chain faster than if you had them perfectly in line since the sprockets will be applying a "twist" on the bushings of the chain.

RPease
07-08-2009, 02:40 PM
That 2mm over 6" is only about 3/4 of a degree angle misalignment. I wouldn't think that would be much of a problem for a chain............but I've been wrong before.

My $0.02 worth............Rodg :D

Timleech
07-08-2009, 03:52 PM
Sorted now, all being well. After measuring again, the misalignment was in the region of 1.8mm. I was thinking in terms of making some shims for the camshaft end bearings from sheet steel, I usually have something about the place which would have done but couldn't find a thing so bit the bullet and machined some spacing washers. The end bearings have a fixing flange, 4" OD & 2.625 ID with 3 screws, I made up a pair of washers from some 4" CI bar that I had & finished them off after parting with 10 mins on the surface grinder. Another smaller spacer for the tensioner & it's all spot on now.

Before I took the timing gear apart the chain was really seriously slack but with no terribly obvious cause, the engine had probably not run huge numbers of hours since it was last stripped, but I'm happy now that I've found the likely cause and fixed it.

Tim