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t20racerman

Tr77 Front Spocket

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Hi all

 

I'm restoring a TR77 that I got as a box of bits. Attached is a photo of my old front sprocket, and the new one supplied by InMotion. The InMotion one is much wider, and if I fit it, the sprocket nut sticks off the end of the shaft and is almost touching the outer casing. The thinner older one fits perfectly. InMotion told me that they only sell the wide one for Ossas and this is the correct one.

 

Is the TR77 different to the MARs? Any ideas why this is wrong for my bike? The spacer behind the sprocket (that the oil seal runs on) is the correct 11.5mm thickness.

 

post-21505-0-96474400-1474579106_thumb.jpg

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The gold sprocket is the correct one and the raised boss faces inward. Make sure that the spacer is pushed fully home through the seal. When you first push it in it will meet resistance against the internal lip of the seal which can feel as though it has butted up against the bearing. Grease it so that it pushes through the seal easier. There should be plenty of room to get the retaining nut on if the spacer is the correct size and fitted correctly

 

MAR, TR77 and Gripper are all the same

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Hi Woody, thanks for answering :-)

 

I know that the new sprocket is the 'correct' one, but the old one was fitted originally, and this left the end of the lock nut about flush with the shaft thread. The new one means the nut only goes partly on and almost touches the outer casing.

 

I stripped the engine when I started restoring it, everything inside seems right, its shimmed up correctly and the original old sprocket fits perfectly! The inner spacer is the correct 11.5mm width AND is pressed all the way home. I'm happy to buy a thin sprocket elsewhere, or machine this one down, but I did wonder if anyone has seen this before?

 

Alternatively, what does the sprocket nut look like? How thick is it supposed to be? Maybe this is what's wrong on mine? With the new sprocket and tab washer fitted, there is about 6.5mm of thread sticking out for the nut to go on. My nut is just above 9 mm thick. (See Picture) Is this the wrong nut for the thicker sprocket?

 

Adrian

 

post-21505-0-19722800-1474655043_thumb.jpg

Edited by t20racerman

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Hi Adrian,  if you check on the Inmotion website you'll find two options for the nut. The one you have is designed for the 10T sprocket as the chain would foul the standard nut.

I can't help with the width right now as I'm working away from home, try calling them and ask them to measure the thickness. Yours does look a bit thicker than normal but that may be the close up angle of the photo.

Also the key thing with the sprocket is the chain alignment with the back sprocket. In your photo the sprocket looks very worn on the side, is the other side the same? If not it would suggest poor previous chain alignment. I'll be happy to take some measurements next weekend if you don't get it sorted before then.

Cheers, Gary

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Hi Adrian,  if you check on the Inmotion website you'll find two options for the nut. The one you have is designed for the 10T sprocket as the chain would foul the standard nut.

I can't help with the width right now as I'm working away from home, try calling them and ask them to measure the thickness. Yours does look a bit thicker than normal but that may be the close up angle of the photo.

Also the key thing with the sprocket is the chain alignment with the back sprocket. In your photo the sprocket looks very worn on the side, is the other side the same? If not it would suggest poor previous chain alignment. I'll be happy to take some measurements next weekend if you don't get it sorted before then.

Cheers, Gary

 

Thanks so much for that - I wondered why the nut was that shape! I'll not have the bike finished for at least a week or two, so measurements would be great - thanks. I'll check the sprocket wear as you suggest and see how it all lines up.

This has certainly not been an easy restoration.... :-(

 

Adrian

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If as Bondy says the raised boss goes through the seal, how did yours work ? Have you got an extra spacer in there instead ?

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If as Bondy says the raised boss goes through the seal, how did yours work ? Have you got an extra spacer in there instead ?

 

Nope, no extra spacer. I will phone InMotion, but I think the nut I have (for the 10 tooth sprocket) would have to be wider so as to enable the smaller diameter to be cleared by the chain. When tightened up its only a couple of mill proud, so its probably OK.

 

If anyone has the measurements though, please do let me know. :-)

Edited by t20racerman

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Measurements:

 

The shaft is 16mm long measuring from it's end up to the spacer inside the oil seal

 

With the sprocket with the flange fitted, there is 6mm of the shaft left visible. I don't have a nut with the flange, only a plain nut and that is 8mm thick, so it overhangs the shaft by 1 - 2mm. The flat nut is about the same thickness as the nut with the flange

 

With a flat sprocket fitted the nut sits virtually flush with the end of the shaft.

 

Early Ossas used to have flat sprockets fitted from what I can remember. I've just taken the sprocket off a MK1 MAR engine and it is flat. How this works with chain alignment between the two different sprockets I don't know as there are no other differences in the external measurements of the final drive shaft between a MK1 MAR engine through to a Gripper

 

Original gearing was 11 / 42. If you want slightly lower, as I do, try 44 on the rear and stick with the 11 tooth front as 10 can give problems with the chain, 11 is less hassle. 11 / 44 is low enough to be honest and the rear dished sprocket available these days just happens to be 44

 

 

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Measurements:

 

The shaft is 16mm long measuring from it's end up to the spacer inside the oil seal

 

With the sprocket with the flange fitted, there is 6mm of the shaft left visible. I don't have a nut with the flange, only a plain nut and that is 8mm thick, so it overhangs the shaft by 1 - 2mm. The flat nut is about the same thickness as the nut with the flange

 

With a flat sprocket fitted the nut sits virtually flush with the end of the shaft.

 

Early Ossas used to have flat sprockets fitted from what I can remember. I've just taken the sprocket off a MK1 MAR engine and it is flat. How this works with chain alignment between the two different sprockets I don't know as there are no other differences in the external measurements of the final drive shaft between a MK1 MAR engine through to a Gripper

 

Original gearing was 11 / 42. If you want slightly lower, as I do, try 44 on the rear and stick with the 11 tooth front as 10 can give problems with the chain, 11 is less hassle. 11 / 44 is low enough to be honest and the rear dished sprocket available these days just happens to be 44

 

That information is brilliant - thanks so much. Your measurements match mine - just my nut is wider than yours as it is the one for a 10 tooth sprocket. I was concerned as it just all looked 'wrong' but is actually how it should be.

 

Thanks so much

 

Adrian

 

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hi  my TR77 has the flanged front sprocket and a flat rear 42T am not sure if the front sprocket has a spacer I will have to check but the problem I had with the chain was for some reason jumping has the split link was running over the front sprocket so I turned it on the inside so the split link is on the inside. it runs ok like this but may be. The 11T would. Be. Better question can you get the tab washer on the 11T Orr dose it not have 1

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hi  my TR77 has the flanged front sprocket and a flat rear 42T am not sure if the front sprocket has a spacer I will have to check but the problem I had with the chain was for some reason jumping has the split link was running over the front sprocket so I turned it on the inside so the split link is on the inside. it runs ok like this but may be. The 11T would. Be. Better question can you get the tab washer on the 11T Orr dose it not have 1

 

Hi

 

I can get the tab washer on, but as my nut has a small flange on the inside (see picture above) there is no flat section for the tab washer to be bent down to grip on!

 

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