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Uncle_Gnome

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About Uncle_Gnome

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    Pennsylvania
  1. Uncle_Gnome

    XR75 Lower timing sprocket: Opinions wanted.

    Klxd, Thanks so much for that. Even though that is incorrect, it got me thinking and led me to figure it out for myself. By letting the crank hang by the connecting rod (TDC) it showed me that the keyway is in the 12 O'clock poition. I then drew a vertical line on a piece of cardboard and assembled both sprockets to the chain and lined everything up on the line I drew. The "O" on the top of the sprocket is positioned at a "valley". The only way that the "O" would align with the vertical line I drew was if the bottom sprocket was also positioned on the line at a "valley". No real surprise I suppose that the way it is now is the way it should be.
  2. Uncle_Gnome

    XR75 Lower timing sprocket: Opinions wanted.

    Al, Thanks for taking the time to put together that response. Mine is definitely lined up with a valley. I have two manuals and neither mention this aspect.So in a nutshell you suggest that I temporarily assemble the engine to determine how much to move the lower sprocket when it is finally replaced. Hell I just took the whole thing apart, getting pretty good at it by now. I take it that this is nothing more than a sprocket with another set of bolt holes slightly out of phase with the first. Yes the top is worn more than the lower, the lower is not truly hideously worn, but it is noticeable.Thanks again.
  3. Uncle_Gnome

    xr80 problem

    My guess is that the chain and/or sprockets are shot. Take a close look at the teeth of the sprockets and try to see if they are "hooked" sort of like an ocean wave, worn asymmetrically, more on one side than the other. Often folks try to get by with an old chain so long that you get a sort of clicking when you move the bike backward. Have you ever removed a link from the chain because it was stretched/worn? If so that would pretty much verify my theory.
  4. Uncle_Gnome

    Vintage XR timing sprocket question.

    Turboglenn, Yes it's a vertical engine, nearly identical to the 80 & 100 you worked on, especially if they were older. Realizing that I was probably in the wrong forum, I posted today in the 80-200 cc forum. Hopefully someone there has some ideas for me. Thanks to both of you for posting.
  5. Hello, I recently purchased a timing chain and upper & lower timing sprockets for my nephews 1974 XR75. The engine is really clean, with a relatively fresh top end and brand new valve job. So I think it is worth at least a little effort. My questions are regarding the lower timing sprocket. In researching the site I have learned that it needs to be pressed off/on at a shop. On this crank the key-way lines up with one of the valleys on the sprocket. In another thread however someone questioned this and said they had seen them both ways. In the past it seemed I could not get my valve timing exactly the way I though it should be. It wanted to go either too far one way or the other, as if it was out by a half tooth. How do I know that the sprocket has not slipped in the past? Which way is it supposed to go? Line up the key-way with a valley or a tooth? And lastly, assuming it is located properly, how bad does it need to be before it should be replaced? I can see some wear such as you would see on a worn drive sprocket but it is not extreme by any means. I have the crankshaft removed and the new sprocket on hand but I don't know which way to jump with this deal, have it pressed on unsure of the orientation or reassemble it as it is. Any input you guys can give me will help immensely.
  6. Uncle_Gnome

    Vintage XR timing sprocket question.

    Qwoke-q, Thanks for for the confirmation. So I take it that the teeth are fine enough that you can always get the timing "close enough" This seems rather unusual to me, having worked on autos in the past where both gears are keyed.Can anyone else add anything here?
  7. Hi folks, I am working on an old XR-75, specifically a 1974. During a previous round of work I realized that the timing chain and upper gear were showing some obvious wear. When I ordered new parts I ordered all three components, chain, cam sprocket and crank sprocket. Today I received my parts and was surprised to see that there is no key-way or any other means to secure/time the sprocket to the crankshaft. I can only assume that this part must be pressed off and on. Is this correct? Even more puzzling to me is how to properly orient/time the sprocket to the crank? I noticed before that when I timed the engine I had a hard time getting the cam sprocket to align the way I thought it should. It seemed to be either 1/2 a tooth retarded or 1/2 a tooth advanced. Is it possible that the lower gear was slightly mis-located (or slipped) all along? If anyone can shed any light on this for me I would be grateful, thanks.
  8. Uncle_Gnome

    xr 80 motor

    Slipping clutch is the most obvious thing to check. Is there enough free play in the lever? Discs shot? Norm
  9. Uncle_Gnome

    Early XR-80 upgrade

    Thanks for the offers guys, I will keep them in mind as I make my decision. Can anyone else offer me any other suggestions? Norm
  10. Uncle_Gnome

    Early XR-80 upgrade

    Hi: I find myself in need of a gas tank for an early XR-80, (1979), and would prefer to use to use a plastic tank. I have no problem performing minor modifications. Can anyone offer any suggestions? How much work would be involved in using the 85 and later tank and seat. I am sure someone must have tried this, thanks for your help. Norm
  11. Uncle_Gnome

    Problem: phillips head screws wont come out

    Pro60 I had the same problem with the same screws and finally removed them with the "Craftsman Screw Out" screw extractor set, model# 52154 and my DeWalt 18 volt cordless set on low speed. Does anyone know where to acquire replacements for this item? Norm
  12. Uncle_Gnome

    XR-75 Front end upgrade

    Hi guys I am new here having recently found this site while researching some work I am doing on an old XR-75. It’s good to see that there are still people interested in these old machines. I am in the process of reworking a 1974 model for my nephew; I have purchased a 1979 frame with the forward mounted shocks thinking that most of my old parts will transfer to the newer frame. Unfortunately I am finding out that Honda made numerous small changes that are making things a little more difficult than expected. I have located the proper airbox and have discovered that the tank and seat will not fit without modifications. My main concern at the moment however is the triple clamp. I have found that the head of the frame on the older model measures 6 1/8 while the newer frame measures 6 ¼, furthermore the stamped bracket at the top of the fork tubes appears to be slightly bent, so it seems I am in need of a new triple tree. I have seem on other posts that certain parts from an XR-100 can be interchanged with this model, (1979). Upgrading to longer travel, larger diameter forks, is appealing to me; the problem is that the boy is just big enough to ride the bike as it was. I would like to know what options I have that would allow me to upgrade now while not increasing seat height substantially until later. In other words I would like to retain the smaller 16-inch wheel for at least one more year until my nephew gains a few more inches. I have also seen references to raising the fork tubes in the triple clamp in order to lower the bike. If anyone can offer any advice, including specific year information, for this situation I would be grateful. Thanks in advance for your help. Norm
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