I just started putting a top end back together. I took it apart about two years ago. New pisrtons. .20 over bore, new valves and quides. I kept and used the original push rods. I was to the point of adjusting the valves when I ran into a problem. I adjusted the intake valves. No problem. I adjusted the left exhaust valve. No problem. The problem is with the right exhaust valve. It will only open up to about 1/2 the required clearance. All the pieces were marked during disassemly and everything went back in the proper place. All the machine work was done by a good motorcycle shop. This is the third Commando top end they have done for me. All 4 valve adjusters appear to be the same height. No work was done on the cam or the cam followers. Has anybody had a problem with valve stems being to long?
850 MK III Valve Adjustment
- Thread starter Bobs850
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That's what I'd be hoping too. Seems like I had trouble getting them in once....I think I ended up with a trick of tying the pushrods up with rubber bands into the head and then cutting them. Does that sound right on a Norton. It's probably been about 40 years.
When you say it will only open up to half the required clearance, what happens? It's hard to visualize running out of clearance, unless you are using mushroom type adjusters. There's nothing to stop you from backing off the stock adjuster till it's flush with the rockerarm. Did they cut new seats for the new valves? Maybe they went a little deep on that one valve.Bobs850 said:
When the head was redone, they installed a new style adjuster that is adjusted with an allen wrench. Each of the other three have about a tread and a half of adjustment left. You cannot untread the adjuster out of the rocker arm.
You can turn the engine by hand and all the valves appear to open and close properly. No strange noises.
It is hard to think about a poorly aligned or installed push rod. That will be something to check when the head comes back off.
I hope the only thing I am out is the head gasket and some time.
You can turn the engine by hand and all the valves appear to open and close properly. No strange noises.
It is hard to think about a poorly aligned or installed push rod. That will be something to check when the head comes back off.
I hope the only thing I am out is the head gasket and some time.
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Bobs850 said:
That does sound like a 'mushroom' adjuster?
There should be sufficient adjustment available, even with the mushroom adjusters, and if the other three can be adjusted correctly, then it sounds as if there is a problem on that valve gear assembly somewhere?
Either the pushrod hasn't fully seated (generally at the lower end) or the valve seat could have been over-cut?
The pushrod could also be the wrong length? I found one that was too long in my own Commando which wouldn't allow enough clearance with a mushroom adjuster!
I didn't think about push rod length since it all came from a running motor didn't it? That's certainly possible. I don't think I've done it on a Norton but I think on another brand when a neighbor had a non seated push rod we just loosened the adjusted, all the head nuts, and lifted the head just a bit to get clearance to re seat the push rod.
maylar
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I had a valve & guide job done this year and the machinist had to cut the seats pretty deep. He also milled the head surface flat. Both conditions contributed to poor rocker clearance, requiring me to trim the pushrods by .050.
Best case is that one pushrod is hanging on the edge of the lifter, but typically that's pretty obvious when you turn the motor over. Often you'll get a loud "CLICK" when it finally falls into place.
Best case is that one pushrod is hanging on the edge of the lifter, but typically that's pretty obvious when you turn the motor over. Often you'll get a loud "CLICK" when it finally falls into place.
If you are using mushroom adjusters, it is likely that you will have to remove some material from the underside of the rocker arm to allow the adjuster to be wound back to achieve the correct valve clearance.
If you are using lash caps as well then you will need to remove about 0.1" from the valve stem or an amount equivalent to the thickness of the lash cap to correct clearance and geometry issues.
Or if the head or cylinder has been skimmed significantly then the effectice pushrod length will be too long and hence the same effect.
You will need to reolve this before attempting to run your engine otherwise the cam and tappets will suffer.
I have had this type of problem when dealing with Tri/BSA Triples.
Rgds,
John S
If you are using lash caps as well then you will need to remove about 0.1" from the valve stem or an amount equivalent to the thickness of the lash cap to correct clearance and geometry issues.
Or if the head or cylinder has been skimmed significantly then the effectice pushrod length will be too long and hence the same effect.
You will need to reolve this before attempting to run your engine otherwise the cam and tappets will suffer.
I have had this type of problem when dealing with Tri/BSA Triples.
Rgds,
John S
I pulled the head this morning. All the pushrods were seated correctly. The head was not milled and it apperas that the two exhaust seats are cut the same. I put the old style adjusters back in and now have enough adjustment on the front right exhaust valve.
I have had the bike for about 5 years. A friend gave it to me because he was not riding it. Hed knew when he came to visit that he could always take it for a spin. He had no history on the bike. I drove it until the stripped exhaust threads became an issue. I probably should have just had the threads fixed. I would guess that changing to the mushroom adjusters brought some other issue to the forefront.
Thanks for all the input. I had never run into this beofre.
I have had the bike for about 5 years. A friend gave it to me because he was not riding it. Hed knew when he came to visit that he could always take it for a spin. He had no history on the bike. I drove it until the stripped exhaust threads became an issue. I probably should have just had the threads fixed. I would guess that changing to the mushroom adjusters brought some other issue to the forefront.
Thanks for all the input. I had never run into this beofre.
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