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#376389 05/31/11 1:20 am
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OK, I'm completely stumped by this one - and I'd really like some help, please. I'm restoring my friend's '74 Commando and just installed the cylinder head and torqued it down. I then adjusted the valve clearance as per the manual (and as I've done on mine several times before). Once the correct gap has been set and the nut tightened down, I recheck with the feeler gauge and all looks OK. Then, when I rotate the engine by hand and recheck, the right-sided inlet and exhaust are tight. I've looked inside again, and the tappet and push-rods are in the correct position. I then re-set all four and the same thing happens again! I've done this four times and it happens again. I don't have many hairs left on my head to tear out, but I feel like doing that. Any ideas?

Paul.


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Its worthwhile thinking through the things you have done or changed to determine the cause.

Without knowing this two things do come to mind however.

Firstly did you disturb the cam followers, or did you instal a higher lift cam? It is possible for the followers to bind in the tunnels if the strap that holds them is not installed correctly. Or if you have installed a higher lift cam the strap may need to be modified to get enough clearance.

Secondly, and less probable rockers. Did you do anything with them. Spacers in the correct place etc.

Im assuming the pushrods are installed correctly. It is certainly easy to get them wrong.

If you have changed the camshaft then this is very probably the trail to follow. You can also get issues with valves binding, spring clearance etc if you are lifting higher. But if they are both binding on one side then the common factor is the cam follower.

Good luck

John

Last edited by johnm; 05/31/11 2:54 am.
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Thank you, John. As I lay in bed thinking over the problem, last night, instead of sleeping, I came to the conclusion that the cam followers were sticking in the tunnel. I then read your post this morning and see that you had the same thought, so that was a bit reassuring. Thanks. The (brand new) followers were somewhat of a tight fit, but I polished them and they fit in better. I did oil them and the tunnels before installation. I think I should try to push the followers back down and wait until I can run the engine briefly, then re-check them. Hopefully, the pressure they're under while running, as well as higher oil pressure will settle them in. Is that rational or dangerous thinking?

The cam is stock, by the way. I checked the position of the pushrods many times and they are correct. The head was completely gone through and rebuilt by Baxter Cycle, so I can only assume it was done correctly.

Thanks so much for your help.


Paul

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I'm guessing the push rods are not seated correctly in the followers.

Art


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Based on what you have said then I think there is a good chance it is the followers.

I did not favour the miss seated pushrod option because this would usually show up fairly spectactularly with a loud ping when the engine was turned over by hand. It is easy to check as well by looking in the covers with a torch and backing off the tappets a little when both valves are closed and then ensuring both pushrods are free and able to rotate easily.

If you noticed the followers were tight when installed then you are probably on the right track.

Waht to do. As you say you could start the engine and allow heat and momentum to restore the followers to their correct full range of movement. And 9 times out of 10 you will probably be OK.

Personnaly I would pull the motor down and check but Im preparing race bikes and if they can possibly go wrong they will!!!!!!

My concern is that once I did instal the metal strap that goes between the followers in slightly the wrong position and the followers bound on it. This was with a hight lift cam however and it is less likely with a standard cam. I caught the problem because whenever I instal a new cam I always measure the lift carefully with a dial guage and degree disk. I saw there was an issue when the follower didn't return to the base line.

So personnally I would check. Sorry !

John

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I second johnm on pulling the pots. The followers should slide easily with thier own wieght. I know pushrod/head juggling is not much fun, but it's far better to do it now while you've got the tools out than to do it after trucking the bike home with a bent valve or worse. Peace of mind too!


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I was able to re-seat the followers fairly easily by lifting the tappets and then regain my gap. However, despite my being initially convinced that I installed everything correctly (the bevelled edge of the followers to the front, right?) I'm beginning to doubt myself. Therefore, I will heed your advice - nowt to do but yank the head and barrels.

thanks again, fellas.

Paul.


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Yes. The bevelled corner at the cam end of stock followers is front. By the way, I put red (high temp strong stuff)lokctite on the screws that hold the follower retaining plates ("straps" as posted above) and left out the safety wires. The wires made me nervous, and with the strong locktite, the screws will stay put.


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Hi, are the rocker free spinning on their spindles?
one of mine was'nt and it does the same thing.......while I am here , where do I saw that the flat followers are better for hi lift cam than the champhered ones??

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marinatlas,
Yes, without load, rockers should rock without discernible resistance and should not wiggle laterally on the spindles.
The "bevelled" corners of the followers are never in contact with the cam and are nothing to do with the lift profile. I think the bevels on the stock flat followers are to decrease the likelyhood of the follower getting hung up on the adjacent cam lobe and to provide space for oil.


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OK, so I removed the head and barrel. The tappet retaining plates were in correctly, as were the cam-followers (bevelled edge to the front. However, even with the retaining plates ("straps" as per johnm) removed, the tappets are very tight in the "tunnel".

Are there different sizes of tappets - perhaps for different years/models? If so, I may have been sent the wrong size for my friend's bike.

Paul.


Paul

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Well, right after sending the above note, I went onto Old Britts' site and saw there are, indeed, 2 sizes (standard and +.020). However, the ones I have appear to be the "standard" size. Old Britts lists the diameter of the standard as between 1.1865 and 1.1875". I'm not entirely sure what they mean by diameter, as, even together, they do not form a perfect circle in section.

I measured the new (tight) followers jutting out of the tunnel, across the barrel (not in the front-to-back diameter) and get 1.187" compared with 1.181" for the old ones. The old ones slide in and out easily. I replaced them with new ones because my friend is meticulous and he wants anything slightly abnormal replaced with new. On closer inspection (after thoroughly cleaning them) of the old ones, I do not feel any ridges on the flats but can see a line across the centre. Does anyone think I should just install the old ones? This was a non-running basket case so do not know its history.

Thanks again,

Paul.


Paul

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Paul, The old ones can be resurfaced (and should be with a new cam) and reused. You may know, but the search function on this forum takes a bit of experimentation. Note the "search tips" and using "advanced search", try "newer than 5 years". I found this https://www.britbike.com/forums/ubbt...HRASE_tappets&Search=true#Post315816 Also,
search "stellite"

Last edited by waspfarmer; 06/05/11 5:53 am. Reason: link found

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I checked the thread and it did have my warning on it but I will repeat it anyway. I rejected about 50 % of four or more old sets I checked for cracks and stellite coming off. So they need a good inspection.

Get someone with an internal caliper gauge to check the tunnel diameter and roundness. Maybe there is a strange wear pattern in there. I assume you have cleaned everything carefully and there is no rust ridge or other issue.

Try using engine blue to see where the problem is.

John

Last edited by johnm; 06/05/11 6:16 am.
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This is going to sound silly.....but what you are describing brings this to mind. I doubt your lifters are sticking, most old bikes with any miles on it will have a lot of wear in the tunnels. If you are not exactly on the back side of the lift you are possibly adjusting them on the quietening ramp. Its easy to do on a paralel twin....when the oposite valve is ALL the way down you are exactly on the back of the cam. Silly isnt it.... hope it helps you.

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Thanks, all. I inspected the tunnels carefully when I first installed the new followers and felt they were tight and they were in remarkably good shape without ridges etc. The barrel was rebored and painted by Baxter Cycle and it was in good shape.

Alan, not silly at all - I am aware of the issue with setting valves on the quieting ramp - did that with my first re-build over 30 years ago! I checked and re-checked the gaps with the opposite valve fully open. If it wasn't sticking followers I wouldn't have been able to regain the gap by lifting up the rocker arms with a screwdriver. Thanks for the thought, anyway.


Paul

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I bought a brand new set of cam followers from Norvil and they needed lapping before they'd slide through the tunnels. I used 400 grit on a glass plate and lapped each half the same number of laps until they would slide under their own weight (with oil).



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Hi Maylar

That is interesting.

I would use the engineering blue to identify the high points and then lap accordingly. I think the followers come from Andover Norton but they probably change suppliers and the quality control could be a bit hit and miss.

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Bought new from Andover last year for use with my PW3. They also needed some work to slide freely in 20,000 mile old bores (new barrels Jan 03).


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