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ET: Engine (Twin) Tappet adjuster

Bill Thomas

Well Known and Active Website User
VOC Member
It's a common fault, It can lock the engine if bad !,
It depends what cams are used and how deep the valve seats have been cut etc.
Always pays to turn the engine over by hand with the plugs out after a rebuild or engine works.
Cheers Bill.
P.S. Well Spotted.
 

C.T

New Website User
VOC Member
Thanks bill just bought the bike it came from Belgium via yesterday s in the Netherlands to Australia it is a mint restoration that obviously has not been sorted , I have paid good money for it and I am very tentative in getting it running because the history is un known to me ,is fitted with brand new Amal m1 s which have obviously not been set up properly ,it took me a week to remove the old tank lining which I assume was put in because it was probable ment to sit in a museum smomewere ,but I intent to ride it!
 

vibrac

Well Known and Active Website User
VOC Member
Damage can be caused when caps are being taken off rather than when in use
stop if the cap is not easy to undo at that point the other one will be easy
the point of maximum interference is after a few threads are undone if the rocker is in the wrong position
 

bmetcalf

Well Known and Active Website User
VOC Member
A friend turned a bit out of the inside of my caps (carefully!) for more clearance, This would have been ~35 years ago, so I don't remember if I actually had contact or if it was just a precaution.
 

Cyborg

Well Known and Active Website User
VOC Member
Thicker seals.

Have a close look at where it is making contact inside the cap. It may be that a thinner seal (gasket) will bring the wider part of the cap down and away from the locknut. It is counter intuitive (and people think I’m not quite right which is a fair comment) but watch the motion of the rocker with the cap off. Then look inside the cap and see if the light comes on.

If the cap is fouling the rocker when you remove the cap, you can turn it back down, rotate the engine and give it another go.

Actually.... just to be clear. Are you saying they have been making contact while running at some point in the past, just with turning over the engine, or just when you go to remove the cap?
 
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Cyborg

Well Known and Active Website User
VOC Member
The not quite right guy is back...... the OP said the rocker was making contact on the inside edges (a photo would help) of the cap. “If” by that he means the narrower part of the cap where the threads are, It may be that a thinner gasket gasket (which brings the narrower part of the cap down and away from the nut) will do the job, or he may have to get some material skimmed from inside the cap. If you compare the new caps available today, to OEM, you can see a difference in that area.
It definitely helps to have this stuff right in front of you when trying to figure it out.... which I don’t at the moment, so risk of error increases.
Not to worry... if I ‘m out to lunch on this one, Robert will have me wear the pointy hat at the next gathering.
I took these back when I was assembling the Mongrel Comet engine, so going from “memory”.
First photo (apologies for the quality) is OEM, second is new reproduction. The area between the red and black marker is cut on a taper. The original is more concave in that area. Not a big difference, but every little bit helps.

57D50D78-4703-4753-8F6A-9066497E5931.jpeg4AE2171C-3C3C-46DA-A548-52548EA6C551.jpeg
 
Last edited:

Roslyn

Well Known and Active Website User
VOC Member
I know this not about tappet caps but i have different length push rods on my bike and had to take the petrol tank off to change them about to stop the tappets from rubbing is this normal any one?
 

Bill Thomas

Well Known and Active Website User
VOC Member
Yes , The last one we did, I swapped the pushrods around and the caps ,To get the best results, But still had to grind the adjusters from a spanner head to 2 flats on 2, I think, Took a long time, Every engine needs sorting
for that engine.
Cheers Bill.
 

Cyborg

Well Known and Active Website User
VOC Member
So.... after having a look at a rocker/ cylinder head/ inspection cap setup, I just want to confirm deejay449 is correct about a shorter pushrod as an alternative. My apologies. I took the liberty of editing my last post and as a peace offering submit the following.
The first photo illustrates the adjuster coming in contact with the cap. Also illustrates why rotating the engine over to somewhere close to TDC compression stroke might be advisable before removing the cap.
The second photo illustrates the difference with a thinner gasket which moves the cap down and away from the adjuster.
The third photo shows the profile of an OEM inspection cap.02AF9E3C-8248-47BD-BAF6-8748ADAE779B.jpegF7CA3DA4-F1D5-4C7D-90FB-3705489F2A32.jpeg

89D9BE69-C37B-46E7-89B4-35AA7D8DB582.jpeg
 

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