Tight timing chain on a Mark 3

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Colin_McKellar

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I thought that I was being extra careful when assembling the engine from my Mark 3. When I was checking the tension on the timing chain I found it to be very tight along the top and slack on the bottom. I have moved the engine into different positions but it is tight at all times.

I removed the tensioner to see if that made any difference but it did not.

I'm sure that I counted out the correct number of rollers between the sprockets when i was assembling the gears.

Any help would be appreciated.
 
Normally the chain should alternatey be tensioned on the top and tehn the bottom as the valves are opening and closing and the valve springs either want the cam to move clockwise or counter clockwise.

Have you tried turning the engine in the opposite direction, the top of the chain should loosen off and the bottom go taut if the cam is binding in its bushes or it has no endfloat.

Its a new one for me so no doubt some better suggestions will come up shortly.
 
The engine cannot be turned the other way as it is all built up and in the frame.

I tried to check the timing tonight and it seemed to be spot on in that there were 10 rollers between what I presumed to be the timing marks.

I did try to measure what slack there is and it seemed to be about 3 to 3.5mm which is not far from the manual's 4.8mm maximum. I did have to tug the cable pretty hard to get it to move though.
 
Colin_McKellar said:
The engine cannot be turned the other way as it is all built up and in the frame.
Click to expand...

You can of course turn the engine "backwards" by engaging a gear, and turning the rear wheel backwards, and it's made easier if the spark plugs are removed first?
 
I did turn the engine backwards and the chain seemed to free off. I kept working on it by moving the engine backwards and forwards until I was happy with the tension. I nipped up the tensioner bolts and got the timing cover on.

Just when I thought things were going well one of the exhaust tappets will not free off enough to let me set the gap. Even with the adjuster out the rocker arm is still tight against the valve stem. The pushrod seems to be seated correctly too and the other 3 tappets were set with no problems.

One step forward and one step back, lol.
 
one of the exhaust tappets will not free off enough to let me set the gap.
Click to expand...


Does the pushrod move when you turn the crankshaft? When rebuilding the engine, did you have the tappets out of their bores? Were they returned to the same bore from which they came? Did you lube them and check for motion before you re-installed the barrel?
If all these precautions were taken, it is doubtful it is the tappet. The pushrods can become hung on the edge of the cup on the tappet and cause the issue you describe. Release the headbolts and try reseating the pushrod.
 
The tappet moves fine and the rocker arm was free before I put the head back on.

I did have the cam followers out to get them refaced but they were put back in the same tunnel and were well lubricated. The cup on the pushrod seems to be in the rocker arm ok and certainly moves up and down at the right time. I did try to see if I could move the pushrod but did not have any success.

Looks like I will have to slacken the head off and try and reseat the pushrod that way.
 
Read this again from Ron's post.

The pushrods can become hung on the edge of the cup on the tappet and cause the issue you describe.

You need to check the pushrod to tappet location at the base of the barrel. Been there got the T shirt :) .
 
debby said:
kommando said:
Been there got the T shirt :) .
Click to expand...

Me too. :oops: The manual says it's not possible, but I verified that it is possible.

Debby
Click to expand...

It's possible ! Could we have a show of hands from those who claim never to have done it ? :?
 
I suppose then that my hand should be slightly raised as it looks likely that the pushrod has got caught in the cam follower. I hope to get the work done over the weekend so my hand may be fully raised by Monday.
 
Of course I was speaking only on hearsay! It could never have happened to me! :oops: :roll:
 
Got the head back off last night and checked everything out. Cam followers seems to move when they are meant to, exhaust pushrods are level with the pistons at TDC but it will still not free off when the head is tightened down. More head scratching is called for!!
 
Could this happen if the exhaust and intake pushrods were accidently interchanged (them being different lengths and all)?
Or is it possible that the timing is 180 deg out of phase, and a valve is squeezing against a piston?
 
Jim. I have had the head off and checked everything. Put the head back on but haven't torqued it right up yet but now have a small gap. Will spend more time on it tomorrow and torque it all up and see if I get a clearance.
 
Torqued the head up and can just squeeze the 8 thou feeler gauge between the valve stem and the rocker arm with the adjuster fully backed off.

I'm tempted to continue and get the bike running and see if anything "pops" back into place when it is actually running. At least i know that I have something of a clearance.
 
Colin,
Are you using standard adjustors? The murshroom and ball type are significantly longer. If the valve seats have been cut a few times that's where the clearance has gone.
Best of luck,
Cash
 
Hi cash
Valve seats have not been recut and the head uses standard adjusters. All I did this time was to grind the valves in. I get good compression on both cylinders.

Am going to connect up all the oil pipes tonight and try and get some oil through the engine. I don't like turning over the engine without an oil supply going through it.
 
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