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99 tappet

Submitted by don_constable on Mon, 03/05/2010
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Heavy Twins

I have a 1961 Dominator 99. Engine was rebuilt a few years ago with new valves, guides, valve springs, all from Mick Hemmings. Bottom end was also done.

Cam followers were not checked or touched! I have done approximately 9,000 miles over about 7 years since rebuild.

Twice now over the last 1,000 or so miles, on inspection, the right inlet tappet has been very loose (14-15 thou).Fairly sure I tightened them up correctly and the adjustment was at 3 thou. Other tappets have not changed.

Submitted by warren_dagnall on Mon, 03/05/2010

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Hi

Look for rocker shaft movement as the valve starts to open, wear can occur in the shaft location holes

Ron C.

Submitted by rob_hodder on Mon, 03/05/2010

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Previously wrote:

I have a 1961 Dominator 99. Engine was rebuilt a few years ago with new valves, guides, valve springs, all from Mick Hemmings. Bottom end was also done.

Cam followers were not checked or touched! I have done approximately 9,000 miles over about 7 years since rebuild.

Twice now over the last 1,000 or so miles, on inspection, the right inlet tappet has been very loose (14-15 thou).Fairly sure I tightened them up correctly and the adjustment was at 3 thou. Other tappets have not changed.

Greetings All,

I'm a new member to the club and this is my first posting, looking forwards to getting know members. I suspect that the cams and followers are probably behaving OK. - it would be peculiar for just one lobe/follower to fail. However I would suggest maybe you look at the rocker adjuster for the problem valve, If at a previous time they've been left adjusted very loose then they can destroy the case hardening with all the bashing. Once that has gone then they will never stay in adjustment very long. Same could also be true of the ball end.

In addition it is possible that the oil feed is blocked to the rocker shaft or within it. I've seen this happen and results in lots of wear to rocker, arm, ball end and rocker adjuster, whilst all the other valves, having a good oil supply continue to stay in adjustement.Regards Rob

Submitted by don_constable on Tue, 04/05/2010

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I removed the end plate from the rocker shaft, carefully pulled it out while the valve was fully closed and could not detect any lateral movement between shaft and head. I also examined tappet and valve top, again no signs of wear.

Could not at this stage examine push rod end of rocker, push rod or follower. If problem persists (which I fear it will!) I will lift head, then barrel to examine followers ect. As the excess tappet clearance is when the lobe is not in contact, that is when the follower has no pressure on the cam, I thought wear of the cam less likely.

Submitted by warren_dagnall on Tue, 04/05/2010

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Hi,

My suggestion may not be the whole problem but how did you remove the shaft?

The shaft is interference fit to the head and requires a puller to remove.

A lever of some sort on top of rocker may show any slack. The wear will be on the inside hole.

Ron.

Submitted by warren_dagnall on Wed, 05/05/2010

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PS,

Make sure you refit the rocker shaft with flat facing inwards to centre of engine, oil way alignment.

Ron C.

Submitted by don_constable on Wed, 05/05/2010

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Hi Ron,

I made sure left inlet valve was fully open , so there was no pressure on right tappet, then pulled shaft using a bolt (as per Maintenance Manual). The shaft was a tight 'sliding' fit. All oil ways were clean.

I have just done another check for slack on the inside hole, as suggested. No movement was detected.

Submitted by warren_dagnall on Wed, 05/05/2010

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Hi.

Good news, only other idea, may be bent push rod, if you can rotate it may show up as changing tappet clearance but an intriguing problem. Sorry canât be more help.

Regards Ron C.

Submitted by phil_hannam on Sat, 22/05/2010

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Hi Don

I would be considering a coupleof possibilities here.

1) The camshaft is the problem. Sometimes, on a rebuild, the camshaft followers get mixed up and then have to bed in again on different camshaft lobes. Was the camshaft changed?

2) You have a pushrod with a loose end.

3) You have a valve going sick. Sometimes the hardening on the stem end is poor and gives way.

Submitted by don_constable on Mon, 24/05/2010

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Hi Phil,

1) The engine has done about 9000 miles since a rebuild. Camshaft was checked and seemed ok, Cam followers were not touched or examined (never thought about them!!....)

2) Could be pushrod. I plan to run the engine for a little longer andif gap opens (which I am sure it will) I will strip and examine the pushrods, followers and camshaft.

3) When engine was rebuilt, valves, springs, guides etc. were replaced with new ones supplied by Mick Hemmings. Rockers and valve tops seemed ok when visually examined through vales covers.

I feel the Pushrod, followers and cam are the prime suspects! I am hopping the cam is ok as it is the most costly and hardest to replace, but sod's law! Also I cannot see why the cam would wear at the bottom where there is no presure??

Thank you for your interest and suggestions.

Don

Submitted by don_constable on Sat, 29/05/2010

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Hi,

To those who have kindly made suggestions.

Today I took the tappet adjusting screws out of both inlet rockets and examined them very closely using a magnifying glass to aid my old eyes. The one on the 'bad' side is about 16 thou shorter (at 1.025 inch)than the other one . Also, and perhaps more relevent, the 'Bad' tip is rounded at the edge and is showing what looks like copper????.

Not yet sure what I am seeing, but it is the first real difference I have detected.

Thanks to all above for their input. I live in Perth, Western Australia, which is a bit short of Norton expertise so your help is much appreciated.

Don

 


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