Loose Exhaust Push rod and Exhaust valve lifter

[Gene Nehring]

Hi guys,

I need some assistance before starting to pull the timing cover off my Series C Comet.

I was out riding with some friends and my exhaust lifter stopped working. I have ridden it home and decided I would check the exhaust valve clearance. I noticed that during a slow turn of the motor the push rod is loose at certain parts of the revloution.

I am a novice and I am wondering if the two issues are related or separate, my guess is that they would be.

I am looking for advice before I get to far into a major removal of parts.

Does anyone have any experience with this?

Thanks,

Eugene.

 

[bmetcalf]

It may be mis-adjusted. When the follower is resting on the base circle of the cam, there should be no up and down movement of the rocker, but you should be able to spin the pushrod with your fingers. If the travel of your exhaust lifter is no more that the possible mis-adjustment, it won't work. Adjust both valves and try again per the instructions in the Riders Handbook and see if the lifter works. If not, get one of those fine Vancouver Section members to take a look at things.

 

[davidd]

Eugene,

If you adjust it correctly and it loosens again on a short ride then it is probably the push rod collapsing. This happens if you have not matched the shape of the push rod end to the shape of the follower or the push rod adjuster. If the ball end of the push rod does not conform readily to the socket in the cam follower, it creates very high point loading and of course, the shape of the cams is hammering the push rods.

After a rebuild, I had a push rod that needed adjustment after every race or practice. After a few adjustments I replaced it hoping the spare would do better. It has been in the engine for several seasons now. The push rod I removed is below:

You can see that the end has collapsed compared to the stock pushrod. The best way to prevent this is by taking the high spots off the pushrod. You can do this with a stone by rocking the push rod in a dry cam follower and rocking it. When you pull it out you may see a small shiny spot on the ball end and you smooth it off on a grinding stone or diamond stone. Repeat until the entire ball is shiny and touching everywhere at the same time. Others chuck the push rod in a drill press and put fine grinding paste in the cam follower socket and run it at low speed until they match. In either case you may want to follow Bruce's advice and have a local member give you a hand with the project.

Finally, the bottom of the push rod may be digging a deeper hole in the cam follower. Less likely, but it happens.

David

 

[Gene Nehring]

Thanks for the replies guys. This is all new to me in allot of ways.

I could not explain the situation very well in words. I have done some more investigation, I removed the timing cover and found that the arm on the exhaust lifter mechanism has shawn clean off at the spring where it meets the crank case.

I am attaching a couple of photos

 

[Gene Nehring]

Here is a couple of the timing case.

 

[chankly bore]

Another reason for the valve adjustment going loose is the tappet pad ET35 not being driven right down on its registering diameter during initial assembly. it then settles under running load and, all of a sudden - loose tappet! There could be other causes, but I would get some knowledgeable aid were I you. Also, unless my ancient eyes deceive me, your steady plate and valve lifter bits look non-standard. This may not be a cause for concern but some gifted amateurs do make elementary blunders. What is the history of the machine? If you want to know how many things can be wrong with one machine do some reading on this Forum.

 

[Gene Nehring]

Your eyes do not deceive you. Upon opening the timing cover I found the non standard steady plate and a somewhat modified exhaust lifter.

I have a friend on the island who has Vincents and he may visit today.

The bike was rebuilt from a Bellingham Wa. basket case by a tool and die maker in bc and the engine was rebuilt by someone in Vancouver. I will have to call the previous owner to ask about these mysteries.

Could the failure of the lifter alone cause the loose valve? Should I be concerned about the exhaust valve condition?

 

[timetraveller]

I think that I can see why the steady plate was replaced. The clever chap has put holes in the correct places to look at the timing marks on the various gear wheels. On a Comet the plate should be steel. Is it? That, of course presupposes that the marks are still in the correct places to line up with various other things like the cam lobes. After all this time they do not necessarily do that. If the exhaust pushrod looks straight and does not have severely warn end, as illustrated by davidd then there might not be any other problem than the valve lifter. Get your chum to have a look and see in what way it has been modified. If the chap was clever enough to make a decent steady plate then perhaps he was clever enough to see a way in which the valve lifter could be improved and it might just be bad luck that it has failed. However, if the change was a bodge to save money then consider what else might have had the same treatment. Can you stand on the kick starter? If not then that suggests that valves are not seating properly and maybe the piston rings are in trouble. You can adjust the tappets to zero clearance without having the valve lifter working and check all sorts of other things without resorting to dismantling further. If that is required then be confident that a Vincent is relatively easy to work on if you have worked on other bikes of a similar vintage. Good luck.

 

[Gene Nehring]

From what I can see the steady plate does allow you to see the timing marks and looks in good order. I can stand on the kick starter, with some effort when it failed I could work the piston over TDC to kick it over to get home.

Will report back further once my friend and I have a further look.

I have allot on my plate right now, this issue I hate to say it may have to take a back seat for a bit.

I will be sure to post photos as I progress through the issue.

I have had BSA's and I still have a 1943 Norton 16H.. New machine new learning curve

 

[bmetcalf]

with some effort when it failed I could work the piston over TDC to kick it over

Some singles riders roll the bike back in gear until it hits compression, that way, when you kick it, the crank can spin a bit before hitting compression.