Pushrod interference

powerdoc · Oct 15, 2011

When I pulled my head today (850 mk3) on the short pushrod on the Left side was this scraped area

I put the pushrod back into the head and it seems it may be interfering with a small metal shelf that's about 1/2 way down the pushrod "port". Pic is a bit blurry but it's the shiny area above the pushrod and it seems to be in the right area to interfere.

Is this common? Am I safe to file away that shelf? (Needless to say the head will be coming apart)

pete.v · Oct 15, 2011

Pushrods may or may not turn during running. I would think that it would be marked all around unless the puchrod are not straight. Has it worn a groove ion the pushrod tunnel? I would say that it would be fine to relieve it but check the pushrod for straightness. FWIW, possibly from an earlier build.

powerdoc · Oct 15, 2011

Of course, once the head is in place it's impossible to see, but it seems to be in the right spot. I also thought about a bent pushrod. Is it easy to check? Can I just roll it on something straight or is the pushrod not cylindrical enough? Visually, not bent.

mikegray660 · Oct 15, 2011

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powerdoc · Oct 15, 2011

Does the irregular spot create a stress riser (like a bad rod) and will break there? Should it be smoothed down to lessen the stress?

mikegray660 · Oct 15, 2011

mikegray660 said:
pvisseriii said:

FWIW, possibly from an earlier build.

Click to expand...

yes most likey was not seated correctly and turned over few times and rubbed on the tunnel ( don't touch /grind it )
- if straight and caps not damaged, no problem - make sure upon reassemble pushrod correctly in place

nortriubuell · Oct 15, 2011

I had a VERY similar experience on a 1973 850 I tore down. The push rod that had the wear from rubbing on the tunnel, that lobe on the camshaft was worn down 1/4" !!! (camshaft was thus ruined :twisted: ) I read somewhere (maybe this forum, can't remember) that "some" 850s ... had not had the push rod tunnels bored out enough at the factory. Yet another example of Norton factory quality control ... or lack thereof ??? The "recommended fix" was to take the file; and remove metal from the push rod tunnel until the push rod didn't rub any more. Well, I went to work with the file and it actually worked.

Took about 5 minutes. Push rod doesn't rub inside tunnel now

Hope this helps, cheers.

powerdoc · Oct 15, 2011

Is there actually a specification for the diameter of the pushrod tunnels?

Hobot · Oct 15, 2011

Roll the p-rods against each other for true-ness. Put some ink in a band around the leevl the damage seen then drop back in tunnel and see if the shelf hits it. They don't run well and sound bad when p-rod not seated or just jams up on kicking. Scratches should be sanded smooth then polished to remove sanding evidence.

I stretch rubber bands over the rockers to hold pressure on each pushrod as its placed. I zip tie head up on bolts stuck in the spindle cover holes while diddling the pushrods and gaskets and Racers Blue Hylomar on head gaskets now for no weeps.

RennieK · Oct 15, 2011

As pvisseriii said, most likely from a previous build. I've seen a lot of rods get this damage during fitting of the head with the rod out of position. It started binding above 1st., (where you can see the 1 long scrape) then tightening the head down or turning the motor over to properly locate the rod in the rocker while out of position caused the bad damage. If the motor was ever run with that kind of contact and the rod going up and down at 3000 rpm or so it would look different.
I'd do what Hobot said and file then buff it out taking care not to go any deeper than the worst scratch. I chuck them in the drill press (taking care not to damage the ball end) and use emery tape in finer and finer grades making a long gradual indent, then on to the buffing wheel. You could use a regular drill too. If you drive hard or have a hot cam and valve springs you should just replace it.
Like Hobot said, stack all 4 rods on a flat surface and roll them along, you will see if one is out of whack.

mikegray660 · Oct 16, 2011

RennieK said:
A
I'd do what Hobot said

theres a certain mistake!

comnoz · Oct 16, 2011

That little bit of extra casting flash left in some Norton heads has been a common problem since the beginning of Norton twins. Get in there with a file or a die grinder and remove the edge where it has been rubbing. If the pushrod has a notch big enough to feel I would replace it. Jim

PS, Maybe not since the beginning of the twin but since somebody decided to go with larger diameter pushrods [Atlas?] but did not change the size of the pushrod holes in the head.

RennieK · Oct 16, 2011

I've always understood Commando pushrods were adequately robust and not considered a weak link in the valve train in stock or combat engines. Just wondering how prone they are to failure (not due to hot cams and stronger valve springs or valve float issues). I have seen some that have a flat spot on the ball end around their circumference where the contact is made. I don't know if that's an oil problem, out of adjustment problem or just age.

comnoz · Oct 16, 2011

RennieK said:
I've always understood Commando pushrods were adequately robust and not considered a weak link in the valve train in stock or combat engines. Just wondering how prone they are to failure (not due to hot cams and stronger valve springs or valve float issues). I have seen some that have a flat spot on the ball end around their circumference where the contact is made. I don't know if that's an oil problem, out of adjustment problem or just age.

I have always ended up back to stock pushrods even it my racebikes with big cams. The only failures I have seen are loose ends and if they are only slightly loose I have fixed them with JB weld.

Steel and titanium pushrods have caused problems for me such as broken rockers and lifters. I decided the little give of aluminum pushrods was not such a bad thing. Jim

RennieK · Oct 16, 2011

I have some PR's that the ball end got rusty on while the rod is in mint shape. I also have some bent or damaged rods on some others but the ball ends are perfect. How easy is it to remove the ends on the Norton rods so I can swap them around?

comnoz · Oct 16, 2011

Very easy. Chuck one end in a drill press and the other end in a small vise attached to the table. A couple small pieces of aluminum with a hole drilled between them will protect the end from damage. Then just a smart upward smack on the quill handle and you have two pieces. Heating the end will make them tighter so do it at room temp or stick them in an icebox first. Jim

RennieK · Oct 16, 2011

Thanks Jim, I'll try that. Is it safe to put a thin solid rod in the tube and tap it on the bench to get the 2nd ball end off?

I was thinking of a suitable valve spring seat (that would slip over the end) with appropriate collets to but to the ends and that attached to a slide hammer. A little beyond my capabilities at the present. Ludwig's probably already got such a tool but shipping would be too expensive to borrow it.

comnoz · Oct 16, 2011

Rennie,
I pull the second end off just like the first one. I clamp the pushrod in the vise between two pieces of aluminum with a hole drilled between them- slightly smaller than the pushrod shaft. If the tube wants to slide in the clamp you made just use a little valve lapping compound for grip. The ends come off pretty easy most of the time.

Another use for valve lapping compound. Next time you have a socket head capscrew and you think the allen is going to slip when removing a tight one- a little lappimg compound on the end of the allen works wonders. Jim

Pushrod interference

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