Replacing Valve Stem Seals (in situ) Pitfalls?

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Dan1950

Dan1950

1974 MK II Roadster
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Given the obvious signs of valve stem seal leakage and oil consumption. I think the logical first step is replacing the stem seals and see what happens.


I ordered new valve stem seals

Replacing Valve Stem Seals (in situ) Pitfalls?



As well as a rocker shaft removal tool

Replacing Valve Stem Seals (in situ) Pitfalls?



Looking for input from those that have performed this task in situ.

Specifically steps to prevent small parts from finding their way into the crankcase.

Also I have seen some home made tools to compress the spring collars in situ. I would like to see any examples of same.
 
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acadian said:
IMHO, doing it in situ will be just as much work as taking the head off, and without the added bonus of being able to check stem/guide clearances
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Couldn't agree more
How long does it take to remove the head check everything over and change the seals
And replace it?
 
acadian said:
IMHO, doing it in situ will be just as much work as taking the head off, and without the added bonus of being able to check stem/guide clearances
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baz said:
Couldn't agree more
How long does it take to remove the head check everything over and change the seals
And replace it?
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Right now there are no oil leaks and the exhaust roses stay tight.

I can check to see if valve stem clearance is obviously excessive while I'm replacing the seals. If I see anything that need further attention I'll go further.

If I pull the head, I'll want to go further.
 
Fast Eddie said:
I pulled the head to check things over after my first season of riding my Commando.

Next thing, it’s a 920 with TTI etc, etc.

Proceed with extreme caution …
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Schwany said:
What he said. Resist the temptation as long as possible.
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I just want to get the oil consumption under control with as little surgery as possible..

I spent the previous winter going through the gearbox.

Next winter I see a complete engine rebuild with a compression increase and a cam with enough overlap to ease cylinder pressure at the bottom while providing a boost at higher RPM..
 
If you have a good head seal on a Commando, do everything possible to avoid disturbing it. Every time they go on and off the stud threads in Al are begging to let go.
It's already been stated about oil level, but I'll add to it. If I run my oil level on h the bike uses a ton of oil, possibly as much as 1 qt in 300 miles.
If run at the halfway point the bike uses roughly 1 qt per 1,000 miles.
If run at L or slightly below it uses 1 qt in approximately 2000 miles.

It is a Mk 3 so there are some differences vs MK2 bikes in breather and oil tank venting.

Glen
 
My 850 mk2a always used a fair bit of oil I never measured it but it got through a fair bit ,it was mainly from the breather
This was 40 odd years ago so I can't clearly remember but I'd done away with the plastic air filter box and fitted bell mouths
I took the breather pipe up as high as I could under the tank somewhere and then down to a catch tank
This improved it a bit plus being impoverished and the bike being my only transport I used to tip the oil back in the oil tank!!
By contrast the 750 I have now barely uses any oil !!
 
There are a few older threads on this procedure. Ludwig's write up and tool cobbling guide for in situ seal replacement:

I used his homemade compressor but went with the "rope trick" method to hold the valves up, not his sparkplug hole-holder.
 

Attachments

If you remove the head, you can replace the seals without knocking out the rocker shafts. The factory spring compressor tool accommodates the rockers once you take out the adjuster.
 
elefantrider said:
If you remove the head, you can replace the seals without knocking out the rocker shafts. The factory spring compressor tool accommodates the rockers once you take out the adjuster.
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And if I remove a head that doesn't leak or let the exhaust roses come loose I might not get that same result when the head is replaced.

It amazes me that so many urged replacing the layshaft bearing in situ but insist on removing a cylinder head that has much more opportunity for a malfunction to occur.
 
Dan1950 said:
And if I remove a head that doesn't leak or let the exhaust roses come loose I might not get that same result when the head is replaced.

It amazes me that so many urged replacing the layshaft bearing in situ but insist on removing a cylinder head that has much more opportunity for a malfunction to occur.
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That's because you are comparing apples with oranges
Every part inside of the gearbox can be overhauled in situ
If you remove the head you can inspect the valve seats and valves
The general condition of the combustion chamber if it needs a decoke or not
You can check the piston crowns ,wear or scores in the bores etc
I wouldn't pull the barrel on a good running engine personally unless I were fitting a new set of rings
 
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I don’t really understand your “amazes me” comment but wish you good luck. I would just recommend you be sure you are using the right new seals for your guides.
 
In general, I agree that taking the head off is better. However, brand new build, defective seal split. Used rope and a little tool I made over 50 years ago to remove valves with a "C" clamp. Big screwdriver to lever the tool down on the springs. Whole job done in 30 minutes. Can't get everything out of the way to remove the head in 30 minutes!
 
marshg246 said:
In general, I agree that taking the head off is better. However, brand new build, defective seal split. Used rope and a little tool I made over 50 years ago to remove valves with a "C" clamp. Big screwdriver to lever the tool down on the springs. Whole job done in 30 minutes. Can't get everything out of the way to remove the head in 30 minutes!
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Why is everyone thinking that this is a brand new build when I have repeatedly cited otherwise?

My rational is that I do not want to do a rebuild at this point in time and I want to see if a quick fix can reduce oil consumption to a point where it is not a nuisance when riding this season.

Ideally, if the head comes off the cases will be split. I would not want to R&R the head for valve seal replacement only to remove it again this coming winter.
 
elefantrider said:
I don’t really understand your “amazes me” comment but wish you good luck. I would just recommend you be sure you are using the right new seals for your guides.
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See the post below.

worntorn said:
If you have a good head seal on a Commando, do everything possible to avoid disturbing it. Every time they go on and off the stud threads in Al are begging to let go.
It's already been stated about oil level, but I'll add to it. If I run my oil level on h the bike uses a ton of oil, possibly as much as 1 qt in 300 miles.
If run at the halfway point the bike uses roughly 1 qt per 1,000 miles.
If run at L or slightly below it uses 1 qt in approximately 2000 miles.



Glen
Click to expand...
 
elefantrider said:
I don’t really understand your “amazes me” comment but wish you good luck. I would just recommend you be sure you are using the right new seals for your guides.
Click to expand...
The only thing that amazes me is Norton commandos didn't even have valve guide seals for the first few years!
 
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