Valve guide replacement - all or just one?

Hi everyone. I have a 74 850 Commando. The previous owner had an anti sump valve fail in the closed position, which resulted in the engine starving for oil and seizing, only 2000 miles after a full rebuild. This was my first full summer out on the bike, and I noticed a bit of smoke from the left cylinder. The plug on the left always showed some oil fouling, so I pulled the carb to look into the port and sure enough there was quite a lot of oil in there. It is only the left intake guide that seems to be in this state, and I can only assume that the guide might have suffered from some scoring when the motor was on its way to seizing. I know the cylinders were bored out to clean them up, but I don't think any work was done to address other potential damage.

My question is this - The left intake guide is the only one presenting any problem, so do I swap ONLY it out for a new one (and potentially a new valve, depending on its condition) or do I take the opportunity to replace the lot to be on the safe side while I'm in there.

I know the wise thing would be to do everything at once, but I'm on a budget and it would be easier for me to do just the one. The other thing is that the engine was rebuilt only a couple of thousand miles before it seized, so the rest of the guides and valves should still be in pretty good condition. I'm more interested to hear any opinions out there as to whether this is a big no-no from a technical standpoint.

Let a professional head -machine shop do the inspections and decisions. :|

Trevor
It doesn't take long to change the guide and lap the valves worth a go for a few quid and two or three hours of time. It's not going to be any worse unless you balls it up, I would say give it a go if your watching your finances as for the anti wet sump valve failing ......I smell BS.
J

do your homework first on this one because 850 nortons suffer from loose valve guides also the heads crack easily if an oversize guide is not fitted properly how much is the bike smoking? does it smoke mainly when using the engine as braking? does the smoking stop if you disconnect the oil feed to the rockers? good luck with it baz

I subscribe to the if it isn't broken don't fix it camp. This damage risk by replacing out weighs the risk of not replacing just in case it will break soon.

Torontonian said:

Let a professional head -machine shop do the inspections and decisions. :|

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Have you seen some of the "pro " botch ups posted on this forum.

baz said:

do your homework first on this one because 850 nortons suffer from loose valve guides also the heads crack easily if an oversize guide is not fitted properly how much is the bike smoking? does it smoke mainly when using the engine as braking? does the smoking stop if you disconnect the oil feed to the rockers? good luck with it baz

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I would have expected homework to be done first eg VS oil seals etc.

illf8ed said:

I subscribe to the if it isn't broken don't fix it camp. This damage risk by replacing out weighs the risk of not replacing just in case it will break soon.

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It must be smoking a fair bit and oiling the plug. Whatever happened to " a stitch in time saves etc". Nothing worse than your bike smoking like a bitch, we've all had it at some point and it is an embarrassment to say the least. So I suppose the I'm to frightened to fix it excuse could work nicely!

You actually may be looking at a failed intake valve stem seal.
It happened to me right after I had the head overhauled by an experienced British bike shop.
Took a while to figure out the problem but it was a simple fix with head off bike.

I would suggest, strip, do your own inspection of all parts, then make you own decision on what you can do yourself with a single guide and tools...

If you are not comfortable take it someone you trust.....second opinion anyway...where are you?, there may be somone near you that folks a can recommend...

rx7171 said:

You actually may be looking at a failed intake valve stem seal.
It happened to me right after I had the head overhauled by an experienced British bike shop.
Took a while to figure out the problem but it was a simple fix with head off bike.

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It's not unknown for the stem seal to simply pop off the valve guide and cause these symptoms.

yes i had forgotten about the valve stem seals at least you can change them without pulling the head off ,,,,,,,,,,baz

pommie john said:

rx7171 said:

You actually may be looking at a failed intake valve stem seal.
It happened to me right after I had the head overhauled by an experienced British bike shop.
Took a while to figure out the problem but it was a simple fix with head off bike.

Click to expand...

It's not unknown for the stem seal to simply pop off the valve guide and cause these symptoms.

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Yes, but in my case the new seal was split. Maybe faulty seal or was forced on enough to split it.
After head work done and still smoking I figured problem with rings so put in new pistons and rings so when it still smoked I went back to the head.
Took a year and $ to solve but at least now the bike runs great and such low oil consumption I can't even measure it.

$pend on head. Locate trusted local machine shop preferably with experience in British motorbike machinings.

The answer to your question is simple: measure the wear in all the guides. Then decide.
If you don't have the tools or the knowledge, get the shop to measure it. And then together you decide, based on the wear tolerances.

Keep in mind, every time a guide is driven out and pounded back in, the guide bore gets chewed a bit.
And sometimes the bore gets chewed a lot, in which case oil passes between the guide and and the bore and you can start all over again.....
Stephen Hill

Update: I removed the head and the valve springs to inspect the seal, valve and guide, only to have the seal come out with the valves with a split clean through one side. Best case scenario if you ask me. A replacement is on order and it should be back together soon. Thanks to everyone for the feedback and advice.

Good. Valve seals being rubber will fail sooner or later. Re-grind valves since head is off. Copper head gasket. Clean. Copper silicone smear lightly. :|

Nice to hear simple fix.

A replacement is on order and it should be back together soon. Thanks to everyone for the feedback and advice.

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Just make sure its a good fit on the valve. I had two from a well known UK outfit and one was oversize. The engine was smoking in 500 miles. Unfortunately I couldn't recall which of my two sources supplied it but I was not happy....check everything. If it seems a bit too easy a fit on the stem don't use it. Also be careful you don't overcompress the spring and crush the top of the seal with the underside of the retainer.