Smoking engine and valve seals

[Sens]

Hello,

My Pagode (engine 280SL) has the problem of smoking after idle.
I read that the problem might be caused by worn valve seals.

After replacing the problem was solved!!!
for a month or two... even more smoke now...

I made a video of the stem clearance in the valve guide and that looks excessive for the exhaust valves to me.
I don't know what the clearance should we, but this is more than 0,5 mm on the diameter. Any ideas? One of the seals might have come off with this excessive clearance.

Time to take the head off and let a machine shop do a top overhaul?

Any special advise to take the head off and put it on again?
I did this before on a Volvo Amazon (sorry...) a long time ago. I think I have all the tools.


Thanks for your advise!

Halvor Sens.

[mBdrvr]

I have the same problem. I have blue smoke after the exhaust warms up.

My engine was rebuilt about 3,000 miles ago. I thought it was valve stem seals but after suggestions from this forum I did a leak down test. It indicates to me that there is a ring issue since I can hear air escaping into the head cover. I'm waiting to have it confirmed by a professional.

[Sens]

Thanks for your reaction.

It looks like your problem might be deeper in the engine.

In my case I suspect a valve seal that came loose, since it was OK for a few weeks.

Hope you can solve your problem!!

[rwmastel]

Sens,
Sorry if this hijacks your thread!

I have blue smoke after the exhaust warms up .... I did a leak down test. It indicates to me that there is a ring issue since I can hear air escaping into the head cover.

Help me understand this. I assume air pressure is introduced to a cylinder via the spark plug hole with a hose with a built in pressure gauge.  Time is measured as pressure drops from A to B.  For you, Paul, you can hear air escape UP to the head cover (or, valve cover).  Why would that indicate piston rings instead of valves?  I must be missing something, as I've never performed this test.

[Sens]

To me that is more an indication that there is a leak between the valves and the valve seats.
A compression test might confirm that.

Agree?

 

[rwmastel]

For those new to these tests, here's a nice short video discussing compression tests vs leak down tests.  I learned a little, having never done a leak down test.  I assumed it was pressure drop over time, but it seems to measure a constant pressure loss percentage as pressure continues to be applied.
https://www.motortrend.com/how-to/engine-diagnosis-leakdown-compression-test/

[rwmastel]

Sens,

Back to your question!  You replaced valve seals.  Is it normal that seals can alone be replaced and things are good?  You don't need to replace the guides at the same time?  From what I recall, guide replacement requires pulling the head off - right?  Also, do valve seats need done when replacing guides?  I don't know, just asking.

[Sens]

Sometimes replacing only the seals is a good repair, as I read, but only in 10% of the problems. Seals are cheap so I took the risk.
To change the seals you remove the springs and you can change the seals, taking care that  the valve will not drop on the cylinder.

But in my case there is so much play in the guides (did you see the Video?) that I probably have to change them as well.
And yes, that requires to pull the head off!
In that case maybe valves have to be replaced and/or seats will have to be grinded.

Quite a repair OR.... (as I read somewhere...) live with it!
However, that is not my preferred solution...

[rwmastel]

OK, thanks for the info.  Yes, I saw the video.  I hope you get it resolved and are happy for many miles of smiles.

[Sens]

Thank you!

I will keep you informed!

[ja17]

The outside of the valve guide also wears "smooth" where the valve seal grips. This along with excessive guide wear, makes it very difficult for just new seals to stay in place.

[Sens]

OK, thanks.
I read somewhere there is a new version where the seals stay better in place.

So I will take the head off and let a machine shop install new valve guides and seals, etc.

Thanks again for your comment!

Halvor