Plugs and oli burn marks

[buzzer]

Twin cam big valve, Dellortos and fast road tune. I burn a bit of oil. If its been ticking over for a while andI them drive a boot it I get a cloud of smoke which then quickly clears. I am thinking oil down valve guides but not sure. The engine overhauled 2k miles ago new rings and head professionally rebuild. What is interesting is the oil or dark patches on all the plugs. All plugs look ok colour wise but have an oil burn mark just on one face not consistent with the plug orientation but probably consistent with orientation in the bore. Any ideas welcome what causes this?

Dave

[Pfreen]

How much oil do you burn?  Were the plugs run on the highway or idle?  They don't look good as is in my opinion.  What plugs are you running?

My guess is that your rings have not seated.  To check, with the plugs removed and a flashlight, you can see the top of your pistons.  If they are dry, then you can breath a little easier.  F oil is sitting on top, that's a problem.

I had to redo the build on my tc when the  Deves rings did not seat.  After 1000 miles of break in, it used about a quart every 400 miles.  It never improved and I pulled the motor, brush honed and installed QED oem style rings, and eliminated the problem.
I attached a photo of one of my plugs after the new rings eere installed and the engine was broken in.

[jbcollier]

Could be guides/valve seals but it is hard to diagnose these things "over-the-phone".  It sounds like the engine wasn't bored so get a proper leak down test to check your ring seal.  If that is good, you could change the valve seals with the head in place.

[Pfreen]

There are no valve seals on a tc unless it has been specifically machined for them.  You would need to remove the head to either install new guides or machine for stem seals.
However, a leakdown test could be useful in diagnosing the problem.

[jbcollier]

Not unusual to fit them though.

[fotsyr]

Never replace just the rings, false economy, as usually the ring lands are worn.

[BDA]

So are you saying that pistons should be replaced with the rings?

[jbcollier]

There are tolerances for everything.  Everything can wear.  You can also repair worn ring lands depending on the application.  Ring gaps are also critical.  I have also seen handed rings installed upside down.

[BDA]

The motors I’ve built have mostly been low but hard miles and that was never an issue. It hadn’t occurred to me that it would be a problem on a motor as old as ours usually get.

[buzzer]

Cheers guys, something to think about. I will look at the top of the pistons and see what they are like. I'll also monitor the oil use and I think I'll put a Gopro looking at the exhaust and see when it smokes and then think about getting a leakdown test done. Unless there's a disaster I wont be pulling the engine just yet anyhow as have another project taking up the space.

Dave

[buzzer]

The plugs were after a long run. I am running NGK 5's so quite a hot plug. The tops of the pistons the carbon deposits look damp, no sitting oil.