Consequences of High EGT's?

[myke_w]

I am trying to diagnose a failure in the head of my most recent 1.6 TD buildup. I was not running an EGT guage, but I also wasn't running a whole lot more than stock fueling (the screw was turned in 1 whole turn at most).

When driving I began to hear a "nailing" sound under load which I suspected was an injector. I took the beast into the garage and ran a can of diesel purge through it, revving it occasionally at which point it locked up, and snapped the gear off the end of the cam when it slammed to a stop.. The cam lobe snapped the shim too. A section of the vertical part of the retainer was snapped off.

The problem at hand is that one valve appears to have stuck open at which point the keepers went one way, and the valve went the other. (the valve came out as one intact piece which I found very odd.. I also noticed galling on all the exhaust valves where the guide contacts them.

Any guesses? Are these signs of high EGT's? My oil temps never went all that high (never above 130C , and I really never flogged it or even held it WOT on any long hills...

Is there a list of what fails first, second, third with high EGT's Would there be other signs that it was run too hot? The pistons look fine, no melty

Any first impressions?

I'm going to post pics later..

[addautomotive]

Since you asked...

[myke_w]

Jake, that part appears to have survived..
Perhaps I should rephrase / shorten my question..  
Are valve / guide failures directly attributable to High EGT's?

Also, I noticed that the valve seal in that cylinder is deformed... like melted maybe.. all the rest look ok tho  :?

[saurkraut]

Maybe your cam timing was off a skosh, and a valve touched the piston and bent the vavle stem.  Friction of the bent stem made the valve hang open, and got the guide hot enough to melt the seal.  closing the valve with the top of the piston eventuall did in the valve.

Just a guess...

[myke_w]

Hmm, I'm absolutely certain static timing was dead on... The motor had 1000 miles on it too.. so physical timing issues would have shown up earlier I think...

[addautomotive]

Jake, that part appears to have survived..
quote]

Look closer! The vanes ar melted right off

I would think (and I could be wrong) that your turbo would see damage before your valves would.

[myke_w]

Look closer! The vanes ar melted right off

I would think (and I could be wrong) that your turbo would see damage before your valves would.

Jake, I meant the turbo on mine survived..

I wasn't seeing a lot of smoke or anything either..

[saurkraut]

Maybe your guides were too tight.  Did you put in new guides?

[andy2]

I've had high EGT's cause valves to burn out due to tight guides.I've also seen my k24 turbine wheel melted the same as the one pictured.Stock piston to cyl wall clearance with high egt's can also cause problems.

[myke_w]

I am trying to diagnose a failure in the head of my most recent 1.6 TD buildup. I was not running an EGT guage, but I also wasn't running a whole lot more than stock fueling (the screw was turned in 1 whole turn at most).

A whole turn is MASSIVE.  Like 1/8th of a turn is a significant adjustment.  A 1/4 turn is a lot.  A 1/2 turn, you get the idea...

Andrew

Hmm, Wasn't smoking alot tho... also still makes me wonder why valve damage would predate turbo damage..
How can I be sure that I get back to stock settings on the fuel screw? Should I just back it off until the egt's are in reasonable range on a flat wot pull? Is there an offical procedure on returning a pump fuel setting to stock?

[myke_w]

Libby,
Good call.. I got the impression that you could crank it till it started smoking, then back off and you'd be ok if you took it easy..
BTW I wasn't intercooling.. That's coming in the second iteration..  

Being that I had the machine shop put new guides in, I have to still wonder if they left them a bit tight..

What would be the procedure for checking guide clearance?

The EGT bung is in the manifold now, so no more guesswork..

I'm not all bent out of shape about this, I just want to know what went wrong... I realize I may be partly to blame for the fueling thing, but I spoke with my pal who has been tuning VW diesel and gas motors alike for years and he said he's never seen a high combustion temp cause a guide to stick.

[QuickTD]

Getting back to stuck valves, my father has lots of trouble in this regard. His tractors seem to suffer worst. The cause is excessive idling. Cool combustion temps result in incomplete combustion, "wet stacking" as its usually called. The nasty tar that is formed gets into the exhaust valve guides and gums them up, the valve sticks and in his case he usually gets lucky and the pushrod just falls out... I've tried to break him of the habit of leaving things idling for hours, but he's old school...

 Not saying that excessive idling was the problem in your case, just that  valves can stick for reasons other than high EGT's. Deposits, excessively tight clearances, bent valves or nicked guides or lifter bores can cause sticking. I would think that high EGT's would be one of the less likely causes.

[myke_w]

QuickTD,
I can definitely follow your logic... keep in mind that this engine had 1000 miles on it, after a fresh rebuild with everything replaced that should have been.. new exhaust valves, new guides etc..

[saurkraut]

Did you put your valves in, or did the shop do it?  I wonder if the shop tweeked you guides a little putting them in, and the valves were too tight.

When I put new guides in, its seems that most of them go in ok and the valve slide nicely.  But typically one or two cop an attitude, and have to be reamed.  I don't have any reamers, but I have a good drill index.  I select a drill thats of the appropriate diameter using a dial caliper, and pass it through the offending guide with an electric drill.  I suspect this is not an ideal procedure, but I haven't seen any issues yet.

Did you increase the full load screw?  Its the one thats on the side of the pump next to the injector lines.  Typically, you can't get a full turn without removing the tack welded collar.  All the pumps I've futzed with, your lucky if you can get a even a quarter turn befor it bumps up against the tack welded collar.  This also raises the idle speed significally.

[myke_w]

Did you put your valves in, or did the shop do it?

The shop did my valves, they said the guide in that cylinder was worn out..
He also said that the top of the valve was beat up, as was the bottom of the lifter, and he suspected that the valve clearance was excessive, he suggested that a shim may have popped out.. The head comes from this machine shop "ready to bolt on" so I am not sure it was my responsibilty to check clearance from  the get go. I was planning to do a valve adjustment at 1000-2000 miles but we didn't get that far..

Did you increase the full load screw? Its the one thats on the side of the pump next to the injector lines. Typically, you can't get a full turn without removing the tack welded collar. All the pumps I've futzed with, your lucky if you can get a even a quarter turn befor it bumps up against the tack welded collar. This also raises the idle speed significally.

I did adjust it, but not enough to affect idle..