[footjoy]

I pulled a head off of my 400 today getting ready for changes. I checked the deck height it is .018 the gasket was a victor .045. But to my amazement this 2000 mile engine is carboned up bad. It didn't u8se oil it didn't blow smoke and the plugs were white.

Where should I start looking?

Greg

[JLMounce]

Pictures of the carboned up parts would be helpful. Piston tops? Combustion chambers? Back of valves?

Your quench distance could be a contributing factor. At .063" quench distance you're definitely not in the ideal territory. Current theory suggests this slows down the combustion process, may inhibit complete burn and actually increase the tendency for detonation.

Pics of the spark plugs may be helpful as well, but they'll only really read the last engine state, what is occurring during run operation may be different than what is occurring during idle operation etc.

I think the first thing you've got to address is that quench distance. Without taking apart the engine and decking the block or choosing different rotating assembly parts, you can't do anything about how far those pistons are in the hole. You can go to a thinner head gasket however. At about 100 bucks they're a bit pricey as far as gaskets are concerned, but I'd choose the 4.2 bore, .027" crush cometic gasket. That's going to get your quench distance at a happier .045". My understanding is this is a bit on the higher side of ideal, but it's in the ball-park and as long as you don't push the envelope on compression, should be a-okay.

Do you plan on CC'ing your current heads to determine their actual combustion chamber size?

[footjoy]

Originally Posted by JLMounce

Pictures of the carboned up parts would be helpful. Piston tops? Combustion chambers? Back of valves?

Your quench distance could be a contributing factor. At .063" quench distance you're definitely not in the ideal territory. Current theory suggests this slows down the combustion process, may inhibit complete burn and actually increase the tendency for detonation.

Pics of the spark plugs may be helpful as well, but they'll only really read the last engine state, what is occurring during run operation may be different than what is occurring during idle operation etc.

I think the first thing you've got to address is that quench distance. Without taking apart the engine and decking the block or choosing different rotating assembly parts, you can't do anything about how far those pistons are in the hole. You can go to a thinner head gasket however. At about 100 bucks they're a bit pricey as far as gaskets are concerned, but I'd choose the 4.2 bore, .027" crush cometic gasket. That's going to get your quench distance at a happier .045". My understanding is this is a bit on the higher side of ideal, but it's in the ball-park and as long as you don't push the envelope on compression, should be a-okay.

Do you plan on CC'ing your current heads to determine their actual combustion chamber size?

The pistons are totally carboned up. I am going to have the heads ccd right now if they are stock 87cc heads it figures 8.7:1 I was going to change cams and shave the heads 030 to get low to mid 9s




Thanks
Greg

[scott70]

,018 isnt horrible. I would use the reccomended .027 cometic gasket for a decent quench.

[AG]

Oil by the rings or carb mis-calibration or both. And maybe mix in some crappy ignition or some valve guide leakage.

[Half-Inch Stud]

ahem,

Carbon on Slug faces & chamber; most says "running rich", some say periods of running lean with periods of rich running because rich running washes some of the slug area completely clean leaving a carbon zone.

I say REVERSION due to exhaust reflection causes the carbon ash exhaust to reverse into CYL & Intake track during overlap. Then candle making ocurs..

So for rich or lean, for advanced or retarded, the exhaust piping is allowing an early combustion reflection to re-enter the CYLs during overlap. Idle through ~3000 rpm is the gorrilla, whereas after 3000 rpm it takes a severe exhaust problem to show reversion.

This assumes all intake valve umbrella seals are indeed down on the valveguides. Check these seals by looking through EACH Spring stack. If all8 umbrellas are in place, then research REVERSION.

[tom s]

2000 miles over how many month of driving?Mostly short trips making for a lot of cold starts?Tom

[footjoy]

Originally Posted by tom s

2000 miles over how many month of driving?Mostly short trips making for a lot of cold starts?Tom

2 years of hiway and city driving it does have overdrive and hiway driving was usually under 2500 rpm, if that makes a difference.

[Stuart]

Is it actually carboned up, or just sooty?

[footjoy]

Originally Posted by Stuart

Is it actually carboned up, or just sooty?

I would say the heads are not hard carbon but the pistons are a little crusty on the outer side.

Greg

[Boogy]

I was going to suggest you stop using that old Penzoil drum of oil, but that looked like more like thick black wax after tearing down an engine. Never mind!

[Will]

Honestly those chambers don't look terrible. Looks like you're probably running rich. Might be burning a little bit of oil - you have to be burning quite a bit to be able to see blue smoke in the exhaust.

[lust4speed]

Well, those chambers don't have any quench surface to begin with - basically an open chambered head so deck height doesn't mean anything. Running rich looks to be the main problem. Also wouldn't hurt to drive it like you stole it when you get it back together. Several pedal to the metal runs would clean most of that right up.

[steve25]

If his plugs are White then how is it you say he's running rich?

With your now confirmed .018" deck and a .045" crushed gasket things are pretty much a wash from the numbers I used when I figuered out your currrent compression of .023" for your deck and the 9.4CCs of a 1016 gasket, so if your running those heads it's still going to be mill them time and check the valve guide clearance and seal time with that carbon issue you have going on.

If the heads have not been machined for positive guide mounted valve seals then you must run valves with two grooves, one for the keepers and one for the valve stem O ring seal, and with this factory set up you need to run the metal cups shields under the retainer's

I have seen heads slapped back together with the needed O rings , but no cups and then the owner was scratching his head over carboned up plugs!

[JSchmitz]

I'd say burning some oil. Bottom chamber especially. Oil is cheap. Run the crap out of it! Might fix itself.

[HWYSTR455]

Originally Posted by lust4speed

Well, those chambers don't have any quench surface to begin with - basically an open chambered head so deck height doesn't mean anything. Running rich looks to be the main problem. Also wouldn't hurt to drive it like you stole it when you get it back together. Several pedal to the metal runs would clean most of that right up.

Exactly what I was thinking too, 1st thoughts. I would first think it's pig-rich, then maybe some ignition too.

With a lower SCR like that, it could probably take 36-38 easy, then throw 10-15 VA on it.

What carb is on this? And what's the idle vacuum?


.

[steve25]

Please post up pictures of your plugs when you get the chance.

[242177P]

IIRC, your MPG was down before. Did you ever get that straightened out?

Originally Posted by steve25

Please post up pictures of your plugs when you get the chance.

And their heat range.

[track73]

My guess, and that is what most of us are doing, would be oil
vapor coming from the PCV valve.

[footjoy]

Plugs