Long Life of a Dual Fuel Engine

[gi_jeeper]

I'm about to buy a Chevy Silverado with 135K or son on the odo. Its a dual fuel aftermarket conversion, has been driven with CNG from it was new and looks like a great deal. I was just wondering about the condition of the engine after its been run for so long on natural gas. I've heard some people comment that these engines last forever however I have also seen references to engines requiring hardened valve seats (cobalt or otherwise) to compensate for the dry properties of natural gas.

In general does anyone have advice here and do the conversions last or is a head job pending?

[larrycng]

Re: Long Life of a Dual Fuel Engine

You are correct, dry gas fuel (CNG, LPG & hydrogen) will cause accelerated valve ware. Drive the the thing until the valve start leaking.

The newer engines have a bit better valves than older engines. To extend valve life drive it on gasoline every so often (for the valve lubricant valve) and keep the engine turning slow (keep it in the higher gears).

When you have a valve job done, make sure the valve guides are tight and then go for the hard valves and seats.

good luck

Larrycng

[gi_jeeper]

Re: Long Life of a Dual Fuel Engine

What kind of mileage can you expect before this typically happens.

[Amfuel]

Re: Long Life of a Dual Fuel Engine

My understanding is GM has been phasing out the hardened valves. The good valves are only on the vin with k5 if I remember right. Rebuilds would be 100-150k without hard valves. I don't believe the CNG slapping. What, throw some abrasive soot in the cylinder to improve an engine?

[gi_jeeper]

Re: Long Life of a Dual Fuel Engine

Thats pretty interesting as this is the mileage that the gas company I'm buying from typically phases their vehicles out. I consider it a good deal if the vehicle is in decent shape but having to do an engine job ain't too good. I'll do a compression test on the cylinders to see what shape they are in. I guess that is the only way but from what you're saying I think the valve seats would need machining/reinstallation for sure. Might reconsider this deal.

[larrycng]

Re: Long Life of a Dual Fuel Engine

Why not do a cylinder leakage and find out where the leaks, if any are?

[rtry9a]

Re: Long Life of a Dual Fuel Engine

I believe the lubrication related wear occurs mostly in the softer valve guides (normally bronze inserts), not with the valve stem as implied. Some heads will accept new inserts, others have to be redrilled and retrofitted with new valves that have larger valve stems. Part of a head rebuild.

The hardened seats/valves are used to combat gas erosion from higher temperatures at the valve/head interface. I doubt the gas erosion is problem is an issue with cast iron heads, but it might be with an aluminum head or in a performance head (hot cam with lots of lift and large diameter valves) design where there is minimal metal around the valves to draw the heat away to the cooling system. Special materials are often used to fight high heat elsewhere: stainless steel, Sodium filled valves, etc.

The most efficient (bang for the buck) solution is probably a simple valve job when compressions drops. The valves are removed and dressed back to spec- takes about 15 minutes to grind. Fairly easy and cheap at a good machine shop.

[larrycng]

Re: Long Life of a Dual Fuel Engine

Just for information. One of the best things to improve valve cooling is to have the proper seat contact using a wide contact seat instead of interference valve grind. Also stem to guide is a big help, a little begger a little better. Also, when doing a valve job, watch stem height

The picture attached show valve heat transfer.

Larrycng