Carbon Buildup and Stuck Valves
 

Greetings, I'm a newbie here so be patient with me. We own a 1949 Flxible bus with a GMC 401. I posted photos awhile ago. The bus has been sitting for 25 ++ years in a barn and was stuck when we bought it a few months ago, We just tried to make our 1st trip- approx 450 mile to the FLX rally in Loudonville OH this past weekend. In Venna WV, we stopped to spend the night. The next morning the bus had a dead miss. LONG story but i was able to determine i had a stuck intake valve on number 1 cyl.
When we pulled the head the engine was VERY clean except for the intake chambers? I had to drive the valve out of the head but after we cleaned the valve guide and and valve stem they where fine. No warp, no wear. So, what caused this? We completely cleaned the head and made it home using the old gaskets and such. Now i realize several things- the timing was to high, the valve where adj. to tight, the points where a little off, but was this enough to cause excesive carbon? We are now running Marvel mystery oil in the tank and crankcase as well as lead additive in the gas. I am going to need head gaskets at some point i guess just because i reused them. Help me here- what are your thoughts? Thanks in advance for your input.

ja

Re: Carbon Buildup and Stuck Valves
 

Could be pulling oil in the pcv system. But a stuck valve on a running engine. Carbon would not do that. . So a rig that has set 25 years. How well did you clean the fuel system? A black tar residue could be in a poorly cleaned tank. That will dissolve into the fuel. And it will stick valves like crazy. And if it had copper head gaskets. Use those wuth no worries.

Re: Carbon Buildup and Stuck Valves
 

Thanks for your reply. I drained both fuel tanks of approx 40 gals of very stale old fuel before we attempted to start the bus. I did not flush the tanks. It has 3 fuel filters, all have been changed. We have prob run approx. 100 gallons + thru it at this point. Both taks are full at this time but if you feel it best that i drain and clean them , i will.

I have not noted any oil in the PVC filter element. I have not replaced it but do have one on order. This engine looks brand new inside- absolutely NO internal wear. The inside of the intake chambers where the only thing that looked bad. I will attempt to attach a photo.

We know the complete history of this bus and feel certain the engine has less than 20,000 miles.

I appreciate the input! Jerry

Re: Carbon Buildup and Stuck Valves
 

I just added an additional photo in my album of the cyl head removed and the valve that was stuck, removed. You can see the build-up in the chamber. This photo also shows how clean this engine was at disassembly. ja

Re: Carbon Buildup and Stuck Valves
 

Just looked at your album. Really nice looking bus. One of my first jobs was at the Greyhound Depot in Billings Montana in 1965. Some of the smaller bus lines that made stops there were still using that type bus. Beautiful streamlined styling.
Looking at the combustion chambers on the head, maybe the one that was carboned up had weak ignition, or maybe it had to do with the valves out of adjustment?

Re: Carbon Buildup and Stuck Valves
 

Hi there, checked out the album. Nice looking bus. Now onto the engine.

Been sitting for a long time. There's one possible issue. Doesn't matter if the motor has low miles or not....nothing hurts an engine more than sitting for ages. Gaskets dry up....top end dries....things start to rust. And with today's fuel the ethanol does a number in the tank, lines, and carb. Draining the fuel most of the time is not enough, you'll need to pull the tanks and give them a super good flushing. Then take a look inside checking for rust. Then you'll need to blow out the lines and replace the filters. Going through the carb would be a good idea and then fully tuning up the engine. Oil change first thing! Get that black tar out and put some nice high zinc rated oil in that thing. Then remove the valve covers and check/adjust the valves to correct specs. Then clean or replace the points and coil. New cap and rotor never hurt either. Also replace the plugs....now here is the opportune time to check compression! 125 PSI is the spec from a brand spanking new engine. If finding cylinders under 100 PSI I'd say your engine is worn out and burning oil which would be a part of the carbon issue, or you have valve sealing issues.

But as it seems the carbon build up is mainly on the intake ports and valve seats I'd say that the engine was either burning old fuel, or the a/f ratio is way to rich and the engine isn't burning All of it. Or there is excessive blow by through the pcv which would cause carbon build up as well.

Weak valves springs will allow a valve to stick. And a lot of gum and residue will cause that as well. Be careful as you may have some bent push rods.

Re: Carbon Buildup and Stuck Valves
 

You don't need zinc. It was added after these engines were designed. It was added because hipo engines needed stronger springs to keep valve float from happening at high rpms . I would run seafoam for now. And check for any residue on your tanks when you get home.

Re: Carbon Buildup and Stuck Valves
 

How long did you run it on that dead hole?

Re: Carbon Buildup and Stuck Valves
 

Never hurts to have zinc in the oil. It wasn't put in oil for no reason.

Re: Carbon Buildup and Stuck Valves
 

It was put in to help hipo motors. It's levels peaked in the 80's.it's not necessary in v6. I don't advise it's use. And I rebuilt more engines last month that you will probably do in your life. I run Castro syntec 5- 50 I use about 400 gallons per year. It's bought in bulk. And delivered to my tank. And after break in it's All that is run in my or my customers rigs.