There was a thread on carbon fouling of valve stems not too long ago, but darned if I could find it. Searches under carbon fouling, intake valve, exhaust valves and valve stems turned up zip,zero, nada.
I'm thinking the cause might be related to a badly worn valve stem/guide, no stem seal, and inadequate PCV or massive blowby pressurizing the crankcase. All are symptoms of an old tired engine.
I'd soak the exhaust manifold nuts with PB Blaster for a week, and then might try removing the ex manifolds (with an oxy-acetylene torch handy to coax the nuts free if they are reluctant ) to gain access to the valve stems via the open exhust ports. I'd fashion an aluminum or brass chisel, and chipp the carbon from the stems with many gentle taps with a small hammer.
To prevent the carbon's return for a while before overhauling the engine I'd clean the PCV system (and maybe boost its capacity), replace the stem seals (possible on the car with the heads on) and do a few short mileage oil changes and run synthetic oil with a 40 or 50 as the second viscosity number. And maybe even throw in a can of STP or something similar.
There are no miracle elixers. In my experience, all claims to such compounds have been fraudulent.
Carbon formation on valve stems as has already been stated are the results of poor engine condition. This may be exadurated by short trip low speed use and by diluted or light weight oil.
Real answer is to repair the engine.
Bandaids as mentioned above, such as downward oscilation of the right ankle to water injection will all work to remove the symptom
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
Friends...Thank you for the quick replies.
The vehicle in question is a 1998 Range Rover 4.6HSE(P38) just turning 100K.This seems to be a common problem with this engine...I was hoping for an additive that would loose the carbon that apparently is binding some of the exhaust valve and giving me what feels like a miss. I'm the only one it bothers. I did the usual, plugs, cables, cap, rotor, fuel filter, air filters,and then finally a full round of injectors...looks like I'm R7Ring the heads next!
Min06Max I think the problem you are experiencing isn't carbon buildup but rather varnish collecting on the exhaust valve stems. I had a lot of customers with Cadillac 4100 engines in the 80's that would loose power after climbing a long hill. I believe the problem was the exhaust valve would heat up during the conditions described and expand enough to begin to bind up in the valve guide. Because the valve(s) couldn't follow the action of the camshaft the lifters would pump up preventing the valves fron seating properly. A few minutes of low speed and engine load it would return to normal operation. I am not a big fan of chemical band aids but in this case I had 100% sucess with a product marketed as mega power oil additive. I don't know if they are still in bussiness. I never saw it in the autoparts stores. Used to by it from one of the parts peddlers that called on my shop. I'd give it or some similar product from another company a shot before tearing the engine apart.---------Phil
This site has a few bizarre explanations for real life events, but nonetheless relates valve sticking to valve stem coking from inadequate oil drain back holes. Could be, I guess. I've had engine or 2 developing sticking valves or maybe lifters when anti-freeze started seeping into the oil. That same site claims the 4100 family suffered head gasket failures.
If the chemical treatment does not work, a peak in the exhaust ports should reveal if stem build up is causing the sticking. AI'd expect a peak in the oil filler hole or at worst under a valve cover would reveal the strange thin brown gray build up of anti-freeze contamination.
We were doing some testing on the dyno with a race engine,2 litre Zetec ZX3 and looking at hp changes with different fuels and in specifically unleaded vrs leaded. We see carbon build-up on exhaust valves because of the hydrocarbons that constitute some of the unleaded fuels. The next step is to look at an additive to help scavenge the tars that cause the deposits. Your problem may be because of poor valve seals but there may be other causes also.
Thank you for the reply. Information I've been receiving seems to indicate that this 4.6 engine is notorious for exhaust valve problems if an owner uses ANY thing except GOOD premium gas. Certainly once a valve begins sticking the opportunity for additional carbon build-up and general deterioration of surfaces and seals follows. I picked up some "Gunk" Valve Medic...but I concerned about it's comparability with synthetic oils...any feedback on that topic?
As explained in your previous thread that disappeared from the lubricants section, IVDs are a well-characterized problem and several fuel detergents can correct them but EVDs is a rarer and much more tricky problem because the deposits are on the post-combustion side of the chamber.
It occurs to me that modern 2-stroke engines have flapper valves in the exhaust ports to modulate back-pressure for increased low-end torque, and certain 2-T oils contain a thermally stable detergent to keep them clean & from binding. May not be the best thing for your cat converter, but certainly sounds like what you're trying to accomplish . . .
As indicated earlier, the quick and easy solution is to do a full power run with substantial amounts of water being injected.
Take care not to risk hydraulic lock by allowing water to flow or drain into the engine while it is not running.
It could be done cheaply with a windscreen washer kit, a toggle switch and a spring load push button switch, so that both switches had to be on for water to flow, thereby reducing risk of hydraulic lock.
Also water tank must be well below outlet nozzle so as to avoid possibility of syphon.
The water will clean the valves quite quickly, like in a minute or two at full load mid rpm on a dyno.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
I've received several recommendations concerning the water injection method to clean up my hanging exhaust valve(s). You’re suggestion about the dyno was the best. I will look for more details…if anyone has any incite…please write again…obviously this makes me just a little nervous…but I’m willing to give it a try.
