Inlet valve deposits

[mike3md]

I have just taken the inlet manifolds off a couple of engines with about 6000 miles since full rebuild, and was surprised to see carbon deposits on the back of the inlet valves. Both are fast road with gas flowed heads and driven quite hard, with one of them having done Spa twice, and run almost exclusively on VPower.

 

I can clean up the valves with a piece of rag and and dowel, but can I expect this to get worse, and what can be done to avoid it? Both engines have been set up on a rolling road, and never used for short journeys.

 

Thanks

 

Mike

[Ashley James]

Assuming the guides are not worn, you may be able to fit valve stem seals that will restrict the flow of oil down the guides. Most modern engines use them and they are available in an enormous range of sizes.

 

If there's not room for them because the lift is enough to damage them or they don't clear the springs, you can have recesses turned inside the guides and use O Rings as Ducati and Rover used to.

 

Any good engine shop should be able to help. FWIW Dennis Welch does a conversion for AH 3000s and Ive fitted some to my MKVI Bentley.

 

Ash

[Tom Fremont]

I use an additive in my fuel and select Shell whenever possible. At 10,000 miles on the most recent head ( now at 70,000 ) I discovered copious amounts of tar around the stem and back of the inlet valves on my driver. I managed to clean them off with solvent through the head, still installed and have used STP gas treatment thereafter, switching recently to SeaFoam. Looking through the spark plug holes it seems to be doing the job.

 

I didn't think it had to do with oil getting past the valves, but rather partially burnt fuel getting baked on when the exhaust gases are passing back and forth, a condition aggravated by long duration cams. ( Oil consumption is ~ 3000 miles/ quart. ) Fuel brands are claimed to be a big factor for better or worse, ironically that with a UK name getting the worst rap at the time of my discovery.