Buildup On The Intake Valves ????

[beandip]

I recently pulled the manifolds on my L-24 and I found a large deposit of crud on the intake valves from the stem out to almost the seat of the valve. The stuff was thick like tar but gritty , but not abraceive when rubbed between the fingers . I removed it with a screwdriver with vary little effort. My Question is where did it come from ? I am running a air cleaner on the SUs , and the engine burns no oil and is not running rich but right on. It seems weard to me that it dident come loose and be digested by the engine . I guss I just need to drive a little harder! Anyone else have the same thing ? I have seen simular build up on exhoust valves but hard carbon but never on a intake valve. Gary

[my_mad_z]

I'm not sure if it's the same thing I had but what you have described sounds similar. When the fuel in Australia changed from leaded to 'LRP' (leaded replacement fuel) I noticed a build up of 'gunk' on the valves after changing the head. I'm not sure what kind of fuel you use, but I'm guessing it may be from the fuel. I also noticed that when I removed the spark plugs they were a totally different colour compared to normal. The colour didn't match with any of the pictures in the Haynes manual either.

I could be totally off, but that's a problem I experienced from a change in fuel additives that sounded familiar to what you described.

[nutxo]

sonetimes changing grades or even brands of oil can cause sludge,..

[beandip]

I realize that changing brands of oil can cause the engine to smoke or start burning oil , at least for a few thousand miles. But this is not the case here the brand of oil I have used hassent changed at least while I have owned the car. Going on 3yrs. as for the fuel , I always use Plus. . It just seems weard that this stuff could adhear to the valve stem sence it was soft and plyable. The valve seals do not seem to be faulty as the engine does not smoke at startup , acctually the engine dosent smoke at all. It is amazing the engine could breathe with the ammnt of crud stuck to the valve stem. The pluggs have checked to be fine however I did notice that the engine did feel as though it needed a tune up for the last few days before I pulled it. I have also found that the dist. which is from a '79zx has a broken plate that controlls the vac. advance , and that could have caused her to run a little retarted. nutxo and my_mad_z thanks for the reply. Gary

[Ben]

I would expect that it's just many thousands of miles' worth of carbon/fuel deposits on the back of the valve. One of the things that will slowly reduce the total power that you engine makes.

A good method of cleaning that kind of buildup away is to use water injection (yes, even on a NA engine). The water will dissolve the deposits in the intake tract & the back of the intake valve. And most importantly, it will steam-clean the piston crown, combustion chamber, exhaust valve/port/manifold of the hardened carbon deposits.

[Daniel]

Ben is correct the water will clean those areas.What I do is with the car hot andair cleaner off hold the car at about 2500 rpms car and pour water across a carb.You play with the throttle to keep it running.Keep it up until it bogs.Then rev until clear and switch carbs.All kinds of nasty will blow out the exhaust.I learned this years ago from the best mechanic I have ever known.As far as removing that crud.He says ABSOLUTELY NOT!! When you break it loose it will clog the oil passages.My jeep has a inline 6.It looks like black sand castles under the valve cover. It hard not to touch it but the man that I trust says Leave it alone.Oh yeah,he said the water in the carbs can be done on all cars except ford.It can knock a hole in ford pistons.Nice tip huh?

[beandip]

Well the engine is clean for its miles, when I change the oil ,which is at 3K , I can check the oil at 1000 miles and need to hold the dipstick to the light to see the oil it is so clean. The engine is in good shape , and I am not complaining it's just weard the accumilation of crud on the intake valve stems, the exhaust valves are clean of any buildup and the pistons are not covered with carbon to any extent . It's just the intakes that have me puzzled. gary

[Phred]

Hi Gary,

Long time, no see. Don't lose any sleep over that crud. Sounds like you got rid of it. I've seen many engines like that. Which doesn't make it right, not uncommon though. A very small amount of oil which slips by the guide seals over time, mixed with a slight amount of fuel is the culprit. It starts growing when you shut off the motor, the back of the valve has this odd mix on it which starts to thicken when the motor cools down. Then the process starts all over again next time you run it. After a while it starts to build up, untill it looks like what you had. The reason its on the Intake valve, is the vacume present in the intake system behind the throttle plate. The seals are good enough to keep most of the oil in check, but not all of it. You won't see it on the exh. valves because the exh. pressure blows any deposits out or up the exh. guide. If theres enough oil present in the mixture, The back of the exh. valve will get a burnt brownish crud there too.

Hang in there Gary.

Phred

[beandip]

Phred, yah it has been a long time , I had begun to think that you dident come on the site any more. I knew sooner or later some one whuld know what was causing this stuff. Question , I would have thought that running at speed would knock the stuff off and the engine would dijest it. How can I rid the valve of the build up with out having to pull the manifould ? This is on my old engine not the 54 flat top. I just want to know for knowledge. Gary By the way , a few of us Z-heads may be getting together for a burger and a beer, you interested ?