What Causes Intake Valve Deposits?

[Ken H.]

In disassembling my damaged engine (chronicled here - Can this Piston be Salvaged), I was surprised to see the amount of deposits on my 28K miles engine's intake valves. The head's intake runners look much the same. Any thoughts on if this is excessive, and if so, why?

 

[Firefight911]

Interesting?

 

What brand/grade fuel have you been running? Do you typically operate in the lower third, middle third, or upper third of the rev range?

 

It appears that this would definitely impact flow of the charge.

 

Incomplete combustion?

 

I presume that there have been no issues up to this point? I know, I know!! Dumb question dear Tech Mod!! Worthy of asking nonetheless.

[smiller]

I presume that there have been no issues up to this point?

It's a BMW with 28k miles on it. Of course there have been issues.

[ShovelStrokeEd]

Ken,

That does look a bit chunky considering the relatively low mileage on your bike.

 

Most of the stuff I see there looks like oil getting past the intake valve guide seals. The vapor from this can get pushed back up the port a ways during the overlap portion of the cycle.

 

I would add a set of valve stem oil seals to your parts list.

[Ken H.]

I would add a set of valve stem oil seals to your parts list.

Yeah, they are already on the list. According to the manual they have to be replaced when a valve is pulled. Something about the seal gets nicked when you pull the keeper's groove by the seal during valve removal. Not sure I buy that completely, but guess I do new seals as a matter of course seeing as I already in there.

[ShovelStrokeEd]

Near as I can tell, you have to push the seal over the keeper groove on installation anyway so why would they say something like that?

[Ken H.]

Well I'm not sure the manual makes a lot of sense on this either. I guess when you are pulling the valve down and out the lip of the seal could in theory be snagged by the keeper groove, and be folder over and in, ruining it.

 

It also says when installing new stem seals to have the valve in place, then install a "suitable sized" hose (e.g. very small) around the valve stem to protect the seal's edges as it is slid past the keeper grooves in the stem and down into place. Not sure how you would seat the seal onto the valve guide though with the stem in place? I.e. no way to use a small socket or similar as a pusher to snap it onto the valve guide. I've never any of this on on any other engine work I've ever done, so I may just put the seals in as always, then push the valve up and through. What do you think?

[ShovelStrokeEd]

I've done it just that way on probably 20 engines over the years. If in doubt, you could always obtain a small chunk of drill rod, or even a drill bit, to keep the seal centered over the top of the guide when pressing it into place. I have always just used a small, deep socket to push them over the machined portion of the guide and then, later, pushed the valve stem right through the seal. That should leave the lips of the seal in the proper orientation to keep the oil out. A little grease in the keeper groove when installing the valve should prevent any damage to the seal from the sharp edge of the groove.

[SHIMHEAD]

Hi all, just wanted to chime in on this one. There was a similar issue with valve deposits in the automotive arena back in the early 80's. It was caused by the fuel formulations at the time leaving a thin film on the intake parts that became very sticky and would trap carbon particles from the EGR sytem, and slowly build up to quite a thick layer. This layer would cause all sorts of cold start issues, as it would absorb fuel that had just been sprayed from the injectors, resulting in stalling after first start, and extreme hesitation until this layer reached a temperature where it wouldn't absorb the fuel. I was working at a Nissan dealer during this time, and they supplied us a tool to blast the back of the intake valves with crushed walnut shells, which cleaned them sparkling, and restored proper running. I also had been using Amoco premium fuel in my car at the time, and had it apart at 50,000 miles, finding my valves spotless, still using Amoco today. Still in the automotive business, and know firsthand that Chevron Techron and BG 44K fuel additives do some amazing cleaning of these types of deposits. Techron is even sold under Nissan and BMW names (the bottles are identical). Seeing as how there is no external EGR in your engine, then the carbon can come from "internal" EGR, where specific cam timing can allow exhaust gas dilution of the intake charge to help control combustion chamber temps (important for an air/oil cooled design) and NOX formation. Today's fuels are much less to blame for deposits, but I suspect this is the primary issue here. Just ask any BMW auto tech about this issue that was around in the 80's!

 

SHIMHEAD

[big-t]

Yeah, they are already on the list. According to the manual they have to be replaced when a valve is pulled. Something about the seal gets nicked when you pull the keeper's groove by the seal during valve removal. Not sure I buy that completely, but guess I do new seals as a matter of course seeing as I already in there.

 

 

 

I often find sharp edges on the groove in the valve stem that the collets fit into. Your fingers will do a better job of checking this.No big deal,a strip of crocus cloth will smooth it down.I usually do a light polish of the whole stem before assembly.(shows up any little imperfections)