Oily residue buildup inside intake ports

[JohnDB]

Has anyone seen this gunk inside intake ports before and knows the cause?

[images below]

I was surprised when I pulled the intake manifold of my M4500 model S2600 engine (82mm stroke precombustion chamber, 6 cylinder, naturally aspirated) to find soft thick oily deposits (not hard carbon) have built up in all intake ports, from valve to about 2 to 2-1/2" upsteam of the valve into the manifold. The engine has done 5000 hours, I doubt that it has had the head or manifold off previously. The trunking from the air cleaner to the manifold was clean, no traces of dust, so I'm pretty sure its oil not dust build-up.

Possible causes that I've found through internet trawling:

1. At low engine speed/power, some boffins say that exhaust gases and unburnt fuel can get into intake port upstream of the intake valve head during intake and exhause valve overlap and and leave deposits upstream of the inlet valve. Personally I've never heard of this being a problem before. I don't think the engine has been run consistently at higher power levels in recent years (I've had it about 18 months) and find that it develops enough power for what I need at about 1200 rpm (max governed is 2800). So I can't discount that idea, but maybe you can.

2. Oil leaking past valve stem seal and down the valve guide. However, there's no sign of blue exhaust smoke, nor oil consumption. But I can think of 2 situations that might promote this problem:
(a) The tractor does get operated at some fairly extreme angles so it's possible that oil does build up from time to time on top of the cylinder head, to the valve side of the cylinder head, or at front or rear of cylinder head

(example: doing a lot of 3PH blade work on a steep slope, going across it) - but I don't know whether this is enough to cause oil to build up in the space between the head and the sides of the rocker cover, and flood the intake valve seals.
(b) Valve stem seals have deteriorated with age - the tractor is about 40 years old.

I'd love to hear from anyone who has encountered this before and identified the cause, or who can identify most likely potential causes.

If the cause is most likley failed valve stem seals, what's the best process for replacing them without having to pull the head off? And process for cleaning out the intake port passages without removing the head.

Thanks for your help.

 

[GeoHorn]

For an engine with 5,000 hrs on it... I’d be neither surprised nor concerned about soot build-up at the intakes.
When the engine is shut-down the valve stems are no longer under the influence of vacuum/pressure. This means the now non-moving valve-stems can “weep” oil into the area. Next start-up finds the area moist-and-oily which results in this sort of build-up.
The engine has operated for 5K hours this way and will do this again after a time. Don’t worry about it. IMO

 

[SDT]

Has anyone seen this gunk inside intake ports before and knows the cause?







I was surprised when I pulled the intake manifold of my M4500 model S2600 engine (82mm stroke precombustion chamber, 6 cylinder, naturally aspirated) to find soft thick oily deposits (not hard carbon) have built up in all intake ports, from valve to about 2 to 2-1/2" upsteam of the valve into the manifold. The engine has done 5000 hours, I doubt that it has had the head or manifold off previously. The trunking from the air cleaner to the manifold was clean, no traces of dust, so I'm pretty sure its oil not dust build-up.

Possible causes that I've found through internet trawling:

1. At low engine speed/power, some boffins say that exhaust gases and unburnt fuel can get into intake port upstream of the intake valve head during intake and exhause valve overlap and and leave deposits upstream of the inlet valve. Personally I've never heard of this being a problem before. I don't think the engine has been run consistently at higher power levels in recent years (I've had it about 18 months) and find that it develops enough power for what I need at about 1200 rpm (max governed is 2800). So I can't discount that idea, but maybe you can.

2. Oil leaking past valve stem seal and down the valve guide. However, there's no sign of blue exhaust smoke, nor oil consumption. But I can think of 2 situations that might promote this problem:
(a) The tractor does get operated at some fairly extreme angles so it's possible that oil does build up from time to time on top of the cylinder head, to the valve side of the cylinder head, or at front or rear of cylinder head

(example: doing a lot of 3PH blade work on a steep slope, going across it) - but I don't know whether this is enough to cause oil to build up in the space between the head and the sides of the rocker cover, and flood the intake valve seals.
(b) Valve stem seals have deteriorated with age - the tractor is about 40 years old.

I'd love to hear from anyone who has encountered this before and identified the cause, or who can identify most likely potential causes.

If the cause is most likley failed valve stem seals, what's the best process for replacing them without having to pull the head off? And process for cleaning out the intake port passages without removing the head.

Thanks for your help.

Not familiar with your engine but do know that the 1.5L turbocharged engine used in the B3350 and some high end ZT and F series mowers has exhibited issues with engine oil getting past the intake valve seals and guides contributing to regeneration issues. This has been found to be problematic on new engines with negligible hours.

SDT

 

[SidecarFlip]

Looks like a GDI engine...

 

[JohnDB]

Thanks very much guys! Very pleased to get your feedback. I will relax.

 

[JerryMT]

Since this is a diesel there is virtually no vacuum in the intake manifold. Power is not regulated by throttling the airflow as in a spark ignition (SI) engine. (That's why automobile diesels have a vacuum pump to use for the power brake booster.)
There is some slight pressure differential between the valve stem and the intake manifold, particularly at high rpm which is just the opposite on SI engines. If the valve guide clearances are large, I'd suppose some oil from the valve train lube system can enter the intake along the valve stem. Your photos appear to show the deposits to be a light color. I would have expected them to be dark and wet. The intake valves do not get as hot as the exhaust valves so the oil won't get burned off.
Flow reversion can occur during the overlap portion of the cycle when both intake and exhaust valves are open. The higher pressure exhaust gas can actually flow into the intake. Since it is hotter than the intake air, if oil is present I suppose it is possible for it to oxidize any oil that is present. That's my explanation.

If your engine has 5000 hrs on it and that's all the deposits you have, I wouldn't worry. I've never seen a diesel valve train disassembled so I don't eve know if they have stem seals on the valves.

 

[GeoHorn]

I know what you’re saying JT but of course there’s a vacuum in the intake system.... every time the intake valve opens...and the piston descends...there’s a vacuum in the intake system. And when that engine shuts down there is no longer any vacuum and oil can seep out of the valve-stem and drip down into the cyl. Then when the engine starts again, the overlap will puff some of that backwards into the intakes.
But I think you and I are hypothesizing the same action... and agreeing that it’s of little importance.

 

[JohnDB]

... Your photos appear to show the deposits to be a light color. I would have expected them to be dark and wet. ...

Hi Jerry, the photos are misleading, the deposits are mostly black or nearly black and quite damp, very easy to wipe off the intake manifold and outer areas of the ports, I've not tried wiping further in, they may be a bit firmer there. I've had to reassemble the engine to get the tractor mobile, so you guys have given me confident to leave cleaning to another day/year.

 

[JerryMT]

I know what you’re saying JT but of course there’s a vacuum in the intake system.... every time the intake valve opens...and the piston descends...there’s a vacuum in the intake system. And when that engine shuts down there is no longer any vacuum and oil can seep out of the valve-stem and drip down into the cyl. Then when the engine starts again, the overlap will puff some of that backwards into the intakes.
But I think you and I are hypothesizing the same action... and agreeing that it’s of little importance.

The vacuum starts in the cylinder when the intake valve opens on the intake stroke. But diesels run with an open intake manifold and the airflow is not throttled like a SI engine. The static pressure (pressure on the wall) in the intake manifold relatively high and I alluded to the fact that there is some differential pressure but in comparison to an SI engine which will see ~-29 in Hg in the intake manifold at idle and virtually zero in Hg at WOT, the delta P is very small and very close to zero. None the less, valve guide wear and any differential pressure can cause oil leaking into intake manifold.

 

[JohnDB]

This reminded me about a lot of stuff I'd forgotten - positive/negative pressure pulsations in the inlet manifold due to intake valve operation, cylinder pressures and overlap. It's what operates the Donaldson "vacuator" valve so it expels dust or moisture that has accumulated in the bottom of their air filter housings. Those +/- pulsations will be even stronger at the intake port, so soot from combustion or oil from valve stems could migrate up the intake manifold a ways from the intake valve.

If your engine has 5000 hrs on it and that's all the deposits you have, I wouldn't worry. I've never seen a diesel valve train disassembled so I don't eve know if they have stem seals on the valves.

Meant to reply earlier - yes this has valve stem seals.