Sticking valves

·         dwight eisenhart

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I have a 3300 engine S/N 1702 installed in a 230 (usa) that has had a history from the beginning of sticking exhaust valves. All exhaust valves in all cylinders have stuck at one time requiring head removal and rework. Exhaust valves on no 5 and 6 cylinders have stuck multiple times. This was mostly corrected by installing fast bleed lifters and the newer thru hole push rods with the direct lube thru the rods. Engine has 700 hrs on it. All cht are good typically running around 300 or lower in cruise.

Lately, i had a build up of oil residue on the number 6 intake valve which caused some sticking of that valve. This was addressed by replacing the lifters on that cylinder with the assumption being that there was too much oil being pumped into the head.

After about 50 hrs since this fix, i had another stuck valve on the number 6 cylinder. This time there was build up oil on the intake valve ( not as bad as before) and the exhaust valve would hardly move due to residue in the valve guide. The guides on this cylinder were replaced about 100 hrs ago so they are practically new.

So i am looking for some help with correcting this problem. The exhaust valve sticking is the most concerning to me since it was hard stuck and would hardly move ( was OK after cleaning the guide). Do not know if the intake valve oil residue is related to the exhaust valve sticking or not.

Thanks in advance

Dwight

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·         Doug Smith

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Hi Dwight,
Sticking valves can have a few causes so please bear with me - I'll limit myself to 5 questions to start with.

1. What fuel and oil are you using?

2. How are your oil temps and EGTs?

3. How much wear do you get on your rocker bushes?

4. How do you typically operate your engine? Do you do a lot of cruising or circuits? What RPM do you achieve on take-off and what do you normally cruise at? If you operate a lot at lower power settings then the higher vacuum can draw more oil down the guides, burn it and leave a residue. This can be exacerbated by the prop (I've seen a few engines with 3 bladed props have issues like this which were addressed by switching to a smaller prop).

5. Do you have the oil drain manifolds fitted to your pushrod covers?

Thanks for your patience,
Doug.

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·         dwight eisenhart

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Doug

1) using 100 LL only and phillips X/C 20 50 based on Jabiru USA recomendations. Used to use aero shell single or multi viscosity oil

2) oil temps are typically around 200 for cruise. Can go to 212 on climb but then settle back to the lower 200 at cruise. Egt for this cylinder ( no 6 is the highest of all cylinders) is typically around 1330 to 1375 at cruise. I have seen it go to 1405 or so only during decent at a certain altitude and lower power setting. Only for a few minutes though. The lowest cylinder is typicllay 100 to 150 below these values.

3) rocker bushing was replace in the past say 300 hrs ago. The wear right now has not been considered a problem. I am not sure what is considered too much wear to be honest. I think the wear was worst before the new push rods and rockers were installed.

4) i typically do mostly cruising and not much circuit work. I Cruise at 2850 almost all the time. This last trip where the valve stuck was a 3 hr cruise period. I have the new ground adjustable Jabiru prop.

5) i do not have anything extra on the valve covers. I am not familiar with any type of add on manifold for the covers.

I have sent the head back to Jabiru Usa so they can check the valve guides. There is a thought that they might be too tight and need to be opened up slightly. Let me know if you have any other questions.

Dwight

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·         Doug Smith

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Thanks for that Dwight,
I was going to ask if your valve guides had been reamed but thought that was a question too far in one session! Certainly that's worth checking and could easily be a good part of the issue.

Regarding your answers:

Ok, so no problems with the oil.

The oil temp is a little on the high side...

The EGTs are higher than I'd like... 1375 works out at nearly 750c which is getting well up there. A tuning adjustment might be in order to lower that somewhat (assuming everything else is in order - clean air filter, no air leaks in the system etc). Are you using AVGAS or MOGAS? How are the CHTs?

High Rocker bush wear can be a symptom that you're flooding the rocker chests with oil and the manifolds on the pushrod tubes can help that issue. There are some images in the overhaul manual if you're curious. I don't think I'd go that way immediately in this case but it's an option.

My first port of call after reaming the guides would be to try and lower all the temps - that should reduce oil consumption, improve head stability and help valve sealing and life - but see what they find with the guides first.

Regards,
Doug.

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·         dwight eisenhart

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Doug

The chts range from 315 on number 5 down to mid 200 s on 1 and 2. Number 6 that had the valve problem is around 300. ( all cruise numbers can go higher on climb on hot day).

The jabiru USA folks told me that egts less than 1400 were ok so i did not ask for a different carb jet. The air filter is nice and clean. The egts on number 6 used to be about 50 degrees cooler. They went up ever since the guides were replaced in the no 6 head when the earlier oil deposits were found on the intake valve. ( the lifters were also replaced to address the possiblility of too much oil being pumped in to the head). So something did change a little on this cylinder.

Reducing all the temps sounds great. How do i do that?
Mine is a stock factory built 230sp. The only 2 methods i can think of is a different jet to lower the egts, and maybe sand down the baffles in the cooling plenums around the heads. What other options are there?

Thanks
Dwight

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·         Doug Smith

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Hi Dwight,
1364 f is the limit in the manual (that's the cruise limit - the full power limit is 1292 f) and realistically you want a little margin on that so I'd certainly recommend adjusting the jets the drop those numbers a little.

Your head temps look good actually. Oil temps may drop a little if you drop egts via mixture and beyond that there's often some small gains to be had by finessing the seals around the cooler. Your oil levels also influence oil temp a bit - running around the lower dipstick mark usually works.

Taking it step by step, once the head comes back I'd try a richer mixture and see where that leads. If we're still chasing oil temps then I'll grab some photos from you and see if anything stands out.

Regards,
Doug.

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·         dwight eisenhart

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Doug

Thanks for the info. My POH has no egt reccomended numbers. I was going by what the Jab USA folks told me. Where do i find the egt recommendations for reference. I will update you on the valve guide feedback i get.

Thanks

Dwight

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·         Doug Smith

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The engine maintenance manual has the EGT limits, downloadable from this site.
Look forward to hearing back from you!
D.

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·         dwight eisenhart

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Doug

The Jabiru folks said the guide was too tight and they reamed it out to put it in the middle of the spec range. When i get it back i will watch the EGT's and adjust if needed. My EGT's used to be in the 1320 range but went up on no 6 cylinder after new guides and new lifters were installed about 1 year ago. I will double check the intake tube sealing to make sure there is not an air leak and swap the lifters since they were replaced when the EGT temps went up.

Dwight

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·         Doug Smith

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Hi Dwight,
Glad to hear they found something... And yes, a good inspection of the induction never hurts!
Let us know how you go 🙂
Doug.