Lycoming Cylinder - Troubleshooting

Guys,
I need help a little here, at least some inputs or ideas on my #1 Cylinder

- First one to lean, always before others
- little morning sickness when sitting for a couple weeks,
- GAMI Test, I notice that this cylinder spread is 1G more than others
- Spark plugs have more carbon deposit ( nothing alarming) others are clean, (I Have seen a little oil in cylinder when sitting for a while)

All others cylinders look the same, GAMI spread of 0.3 between others, plugs all greyish / white

I have heard Lifter, cam, perhaps valve sticking, etc. Would like to get your inputs on this one

Lyc. o-360 A1A, 500h SFOH, otherwise stock

As you have a carb instead of FI, look for why this cylinder is running so lean. One data point you can do is GAMI spread on this cylinder at low power vs WOT. If the GAMI spread is not as bad at WOT, then I?d look for and intake leak that is leaning this cylinder.

The stuck valve may be a symptom of the problem, not the problem itself. Either way, ream the valveguide as it needs ot be done anyway.

I?ll let those more experienced comment on the valve discoloration.

Carl

Adding to Carl's info, I would suggest a wobble check of that intake valve. While watching with the bore scope, see if the valve shifts as it closes.

The burning and seat appear abnormal to me compared to valves I've seen - though I am no expert either.

morning sickness is typically a sign of sticking valves. On your picture of the exh valve (pic #2), you can see black carbon build up (coked oil) at the base of the valve guide/bore and what appears to be vertical markings on the valve stem where it may be rubbing on the build up in the guide.

This is a common problem on lycomings and they provide a procedure for checking it - wobble test). The fix is straight forward and a member here documented the process with pictures.

Larry

Thanks guys, all great ideas which makes a lot of senses. I will take the cylinder off and end it to the shop, better off keeping them In Good shape!

I read 400h and sticky valve, why, what causes this? I have read many many pages today on sticky valve and yet not fully undurstanding causes.

Thanks
Dayz

I may take some flack for saying this, but Lycoming 'allows' a fairly hot maximum Cylinder Head Temperature. I won't fly my heads that hot, 320F is about perfect for me, but 400 seems extreme, and the valve stem is much hotter than that. Oil starts 'coking' at about the middle 300s?, so if you think about it, you know its best to keep those CHTs within reasonable limits.
A 'pull' from a Lycoming O-360 operating manual: "For maximum service life, cylinder head temperatures should be maintained below 435?F (224?C) during
high performance cruise operation and below 400?F (205?C) for economy cruise powers."
Section 3 of this manual allows 500F as the max head temperature, I would never want to go there.
My RV-8 has a reconfigured IVO-360 from a Brantley Helicopter. It has oil pipes that run from the oil galleries in the block to the heads where oil cools the outside of the exhaust valve guide. Helicopter engines must lead a tough life.
The same operating manual recommends an ideal oil temp of 180F & max oil temp of 245F. If your heads have been run hot and the oil temp with them, I believe you can expect to have heat damaged exhaust valves/guides.
If only on one cylinder, I would look for a lean mixture problem, like a leaking intake hose or gasket at the head, and a cooling problem like grass or remains of a birds nest in the cooling fins.

Scott, I think I?m in agreement with you on this. I keep my cht?s under 400 and cruise in the mid 300?s, but I had worn exh guides in 300 hrs from new cylinders....on my 2 hottest cylinders.
Kevin Eldredge makes CNC valve covers with oil ports aimed at the exhaust guide. I hate the idea of external oil lines, but if I see early guide wear again I?m going to give them a try. I suggested Ross add them as an option on his covers here:http://http://www.vansairforce.com/community/showthread.php?t=155999&highlight=CNC

Tim Andres

Dayz said:

Thanks guys, all great ideas which makes a lot of senses. I will take the cylinder off and end it to the shop, better off keeping them In Good shape!

I read 400h and sticky valve, why, what causes this? I have read many many pages today on sticky valve and yet not fully undurstanding causes.

Thanks
Dayz

Click to expand...

Lycomings suffer from an anemic oil flow to the rocker box, due to a compromised lifter design. In a well designed engine, the oil flowing to the rocker box helps to cool the upper part of the head and more importantly the valves. This lack of cooling causes the exh valve to run hotter than is should and this heat bleeds to the valve guide. When the temps of the oil in the valve guides gets to its critical level, it cokes (i.e. burns and becomes an oxidized solid). This solid, coked oil gets deposited on the valve guide and this reduces the clearance between your valve stem and valve guide. The guide's bore diameter shrinks a bit when cold and grows a bit when hot. This is why typically/initially the valve sticks only until the engine warms up.

You can run a reamer through the guide "in situ" to avoid the hassle of pulling a cylinder, once you confirm the problem. It's an easy job, your just removing the carbon crust from the valve guide.

Larry

Dayz said:

Thanks guys, all great ideas which makes a lot of senses. I will take the cylinder off and end it to the shop, better off keeping them In Good shape!

I read 400h and sticky valve, why, what causes this? I have read many many pages today on sticky valve and yet not fully undurstanding causes.

Thanks
Dayz

Click to expand...

You might consider either doing or having the engine shop do a wobble test before removing cylinder. If the valve guide needs reaming the shop would be very close to doing that without much more labor. For this repair, Cylinder removal shouldn't be necessary. And a lot less expensive

Upgrading to the IVO-360A1A cylinder with oil cooled head is probably not an option. I just checked A.E.R.O. direct parts, and although the IVO-360A1A is not specifically mentioned, the IVO-540 variants (Six cylinder instead of four, but probably the same-ish) run $3100-$4300 each! Additionally, the Lycoming branded ones are out of stock. I just looked up cylinders that might fit my narrow deck engine, so I have no idea where you might need to look.
A person could copy the oil port (and exhaust valve guide) into the heads and drill/tap the block, and fabricate the lines, but I don't know who does it. Big Job.
The idea of fingers inside the rocker cover to redirect oil flow is a good one; my 1969 Pontiac Firebird has those (stock!)
That seems a more attainable (but less effective) mod.