VroomVroomVroom

I have a wear problem on my '86 GXL engine I hope someone can explain. An apex seal failed at 220,000kM, prompting me to try my hand at repairing the engine. I like to know why it failed (beside the high milage), and have examined the remains for clues. Most disapointing is to discover that both stator housings are scrap, due to a 1/10" wide gouge all around the rear edges.
The engine displayed several signs of distress, poor idle and hard starting, before breaking on the previous owner. I bought the car as a basket case.

I have made some measurements that might shed some light.
The housing is 3.169"
The Rotor is 3.155"
The top apex seal is 3.058"!

Thus the rotor to housing clearance is 14 thou.
And the apex seal to housing is 111 Thou!

The triangle part of the corner seal has a 1/10" flat worn on it that matches the gouge in the housing. It seems to me that this can only occur if the flat end of the apex seal wears excessively...which indeed it has, and allows the triangle to move upwards.
Anyone have any idea what could have caused this?
What precautions do I need to take on the rebuild (another engine) to prevent this? Thanks, Dave

Black13B

iTrader: (1)

lack of lubrication?

carbon buildup?

Icemark

stuck seal... Probably either carbon build up, crappy gas, or crappy oil.

Black13B

iTrader: (1)

really? can you elaborate on this one? never heard of that before..

Icemark

Well crappy gas will lead to increased carbon build up.

Gas is kind of like oil... it all comes from the same place, but the company specifies what additives go into it at the refinery.

But then sitting in the tanks at the gas station, it is not un-common for (shall we say unscrupulous) owners to dump in extenders into the gas such as methanol or ethanol and usually anti-knock ingredients as well (since methanol tends to light faster). All these extras extend the gas, that the station gets an extra 3-5% or so sales off of that last load of gas from the tanker. Hey if you could increase your profit by 3% on every sale would you?

Well gas that burns too early or has too many additives in it is much like oil that has too many additives in it. When it does burn, it either burns incomplete (leaving carbon) or it burns leaving a high ash level (what is left after it burns) again leaving deposits on the combustion chambers and seals.

Black13B

iTrader: (1)

ahh i see.. never knew that before..

Icemark

Haven't you ever bought a tank of gas and the car just felt like it wasn't running well, until you get a new tank of gas from somewhere else???

Black13B

iTrader: (1)

actually yes.. all i thought was "crappy gas".. i knew it was out there, but i was unsure of the "scientific properties" of it, if you understand what i mean

VroomVroomVroom

Well ice, I'm pretty sure bad gas is not the reason for 0.110" of wear on the ENDs of the seals. There was a normal amount of carbon deposits on the rotors.
If I get a tank of poor gas, I don't go back to that station. So you could say only one tank in 100 would be "bad".
As for crappy oil; are you saying the lubrication was inadequate? If so, I would have expected the bearings and E-shaft to show signs of wear, which here is not the case. The rear plate has quite heavy wear on it also, though I have not got an actual measurement on that.
I guess I was looking for a mechanical reason, like incorrect assembly, or clearances were wrong.
The Torrington bearings and thrust plates look like new, so I would say that the end play, and oil quality were not an issue. Needle bearings rotate at extreme rpms, and are the first to suffer from lube problems.
Anyone got anything to add? Thanks, Dave

Icemark

I was thinking that the build up was forcing the seal to stick. How do the apex seals look??? were any of them stuck low (compressed) as well??? I thought so from your description... if so, then I go back to the dirty intake of either air or fuel or poor quality oil.

HAILERS

What's the combined thickness of the two apex seals? I'm refering to the fsm where it says it should be 0.315 as the standard height and then the height limit as being 0.256.

Is there much left of that side piece (triangular piece)?

Why wore out?? Maybe toooooooo much cranking of the engine when flooded. That washes lubricant away from the seals and causes imho premature wear. That's why if I give one of my half *** answers about how to unflood the car, I try to eliminate all the excessive cranking of the car and try to find out if the car is getting spark without having someone crank til the starter is junk and the oil is washed away from the seals. Anyway, just one reason they may be a bit worn.

Is there any evidence of someone being there before you when you disassymbled the engine? You know, excessive rtv around pan gaskets etc? Maybe someone rebuilt it and just replaced the water seals and left the old apex seals in place (probably mixed them up upon reinstall).

VroomVroomVroom

ICE, thanks for the suggestions. No---the apex seals were quite free, in fact one in the rear was missing LOL, the reason for the tear-down. The engine is scrap, so I am using it for the experience, and to try to understand the failure modes. Everyone talks about the apex seal failure...but not the actual cause!
I used to tune 2-stroke engines, and piston ring failures were usually caused by too wide a transfer port for one. I liken that to what we have when the apex passes the exhaust port at high RPM. (could that be why the new Renesis ports are on the sides?).
HAILERS
...Whoo...apex seal height is 0.229"! (estimated as its very difficult to measure with that sloping angle between them).
That is way below min. height (for re-use anyway).

This engine suffered from very hard starting for some time before failure, probably due to horribly low compression from the wear I see, and not as the PO supposed from flooding. In any case, from what you are saying, the engine being cranked excessively would have washed the oil away, and resulted in the wear I measure. Thanks for the diagnosis. Dave

VroomVroomVroom

No-one appears to have had the engine apart before. The side seal triangle pieces all have a 1/10" flat on the bit that contacts the housing. I shall attempt to post a pic. Dave

HAILERS

It probably really did flood on him. That's because of the low compression. We hate to see posts asking *why is my engine flooding*. There is a very good chance that its the low compression. i.e. worn out engine. All the wear wasn't from cranking a non-starting engine, but I bet it takes a lot of life off an engine.

Yuppers. The low apex seal height explains the short length of the apex seal. I'm pure novice. There may be other and better answers. But that's my answer.

EDIT: You might take a look a the oil injectors and see it they are working. You should be able to blow only in one direction on the injectors. Thats towards the engine. All four.