Piston Ring Problem

[slomove]

I am running a 2.0 l Zetec ZX1 (old Contour model) with individual TBs, Stage 2 cams and 10.6:1 compression. The engine generally runs very well but something bothered me for a long time: while the oil consumption is really negligible when road driving it spits out a lot into the catch can when running hot and hard on the track There is even an annoying external oil leak somewhere from the valve cover that I could never pinpoint. After each track session there is a small puddle under the car, but never when road driving.

 

Anyway, I did my first dyno session today with a few other local Seveners and pretty decent results (see below and click for full size). However going beyond 6000 rpm the engine started belching big blue clouds of oil smoke, something that I usually would not see on track, given the air flow and attention on track traffic. In the same range there is also a pretty steep drop of torque and flat power.

 

The opinion of the dyno operator and other folks present was that my engine is probably suffering from piston ring flutter. That may also explain the increased oil spillage and leakage at high revs, given the significant increase in blow-by that my (small) vent hose my just not be able to let go with consequent pressure build-up in the crank case and valve cover.

 

Any other opinions about this effect?

 

And, if this is really ring flutter, is there anything I can do about it, except for driving slow or replacing the engine? I read somewhere this may be improved by opening up the 2nd ring gap....

 

Thanks,

 

Gert

 

http://home.earthlink.net/~slomove/sitebuildercontent/sitebuilderpictures/slomovepwr.jpg

[slngsht]

I agree with the diagnosis, but not sure what options you have for curing it. You may have to go to a different design ring that is lighter, or a tighter piston to cylinder clearance... best to ask an engine builder with specific Zetec knowledge.

 

I know LS1's had ring flutter related oil consumption only during high rpm, light load (like 4K+ RPM with part throttle). Ultimately, GM went with a different piston design and modified the 2nd ring sealing surfaces to cure it.

 

[slomove]

In the meantime I took the engine apart. Nothing seems to be broken, at least. The combustion chamber has a bit of carbon deposit but that may be due to the original webers and some rich injection maps after the conversion.

 

The 2nd cylinder has low compression (195,165,195,195) and rather high leakage when tested with a leakdown tester. I took the offending piston out but nothing conspicuous that I can see, at least no broken landings or such.

 

However, I noticed two things:

 

- the top piston ring gap is 0.7mm (bottom end of bore) and almost 1 mm (top end of bore). I do not really know what is required for the Zetec ZX1 engine but I would assume it is rather something like 0.4 mm minimum. From what I read the wide gap might cause the leakage and possibly even the earlier discussed ring flutter.

 

- while the bore surface is rather smooth (only a few vertical traces), I do not see anything resembling a cross-hatch hone pattern that I read was required. Is that only worn away and normal?

 

I am wondering if I just should get new piston rings and hone the bores and put everything back together. ...

 

Any opinion?

 

Gert

http://www.usa7s.com/aspnetforum/upload/758108043_No1.JPG

http://www.usa7s.com/aspnetforum/upload/23153318_No2.JPG

http://www.usa7s.com/aspnetforum/upload/1878800884_PistonNo2.JPG

http://www.usa7s.com/aspnetforum/upload/90066712_RingGap.JPG

[gjslutz]

Gert,

 

You move fast!

 

Did you check the gap in the other cylinders with the same ring? It has been too many years for me, I also would be looking at the reason for the vertical lines. For me it would be time to have a GOOD engine rebuilder look at what you have. I sure would hate do not be 100% on and not do the best. The cost of them doing the rebuild could be well worth it. I likely would do the bearings as well while down that far. I can't add more to this, so best of luck.

 

Gary

 

 

[slomove]

Thanks Gary, that is the plan. Just need to shop for that GOOD engine rebuilder in the area but have some leads already. As for the bearings....should I just get some aftermarket shells for the Ford Contour or are there better ones around?

[gjslutz]

Gert, I would ask the "good engine" engine builder on what bearings to use. If you don't have the HP oil pump I would add one also. If they are a good Zetec builder they will know. I have one I purchased for mine when or if I pull it down for an rear main seal. You have done well getting to where you are at.

 

My feelings are not to skimp when into a job like this. You don't need to redo or loose an engine for very few extra $$$. At one time (20 years ago)I did all of my 911 Porsche & 12 cylinder engines. I never did a zetec and paid for a shop to do the P&P and stage III cams as well as the dyno tune. I think it is the best money I have spent in years. Too old to enjoy the learning errors again.

[southwind25]

only looking at the pictures...it seems as if the piston skirt is a bit more scuffed than i would want to see.

how many miles on it? i would expect at least some x-hatching yet at least at the bottom of the bore? how big is the top ridge? the top of the piston is mighty clean as well!,,and seems a bit pitted...detonation?

 

in the case of this motor (given a fair budget to work with) yeah i would do a complete rebuild with good clevite bearings. have the crank sized and at least journals polished. a good balance wouldnt hurt either. see if they make total seal moly rings for it?

 

theres really so many options!

 

my problem is..when (if) i go down the zetec road this winter, theres a bunch of little things i want to do...stuff i am just used to on my vintage race engines.. polish-balance nitride the crank.. polish-balance the rods. possible .020 over JE balanced pistons, stage 1 cams, better valves, do a little port smoothing on the head..,oh the list goes on..it's hard to stop.

[gjslutz]

Bob, my stage III cams will pull fine from 1500 RPM on in 5 th gear. It now has a good kick from 3500 up. The TQ is up from stock on so it still pulls very well on the low end. One of the big areas are in the head P&P as well as larger valve. There isn't much room to go much too big on the valves though. They were able to increase my port size enough that they also had to enlarge the intake to blend it to fit the big ports. Same with the EX. manifold. Years ago I did P&P work on my heads, but never checket with a dyno due to $$$, so I didn't know if I helped. For the $ I felt it best to have a Zetec person do it for me.

If mine comes down I'll replace the rods, or just buy the 2.3 short block all set up depending on price at the time.

[Cherik]

the "oil leak" from the valve cover is from the engine being designed for transverse mounting.

 

In the 7 it's sits for-aft and during spirited driving (esp. on track), the valve cover exit is in the wrong place and it'll throw oil from there.

I used to run an overflow bottle from the valve cover hose, and recently added a nice filter box from JEGS with a drain.

After each track session, I have to drain a couple of oz of fluid.

 

As far as the ring gap measurement, the top-bottom difference and the lack of a visible honing pattern, it looks like well worn bores.

I'd suggest to compare the cost for another block (although by now all the Contours will be "aged"), or get an

overbore and fresh pistons. A 1mm ring-gap and the .3mm difference suggest you're well past the service life.

 

Most of the bore wear is where the greatest combustion and lateral pressure exists, which is about 10..15% from TDC.

Maybe redundant is a check with a bore micrometer for bore ovality left right vs front back to confirm the wear.

 

As was mentioned, the piston skirts show some scuffing, which could be from a lot of miles or a few Wisconsin cold starts with old / thick oil.

 

 

Cherik