VVC 160 Oil Consumption & Compression - A Puzzle!

[7 wonders of the world]

All sounds good in the ring department then,

 

Is it just over filled and therefore blowing the excess crankcase mist out, which wold in turn be burned via as its ingested back into the engine - you could prove this be putting the breather to a catch tank and blanking the plenum connection.

Did you measure how mush went in on the first fill?

ISTR the K holds a fair bit up in the head and if you do an oil change and refill with the same quanity as the initial fill you end up overfilled.

Does it keep on using oil or does it use it then stop at a point........?

Is the dip stick the correct one / calibrated according to quantity of oil.

Wetsump Duratecs have the same issue if you overfill them - there very sensitive to oil volume !

 

[revilla]

@7 wonders of the world:

Not overfilled. It does have the correct dipstick, the Caterham-specific one with the yellow tip that is 12mm shorter than the standard Rover green tipped one to allow for the different sump design. I've been through a few hoops to get the right one for my spare engine so I'm now quite familiar with the yellow, green and brown ones and the differences.

If you do overfill it a little bit, you notice the oil temperature goes up due to crank thrashing. Usually on previous VVC engines I've noticed that even then it doesn't seem to throw much out to be burned, you usually have to let a bit out to get it back down to normal.

Unfortunately no it doesn't just use a bit and stop, it just keeps going down at the same rate per mile until it's off the bottom of the dipstick and you start to get oil surge, which is how I first noticed the problem - about 1000 miles after filling it up I started noticing the oil pressure flickering in right handers and under acceleration and it was very low. The rate of oil consumption seems to be pretty much constant whatever the level.

[21jigsaw]

Hi,

I would have thought your figures on overrun were quite high, K series limited man depression due to light oil haze on overrun - oil being sucked down the valve guides.

 

The addition of an oil catch tank will change the input parameters, increase manifold depression whereas raising the the throttle stop would decrease it but upset idle strategy

Dave.

[revilla]

Dave,

That's very interesting. When you say they limited the manifold depression, how did they achieve this? Was it a matter of constraining the cam profile, managing it via the PCV system or something else? Just wondering if there's anything else I should be checking regarding the manifold depression. I don't really want to tinker with the throttle stop screw as I'll end up with a poor return to idle and it's pretty much spot on at the moment.

If my manifold depression is higher than normal, that seems to suggest at least a good ring seal. I've gone from being convinced this was down to the quality of my honing pattern to thinking that my rings are probably sealing nicely and the problem lies elsewhere.

So here's a plan ...

First thing I will do is get myself a leakdown tester. I've never done a leakdown test before but I have watched somebody else do one (on an aircraft engine) and I do prefer to learn how to do things for myself rather than pay somebody else so this will be good. I'll beg / borrow / steal a compressor and do a leakdown test to see if that does point to particular cylinder problems.

Possible causes of the oil consumption I'm seeing seem to be ring seal (bottom end) or excessive manifold depression / poor inlet valve stem sealing (top end).

I have a spare engine, all rigged up and running on a testbed trolley. This is basically the previous engine I removed from the car when I discovered that the original builder had put a great big hole in the block whilst grinding it to fit the Caterham starter. It's had a bottom end rebuild on a replacement block but the head hasn't been touched - and I know for sure that it didn't use much oil when in use. I was planning to overhaul the head on it this winter so I have a fully overhauled spare engine. So the head will be coming off that one anyway

After doing the leakdown test, I could take the head off for a really good look at the bores, valves, seals etc. If I were to temporarily put the spare head, untouched as it is, onto the car, it would tell me conclusively whether it is a top end or bottom end problem. If it cures the problem I know I need to look at the head, so valve guide clearances, valve stem oil seals etc. The spare head doesn't have offset dowels for the timing at the moment (that was one of the overhaul jobs) so if it does fix the problem I could take some more MAP readings and put some dowels in and see if it drops the MAP on overrun and brings the problem back. If swapping in a known good head doesn't cure the problem then I will know I need to look at the rings and bores, whatever the leakdown tells me.

If that head is only going on for a short time I would re-use head bolts (subject to checking against spec of course, I've got a bundle of used but checked and usable bolts in the garage) and it would only really cost me a head gasket (and I would probably put a cheaper one on for the test rather than the Payen BW750 I prefer to use). Would probably work out cheaper than buying myself a decent borescope and I can swap a head over in a day.

When I rebuilt the head on the car I did replace all the valve stem oil seals, but I used a pack of spare seals I had in stock - I believed them to be OEM but not 100% sure so it could be that they are just not very good and the high vacuum is just pulling oil past them. If they are suspect I will swap them for known OEM ones and measure up all the valve guide clearances too while they are out - if the guides are excessively worn I'll get them changed but I'd be surprised as the head came from an engine that had only done 28,000 miles.

And while sorting out the heads I can have a really good look at cam timing the sync the rear inlets properly with the fronts.

Makes sense?

Andrew

[garybee]

Andrew,

Just seen this thread and it may be a simple one.  I noted that you mention the PCV system is drawing a slight vacuum therefore working fine.  At idle (when manifold vacuum is at it's highest) the PCV system should be closed, there is a bias spring and a weight to ensure this.  If it isn't it will draw oil from the crankcase into the inlet.

Worth a quick check before spending any time or money.

Gary

[21jigsaw]

Hi Andrew,

Yes does make sense a lot of work. 

If it were a piston / bore issue it would tend to show up on one or two cylinders. It looks towards effecting all cylinders.

I would be tempted to run down the road and get a visual of the exhaust on over run. Exhaust gases against paper might help. Reusing the head bolts is fine.(several times)

From memory the tune was modified to damp  the throttle closing / not allowing it to shut completely at higher revs. noting from your graph that depression is greater at higher revs!

Dave

[revilla]

@Dave:

A lot of work doesn't worry me too much; I get bored when I run out of engine things to play with and it's got to be better than having to throw a lot of money at it!

Will try to get a neighbour and fellow Caterham owner to follow me in daylight for a good look at the exhaust on the overrun.

@Gary:

None of my engines actually have PCV valves as such that can close! I don't have bias springs or weights ... it's all just managed through calibrated orifices and baffles. Are you sure you are thinking of K Series?

Below is my understanding of how the PCV system works on my engine. I drew the diagrams and made the notes when I was trying to get it all clear in my head earlier while thinking about this problem:

Low blow-by gas flow. Throttle closed, e.g. on the overrun. High manifold vacuum. Blow-by gases are drawn out of the cam cover through the PCV restricted orifice. Volume of gas drawn out exceeds blow-by gas flow (crankcase pressure below atmospheric) so additional fresh air is drawn in from inside the air filter via the breather.

High blow-by gas flow. Throttle open. Low manifold vacuum. Less blow-by gas is drawn out of the cam cover through the PCV restricted orifice due to the reduced manifold vacuum. More blow-by gasses are produced, exceeding the volume drawn out into the manifold (crankcase pressure above atmospheric) so additional blow-by gasses flow back through the breather to be drawn into the manifold and consumed by the engine.

That's how I understood it to work anyway; please, anyone, correct me if I'm wrong.

Andrew

[revilla]

PS: It did actually occur to me that if manifold vacuum was the issue, fitting an inline PCV valve in the hose breather might help; but it depends where the vacuum is pulling oil from. If it is via the breathers it may possibly help (although what impact it may have on mapping etc. I'm not sure) but if it is via the valve stem oil seals it will only serve to increase the manifold vacuum behind the valves and make the problem worse.

But then I thought I shouldn't be making modifications to fix a problem that other people don't have, I need to understand it properly and fix the underlying fault or cause. It's pretty much a stock engine after all.

[garybee]

Andrew,

not thinking of Ks specifically but petrol engines in general.  If the K is as you describe then as you say...nothing to fail.

Gary

[Ivaan]

How old were the seals that you used " from stock".

I understand they can harden over time.

[revilla]

I don't think they were that old, and they still looked OK. But ... maybe not!

[Mechanical Moz]

Prior to it's recent demise my 17 year old VVC would produce some noticeable oil smoke on cold starting.  I made the assumption this was caused by worn/old valve stem seals yet the oil consumption was still negligible, even on track.

[revilla]

@Mechanical Moz: I guess it would depend on which seals were failing. If I've inadvertently used some poor aftermarket seals, they would all be affected including the inlets which are subject to the manifold vacuum. If yours had just aged and hardened, the exhausts would probably be most affected as they run so much hotter.

[7 wonders of the world]

The throttle dampers were design to reduce emissions on overrun, this should not cause a problem, there are hundreds of K's runing n TB's without the damper who suffer not adverse problems with oil consumption on overrun.

There was an improvement made to the design of the oil rings ISTR, though this might only have been on the pistons used in the 1.9 versions.

[revilla]

Mine doesn't appear to have any form of damping on the throttle. As far as I can see the 52mm aluminium throttle body has nothing to stop the throttle snapping shut or to allow it to open under vacuum. But I get what you are saying about ITBs; if mine is pulling that amount oil down the valve stems then I would say something must be wrong with the guides or the seals I used. Time will tell. I will work through the plan I described, however it may take me a while to find the time to get onto it. Thanks everyone for your input as always and I will keep this thread updated when I make any progress.

[john milner]

This has probably nothing to do with the problem but there is a dampening weight on the butterfly. I think it is there to stop the butterfly flapping about under pressure. See link for how to remove it for alleged gains.

http://www.myothercarsa2cv.co.uk/howto/rovertb.htm

[revilla]

That is only present on the 48mm throttle body. The 52mm throttle body used on the EU3 VVC 160 doesn't have it.

[john milner]

I thought that my VVC had one as I remember thinking about removing it. I'll double check the next time the bonnets off. My plenum is the large plain ali type.

[revilla]

Is yours an EU2 or EU3 VVC? I was a bit sloppy with my wording in my previous post. The EU2 143bhp VVC still used the 48mm TB which will have it. The EU3 160bhp VVC used the 52mm TB which won't have it. For future reference I will edit the previous post to refer to "EU3 VVC 160" rather than "VVC".

[p.mole1]

I had the same problem years ago with an A series engine overbored to 73.5mm.The bores had glazed and the I assume the oil control rings never worked properly.

The car used loads of oil but never produced a hint of blue smoke whatsoever.

[john milner]

EU3 early 2003. I have always assumed that it is a 160.

[Roger King]

From the description, you have to be burning the oil since it's not coming out anywhere.

Bore finish is one of the most boring (pun intended, but unavoidable), but most important parts of an engine build. Back in the day, it was quite common to come up behind a slow car with "running in, please pass" on a sign in the rear window whereas these days you are generally advised only to avoid thrashing a new engine.

If you examine a honed bore surface under a microscope you will find that it is a series of peaks and troughs. During running in, the piston rings have to remove those peaks and leave you with a flat surface that has troughs in it; these retain tiny amounts of oil that lubricate the piston rings as they slide up and down. It is very easy to get this wrong and end up with a torn and damaged surface that allow excess oil past the rings. BUT THAT WAS IN THE OLD DAYS.

Modern engines nearly all use what is known as a plateau honed bore finish. This really just involves finishing the bores with a plateau hone  - a device which removes all the peaks from the bore finish without having to run the engine. Effectively, this leaves you with an engine in which 90% of the running in has been dealt with before it is even fired up for first time. This bore finish gives lower friction, less oil consumption and better sealing. Although not ideal, oval or tapered bores have a very small effect on performance when compared to a poor bore finish.

When I started building competition engines in the 1970s, we used to hone the bores dry, with no plateau finishing. Typically, around one in five engines would have oil consumption problems. Later we changed to wet honing and finishing with a plateau hone and I have literally never had a single problem in this area since.

[john milner]

Just to put the record straight my ECU is 160, TB is 52mm and I was wrong there is no wedge. Seems odd though that the 48mm has a wedge but not the 52mm.

[oilyhands]

The wedge is there to soften the throttle response on the initial 20 degrees of throttle movement. This reduces the tendency for the engjne to kangaroo. The 52mm TB was fitted primarily to performance versions of the engines where quicker throttle response was valued over this.

Oily

[revilla]

I managed a leak down test tonight. The results don't look very encouraging. The leak down test was done with the engine fully up to temperature. The tester I used was this and it appeared to work consistently (after I removed the Schrader valve from the cylinder adapter pipe, which was clearly intended for a compression tester not a leakdown tester and showed zero leakage even when not screwed into the cylinder as the valve closed under pressure - I guess you get what you pay for!). I followed the instructions exactly, regulated pressure from the compressor was 70psi and the test pressure required to zero the leakage gauge was about 25psi.

Cylinder	Number 1	Number 2	Number 3	Number 4
Leakage	23%	23%	24%	24%
Picture	[attachment=11115:name]	[attachment=11116:name]	[attachment=11117:name]	[attachment=11118:name]

Just for comparison and to sense check the gauge I also tried it on a spare engine that I know wasn't burning oil when in the car. I couldn't run that engine up tonight so it was stone cold but it still read less than 15%, it would probably have been quite a lot lower hot.

Each cylinder was tested at TDC at the end of the compression stroke. With the compressor attached to each cylinder I listened for escaping air in the plenum, in the exhaust and through the oil filler cap. In every single case the air was going past the rings only. Absolutely no sign of valve leaks, just clear hissing in the crankcase.

So what do people make of those results?

I was hoping for somewhere around 10%. I would interpret leakage that high on an almost new engine as meaning that break-in had failed and the rings weren't properly seating, and I'm guessing my oil is being thrown out to the plenum with it breathing heavily in blow-by under load. The fact that the readings were so consistent across all the cylinders suggests to me that it is less likely to be specific damage, probably just poor or unsuitable surface finish (by me  ).

@Roger King: Thanks for your insights. Sorry I didn't respond earlier, I've been away from car things with work for a few days, but I do appreciate all input. My liners weren't plateau honed, just done with a three stone hone. As you say was done in the good old days. I guess we live and learn.

It will be best part of a month before I get time to tear the engine down to fix it. What do people think I should do ... carry on with the diagnostics I suggested earlier, swapping the head? Or are these results pretty conclusive and I should just get on and replace the liners and rings?

Thanks for your thoughts,

Andrew