VVC 160 Oil Consumption & Compression - A Puzzle!

[21jigsaw]

Hi Andrew,

Interesting results but difficult to draw conclusions quite a few variables :- engine heat, clearances,oil viscosity, bore surface finish, piston clearance, engine static the dynamics of which tend to change when the engine is running.

Dave

[revilla]

Dave,

Yes I know there are a lot of variables but I tried to control them as well as I could.

I have since got the spare (believed good) engine warmed up and tested. I used identical test conditions as far as I could and the readings were again consistent across all cylinders but at about half the leakage of the installed engine, around 11-12% on each cylinder. This at leaves gives me some more confidence in the gauge I'm using

I know the units used on these gauges are fairly arbitrary depending on the spec that the gauge is built to but the instruction sheet that came with it gave some rough guideline figures which, paraphrasing, were along the lines of "New Engine 10%, 20% Maximum Acceptable on Worn Engine, 30% Major Problems". This seems to fit with "spare engine, 18K miles, believed to have no problems or significant wear 12%, installed engine burning oil at an alarming rate 24%".

In terms of the variables you mention, in both cases:

• Gauge Operation: Compressor pressure 75psi (instructions say 40psi to 100psi), gauge regulator adjusted to "set" position which resulted in a gauge input pressure of 25psi (consistent with the pressure given in the instructions). All cylinders tested exactly at TDC at the end of the compression stroke, engine rotate clockwise half a turn between cylinders in firing order 1-3-4-2.
• Engine Heat: The engine was run for around 30 minutes until the coolant and oil temperatures had stabilised. The engine was then further allowed to idle until the fan switched on to get it at the hottest point in its cycle. The tests were then completed as quickly as possible, I would say within 10 minutes for the first cylinder and within 20 minutes for the last cylinder.
• Clearances: When the new rings were fitted and after honing the liners, all ring gaps were checked as per the overhaul manual, ring clearances within their grooves were all checked and piston to bore clearances were all check, again following the procedures in the overhaul manual. All clearances were well within their service limits.
• Oil Viscosity. Magnatec 10W40 Semi Synthetic as recommended for the VVC in both cases.
• Engine Dynamics: Whilst I understand that these will affect ring seal a leak down test is always going to be done statically so there's not much I can think I could have done to improve things here.

• Bore Surface Finish: Well that's the number one suspect I think. I didn't hone the cylinders in the spare engine I tested, I had to rebuild it due to damage to the block (the original builder, whilst grinding the ribbing away to fit the Caterham starter had managed to put a large hole in it with an angle grinder than bodged it with epoxy and silver paint!) but it had done such a low mileage that, precisely to avoid this sort of issue, I inspected the bores and left them well alone, keeping the pistons, rings and liners together as intact units. That engine appears to be fine.

Given that I know it is using oil and I'm getting very different leak down results to those on known good engine, with all of the leakage going into the crank case, I think at this point I'm fairly convinced that the culprit will be the rings and liners, so I think I will go ahead with changing them and see how it goes unless anyone has got a better plan.

Fingers crossed!

Thanks,

Andrew

[Jonathan Kay]

Plan sounds right.

Does anyone offer a facility for studying the surfaces?

Jonathan

[21jigsaw]

Hi Andrew,

Did you note any difference in blow by / crankcase compression on the two engines.

Had a chance for a run down the road and a visual on overrun smoke?

As before, it seems to be across the engine not just 1 or 2 cylinders - Bore finish, ring scuffing, valve seals, cam timing?

I agree I think you have reached the point of a strip,inspection and measurement. Maybe a head swap to identify the issue

Dave

 

[revilla]

No obvious difference on blowby at idle.

 

I had Mankee Cheng follow me for 40 miles yesterday. He said there was absolutely nothing in the way of smoke, smells or anything else to suggest it was burning oil at any point, either under load or on the overrun. It went like the wind, felt absolutely happy, sounded gorgeous ... and needed a topup when I got back as usual! Most odd.

 

My wife will be away for a couple of weeks in the second half of November. I've taken two weeks off to be with the kids, but they will be at school for most of the day so I've got some decent garage time lined up to strip, examine and overhaul it. I'll write up on here what I find.

[revilla]

I've finally managed to get some time to start stripping the engine down for a look today:

• PCV pipes oily. Insides of plenum and manifold runners oily.
• Valve stems clean and dry. Backs of valve heads clean, no carbon deposits, similar appearance across all cylinders, inlet and exhaust.
• Considerable carbon buildup on piston crowns, certainly more than I would expect after 5000 miles. Carbon tides at tops of bores.
• Cylinder bores feel polished and glazed when you run your finger over them, however to look at them the honing pattern is still visibly much clearer than I have previously seen when stripping these engines. 
• No signs of scoring of scuffing on the bores.
• I've stripped the engine at TDC to give me good access to the bottom ends through the ladder. As a result I can only really see nos. 2 & 3 bores on removing the head. Will get a proper look at the others and the piston rings and skirts when I finish the stripdown (hopefully tomorrow).
• On a quick check in situ with an internal micrometer I was measuring the bores as around 80.02mm, so a little wear present but within spec. No measurable ovality (not with the kit I have anyway!).

So it does look like a failed break in at the moment, probably due to incorrect honing on my behalf, with poor ring seal and excessive blow-by throwing oil out through the PCV system into the plenum with the engine then breathing it in and burning it.

I'll finish the stripdown tomorrow and update with anything I find, then crack on with reassembly on some nice new factory-honed liners and see what happens.

[revilla]

Managed to finish stripping it tonight. Nothing really new to add to the above findings. Pistons look fine, no horrible scoring or scuffing. Other than the carbon on the crowns, they look pretty much as they did when I put them in (I cleaned them thoroughly during the rebuild). Still clean underneath, the ring grooves are free from carbon and the rings move freely. No obvious signs that they have been getting hot. Little ends look OK. The remaining two liners looked just the same as the two I was able to examine earlier. The only new thing I found was that one of the big end shells seems to have been scored by a bit of debris in the oil. Crank journal looks fine. Not relevant to the problem under investigation bit I will probably put new shells in on reassembly to be safe anyway.

 

[21jigsaw]

Hi,

Surface of the piston rings any vertical scoring / scuffing.Did you check the cam timing on stripping?

Dave

[revilla]

No blemishes at all on the rings. Shiny silver mirror edge all round each ring, no signs of scoring or scuffing. No I didn't check the can timing on stripping; maybe I should have done for more information but I was intending to check when setting it all up again.

[revilla]

Well it's all rebuilt. It starts and runs. Sounds normal. No leaks, no funny smells.

I've only run it at 2000rpm for a couple of minutes to make sure all was in order. Don't want to idle it much until it's been broken in.

That's about as far as I'm going to get for a while as they have now kindly salted the roads around here so it's gone away for the winter. It looks like I will be running it in when the spring arrives, and it will take a little while to establish the oil consumption when it has settled. I will report back.

In the meantime, the picture below shows the state of the pistons after just 5000 miles. The piston on the right is one I have removed and cleaned, the one on the left is how they all looked upon removal. This time last year when I overhauled the engine, they all looked like the one on the right. Hard coke deposits all over the piston crowns, but not much at around the combustion chambers in the head. So I'm guessing oil droplets were coming in through the inlet valves and spraying onto the hot piston crowns.

All back together again:

[Roger King]

It'll be interesting to see the long term result here. You don't necessarily have to have a visually horrible bore finish to have problems with the bore/ring interface.

Back in the 1970s we used to have the occasional 420R engine that would breathe a bit heavily on the dyno due to rings not bedding in well.

The solution?

Gently blow a small amount of Ajax powder down each ram pipe while the engine was running under light load! It often worked, but then the engine was coming apart again after only one race so who cared? Rings in those days were nowhere near so sophisticated in design or material as these days.

[21jigsaw]

Catch tank between cam cover breather and inlet manifold?

[revilla]

@Roger: Yes I had heard of the Ajax trick, however it sounded a bit too risky especially given that by the time I got that far with the problem I then understood how much ring technology had progressed! I will of course report back on the results when I get it back on the road and get some miles on it.

@Dave: I could ... but my engine is pretty much stock at the moment and I don't really understand why I should need to fit a catch tank when others don't. It feels a bit like just patching over the problem rather than identifying and understanding it and fixing the root cause. If the liner swap has fixed it I will be happy. If not, I guess that points towards your ideas of manifold vacuum and valve stem seals and then maybe be the small cam timing changes I've made may explain the issue. For now though, I couldn't really see anything on disassembly that suggested oil was coming down the valve stem seals and there was quite a bit of evidence of oil in the PCV system, plenum and manifold runners which makes me think at the moment that blow-by was the cause. Time will tell.

[21jigsaw]

Hi Andrew,

Hindsight , should have put it in place before the strip it might have highlighted where the oil was going, 

Dave

[revilla]

True!

[Wrightpayne]

Andrew,

did you get my message a few weeks ago about compressor return? I'll be at Hathern Thursday if thats any use.

Ian

 

 

[revilla]

Ian, I have sent you a PM.

[Wrightpayne]

PM back to you too!

Ian

[revilla]

An interim update; I haven't forgotten this thread.

The car has been off the road over the winter, during which time I rebuilt the engine with new rings and liners as described previously. Since then it has just sat in the garage sleeping ... until today.

The car is booked into Arch on Saturday to get a new lowered floor. It looks like it will be a wet day. I didn't want to be putting the first miles on the engine in traffic in the wet, I wanted the opportunity to work it a bit. Today looked like the only dry slot between now and Saturday so this morning I was up and out at 5:30 (it was pretty cold). Fired the engine up for the first time since the rebuilt and straight out onto the road. Fired up first flick of he key. Did a few local laps so I could limp home if I had coolant airlocks or other problems, then set off to put some miles on it once I was sure it was happy.

Cams were very chattery when first fired up but soon settled down on the move and the engine sounded beautiful. I guess it has sat for several months wth the cam lobes pressing on a couple of lifters causing them to deflate. Was also a bit of smoke to start with, probably just lube from when I assembled it, again this soon stopped. Given that it was actually icy, the oil seemed to me to come up to temperature more quickly than usual but I guess that may just have been increased friction with the rings breaking in. Once up to temperature oil and water just settled nicely at 80ºC and stayed there.

I have to say, the car seemed very, very happy. Once up to temperature I spent the whole drive accelerating and coasting but not labouring it or taking it much above 6000rpm, which was quite tiring ... I had done 132 miles by the time I got to the office! Damp roads, hovering around freezing on 15" T1Rs and wanting to give it a good push at times was certainly interesting. It would easily break traction in 1st - 3rd and you had to watch it in 4th as it kept wanting to go sideways, so no shortage of torque. Given the conditions I stuck to good straight main roads, but the sun has been out all day here and everything is nice and dry so I just can't wait to unleash it a little on my favourite backroads on the way home.

When I get home tonight I'll check over for oil and coolant leaks and check the oil level hot and running, then start collecting oil consumption data from there and update this thread on the outcome.

Really hoping it's sorted!

[revilla]

OK I did promise to update this when I had more information. Here goes ...

I've now got about 600 miles on the engine since I replaced the liners. I've been breaking it in a little less aggressively than last time, working it hard through the rev range but avoiding full throttle and full RPM.

Total oil consumption to date, as accurately as I can measure is ... zero. Right from the outset it just doesn't seem to be using oil at all any more. If anything I might have expected it to use a bit during the break in but it really doesn't seem to have consumed anything at all.

One of the first things I noticed was the colour of the inside of the exhaust tailpipe. Within a couple of hundred miles it had changed noticeably from the previous dark and slightly sooty colour to a much cleaner grey tan. You can wipe your finger round inside the tailpipe and it comes out just slightly dusty rather than black. My exhaust doesn't have a rolled lip on the end (it was grounded and mangled when I bought it so I chopped the last couple of mm off and cleaned it up square) and previously it was tending to deposit soot around the outside of the last couple of cm of the tailpipe; not any more.

Unfortunately I had some further problems after reassembling it with the Wellseal bonding of the stainless shim I used on the skimmed head, so I had to take the head off again. It at least gave me a final chance to see the combustion chambers. When I had previously stripped it to replace the liners the pistons were in a filthy state considering the fact that they had only done 5000 miles since being immaculately cleaned during the initial rebuild. There were thick black tarry carbon deposits all over the tops of the pistons from burning oil. When I took the head off the second time, the story inside the combustion chambers was much the same as for the exhaust pipe, much drier, cleaner and lighter in colour, more the sort of tan colour of healthy spark plugs.

So it's now back together with the block surface linished down a tiny bit to give perfect liner heights and a good Payen MLS head gasket used in place of the elastomer gasket and Gosnay's shim. I've done a couple of hundred miles since finally putting it back together and it hasn't missed a beat, hasn't leaked any coolant and hasn't used any oil.

It's looking rather like it's finally all sorted at the moment  

Thanks once again to everyone who contributed. Much appreciated.

[CycleSi]

Really pleased for you. I had a similar experience until I had new liners fitted and then honed properly.

[Superwhite R283]

Good to hear :0)