K Series Glazed / Damaged Cylinders - Engine Gurus Please Help!

[revilla]

My VVC has had a long standing issue with high oil consumption. Very high, now around a litre every 600 miles, with no external smoke smells or other clues at all. There was a long thread here previously trying to work out where the oil was going. There have been many theories and many blind alleys.

I now know where it's going - I need to understand how it got like this.

For that reason, I'm starting a clean thread.

Bottom end was rebuilt a year and a bit ago after it was identified that my honing technique was inappropriate, using brand new liners and rings (Goetze). Oil consumption continued. It has since had two top end rebuilds with a replacement head and DVA valve stem seals, all of which were a red herring. Valve stems were clean and dry on stripdown.

Yesterday I did more leakdown tests (using a properly calibrated tester to FAA spec. at 80psi) and the results surprised me. I was hoping for a reading of around 6% leakage on a recently run-in engine, dreading getting a lot higher, actually got 0%. Cylinders were an absolute gas-tight seal. Even when I put 100psi into the cylinders at TDC there was no sound of escaping air in the crankcase which you would normally get from ring end gaps etc.

So in frustration I tore the whole engine down and took the head off again for inspection, and this is what I found:

Pretty much the same story in every single cylinder. Patches on both the major and minor thrust sides where the crosshatch was polished out to a shiny finish, almost mirror-like in places. Crosshatch was still visible on the rest of the walls of the liners, but could not really be felt with a thumbnail.

Quite a lot of vertical scuffing evident in the glazed regions too.

Also the patterns of carbon deposits on the piston crowns were very distinctive, with clean bands around the edges. Looking across the four pistons, the clean bands do appear to be more pronounced where they are in alignment with the polished patches on the cylinder walls. I'm inclined to think this is related to oil flow past the rings and not detonation or similar, but I'm not entirely sure how to read them so would appreciate any advice.

These pistons were immaculately clean 7000 miles ago, at which point brand new Goetze Service liners and Goetze piston rings were installed. Clearly the break-in failed quite badly. At the last top-end rebuild (another attempt to fix this!) these patches were visible but not as bad and I passed over them as just wear. At that point I did use a bore gauge to measure taper and ovality as best I could in situ and everything was within spec. When I built it up last time I checked piston ring end gaps, ring clearances in grooves, piston to bore clearances as per the Overhaul Manual. The one thing I wasn't able to check at the time was piston diameter and ovality as I didn't have an 80mm micrometer at the time. I'm quite sure the rings were correctly installed, the right way up, oil control rails and spring correctly assembled and gaps initially clocked as per the Overhaul Manual.

Planning to rebuild using better Westwood liners and NPR rings as recommended by Dave Andrews, but before doing so I would really like to understand exactly what has caused this to make sure it won't happen next time.

The break-in was done on Millers CRO for maybe 700 miles, working the engine fairly hard over the rev range without full throttle, full RPM or labouring, with plenty of hard acceleration and coasting. This was after an initial 20 minutes at 2000rpm to settle the cams in.

The only relevant running issue I can think of is that at a recent MOT I asked them to put the emissions tester on it and it showed a high lambda which was traced being a false lean due to a leak where the primaries enter the collector, upstream of the lambda sensor. If the lambda sensor had been reading the false lean, it may have been causing the ECU to run the engine rich and this may have been this way for some time. I wondered if bore wash during the break-in could have been a factor?

So if anyone could shed any light on those particular wear patterns and the meaning of the piston deposit patterns I would be very grateful.

Are the pistons running tight in the bores when hot? Or loose and therefore rocking excessively?

In the meantime I will try to pull the pistons and liners out of the engine tonight and I will strip one down for a thorough inspection and measure-up just to see if there anything further to be learned.

Thanks,

Andrew

[CharlesElliott]

I know nothing, but while we are waiting for Oily to show up, i would suggest ovality given the markings. Or maybe too much endfloat on the crank?

[oilyhands]

The wear patterns are at 90 degrees to the axis of the crank so endfloat wont be the issue. I do not use the Goetze service liners as I have experienced issues with them. Those marks indicate that there is excessive clearance on the liners, either due to ovality of the liner , the liner being oversized or wear on the pistons.

The oil tide on the piston crown shows that oil is being pushed up the bore probably because the oil control rings are not doing their job.

I would carefully measure the liners and pistons to see where the issue lies.

Oily

[CharlesElliott]

Am glad the oracle has arrived 

[revilla]

Thanks Dave. And thanks for confirming that the clean margins are oil tide marks, at least I know know where my oil has been going.

Managed to get all the liners out tonight. Popped one piston out and measured up quickly. Used an 80mm micrometer zeroed on a 75.00mm test piece to measure the piston, then set the micrometer to exactly 80.00mm and used that to zero a dial bore gauge. As accurately as I could measure, and only had time to do No. 1 so far:

• Piston, 8mm up skirt, perpendicular to pin: 79.95mm (minimum from Overhaul Manual 79.975mm - Undersize).
• Bore, varied between 80.04mm - 80.09mm (maximum from Overhaul Manual 80.03mm - Oversize).

Calculated clearance 0.09mm - 0.14mm (Overhaul Manual 0.01mm - 0.04mm - Way Out of Spec)

So looks like I have used excessively worn pistons in my build and have ended up with poorly manufactured brand new Goetze Service liners.

Mystery solved at last.

New set of Westwood liners on order, will get a bore gauge on them when they arrive to compare and reject if out of spec,

The problem is ... pistons. If I buy more used ones, good chance of significant wear. Even if in spec, they won't remain so for a full engine life. I don't want to go forged unless I can find some with standard CR, they all seem to target higher CR and I want to run standard management. Turbo rods would drop the CR of even the highest forged pistons too low. TF160s with rods are NLA new. Well aware of the inadvisability of reusing interference fitted rods. So it comes down to getting a set of TF160s machined for circlips or some other imaginative solution. Don't want to break the bank as I'm only looking for standard performance at the end of the day.

Ideas anyone?

Thanks,

Andrew

[Wrightpayne]

I would go to forged pistons with the little end bored and circlips as per DVAs recommendation OR another new piston route with circlips.

I think 2nd had pistons will always leave a nagging doubt!

Ian

[CharlesElliott]

All of the 1.6K race cars use forged pistons that are slightly turned down to keep the CR the same. They do re-use the interference pin and rods though which isn’t ideal. But free from engine regs you could convert to floating. 

I’m sure that Oily and others have options available. 

[7 wonders of the world]

Glad you have solved the problem with the 2 stroke K,  

Pistons wise you can buy direct from Omega, they also now own the Accralite brand too, not a million miles from you.

https://www.omegapistons.com/

I did a mini bulk buy on K pistons many moons ago and the price was very encouraging on 4 plus sets.

Would sound like a good time to upgrade to floating steel rods too, unless you compete and need to stay with stock internals ?

Max speeding offer rods to suit, yes of China origin but they make for many many top brands, I have checked several sets and all have been perfect, even the rod weight was within    0.1g - untill you added the US made ARP bolts that its !

 

[oilyhands]

On the 1600, the pistons are turned down to stop them hitting the head , rather than to lower the CR.

For those engines I may build with TF160 pistons I have the pin bores machined for circlips nd the pins shortened commensurately. They can then be fitted fully floating to either modified stock rods or steel rods.

If you want bullet proof liners, ductile iron versions with 3 times the hoop strength re available.. at a price.

Oily

[Scotland North AR]

Hi, I was using 1 litre per 1,000 miles on my 150 Sigma for 30,000 miles consistently, never got any worse. Had the 175 upgrade at Premier Power, bores found to be glazed so honed, new rings and run in on rolling road before ECU set up. Zero oil consumption in last 2,500 miles.

[revilla]

Thanks for the input everybody.

I think the route for me will be new 160-spec pistons modified for fully floating pins with circlips.

Forged pistons would be of little benefit to me as I run (and want to continue to run) the VVC mechanism and standard MEMS3 management (with a Kmaps software update). I won't be wanting push it above the current 7600rpm limit (it rarely gets up very close as it is) and I'm happy with the spec I'm at now for fast road use. In addition, all the forged pistons I have seen are for higher compression ratios; Mark at Kmaps has already advised that the map he has supplied will not be happy above standard CR.

Pistons

Genuine MGR VVC TF160 (LFL000800) pistons are available from Elise Parts (£480). However, both Rimmer Bros (£275) and Brown & Gammons (£239) stock what they describe as "OEM" pistons under the same LFL000800 part number, which was the 160-specific piston. These appear to be made by AE/Nural the (OEM supplier) and are marked as their part number 87-522700-10 which is indeed specified by Federal Mogul for the 160 engine (as well as the 143 engine).

The crown markings are different. I'd really like to get confirmation that these are functionally identical to the later pistons with the thicker ring lands and modified valve pockets - if so I'd much rather pay £2XX than £4XX for the same pistons, especially as I have a spare engine built up which I think will suffer from the same issues so I may need two sets. If however these are  more like the earlier 143 pistons then I would rather buy the Elise Parts ones.

My plan is to phone to Brown & Gammons and get confirmation from them; then order them on that basis and compare all of the measurements carefully with the 160 pistons I've removed. If they're not right, they can then go straight back and I'll have to rethink.

Whatever pistons I go for I'll need to get them grooved for circlips and the gudgeon pins shortened.

Rods

The two options here seem to be maXpeeding steel rods which can be had for around £199, or having the existing rods honed out to the correct diameter and oil ingress holes drilled for around £120. The steel rods may be a little overkill for my usage, but they are H-beam, single tang and bushed. 

Is running the fully floating gudgeon pins directly in the rod material robust in the long term? I want this engine to last for many years and a good mileage. Or would I be better to just throw in the extra £70 for the steel rods?

Liners

Westwood spun-cast on order. I want the better quality and accuracy that Westwood seem to provide but I can't see that I need ductile iron in my state of tune.

Decisions, decisions ...

Cheers,

Andrew

[Tom_Arundel]

What was the 20 minutes at 2000 rpm? Was this with the car stationary and no engine load? Engines should be run in from start with some load so don`t just run it stationary in the garage there is a good chance of glazing if you do.   

[revilla]

Both Piper and Kent Cams specify a period of fast idle 2000-2500rpm for around 20 minutes when a new cam or lifters have been installed in order to allow the cam and lifters to bed in together. The VVCBP270 came with very clear and explicit instructions on this point. I did have problems managing to hold a steady fast idle when it first started as I had deflated/aerated lifters and it wasn't running very well for a few minutes until they cleared so I took it straight out on the road but held pretty much 2000rpm for the first 20 minutes until there was heat in the oil then started working it.

[TomB]

Your notes about TF160 pistons being newly available from those suppliers is interesting - I didn't realise they were still available and relatively low cost.  if I ever choose to do a rebuild of the engine, Ill fit the stronger pistons.  

[revilla]

I'm not 100% sure yet, but unless anybody on here tells me otherwise and provided that Brown & Gammons tell me that they believe them to be identical, I'll take a punt on a set and check them out. If they're not what I hope I can then send them back. I'll post back on here what I find.

[TomB]

My biggest regret on my engine build a few years ago was not fitting a stronger bottom end when I had the chance to do easily.  At the time budget was tight so I refitted the standard ones.  

[revilla]

Well I've just spoken to Malcolm at Brown & Gammons.

It seems that:

• AE/Nüral 87-522700-00 is equivalent to the MGR MPi/VVC 143 piston.
• AE/Nüral 87-522700-10 is equivalent to the MGR VVC 160 piston (Trophy, TF160) LFL000800.

He assures me that the 87-522700-10 pistons they sell are equivalent in every way to the VVC 160 piston, other than having different lettering on the top with AE part numbers in place of the "160" pinprick engraving. Thicker piston ring lands, valve pocket depth reduced from 2.65mm to 1.00mm etc. As he put it "they're the real deal".

I'll order a set, measure up and report back!

Andrew

[oilyhands]

If they are in a  Nural box and have that number then they are the same as the TF160, I have used 30 or so sets.

Oily

[revilla]

Thanks Dave, that's just the confirmation I was hoping for. I'll drop you a PM regarding getting them circlipped and a set of modified rods. Andrew.

[revilla]

Just to wrap this up, the new pistons arrived today and everything looks good.

For future reference the pistons I bought were these: https://www.ukmgparts.com/product/mgf-mgf5-engine-engine-mountings/set-of-4-pistons-rings-160-o-e-lfl000800piston for £238.80, delivered next day for £6.48. Supplied complete with new rings installed and new gudgeon pins. They will need circlip grooves machining and the pins shortening to use as fully floating with either modified existing rods or aftermarket steel rods.

Nüral box looks right:

Piston looks to be an exact match for the original MGR TF160 piston. Ring land thicknesses and valve pocket dimensions appear to be identical:

Markings on the piston crown are different. Stamped with the Nüral logo, part number and diameter 79.990mm:

And the micrometer reads 79.990mm exactly!

[oilyhands]

Yup, thems the ones.. 

Oily

 

[revilla]

Modifications done by Genesis Engines in Hull. Pistons machined with circlip grooves. Gudgeon pins pins shortened and retained with circlips. Small ends machined out and fitted with bronze bushes, honed to size to give a floating fit on the Gudgeon pins. Oil ingress holes added. I now have four brand new pistons on my old rods in a fully floating setup. Let's just hope my oil burning woes are finally behind me. 

[SM25T]

Top marks for persistence. Fingers firmly crossed.

[revilla]

I hope this doesn't jinx it but ...

I think I might finally have fixed it! After two years of pain, several engine rebuilds top end and bottom end, multiple sets of liners, rings and valve stem oil seals ... now 846 miles since the new pistons went in and no sign if it using any oil at all.

The graph below shows the oil usage after the many attempts to fix it. The orange line tracking along the bottom axis is where I am now. I'm well past the point where the problem re-emerged when I swapped the liners and rings previously (blue line). I'll be keeping a close eye on it over the next few hundred miles, but so far so good!

I've now carefully measured up multiple sets of used 160 pistons and got pretty much exactly the same results; 79.94mm-79.95mm seems to be typically where they end up after one lifetime in a tintop vs. 79.99mm exactly when new. And brand new Goetze Service liners seem to be typically oversized too, compared to Westwoods or even compared to well used original factory Goetze liners.

Oh well ... Live and Learn!

[Golf Juliet Tango]

Andrew, I am lost in admiration at the effort you have put in, the honesty in this thread and the quality of the documentation.

You have also convinced me to leave my engines to a professional!  (that said, I need to take the K-Series out of the 21 during August so that I may clean and repaint the engine bay really thoroughly.  The prospect fill me with dread, even if I have enlisted one experienced member to help me get it out AND put it back in (the second part is more daunting than the first).