JE878 gone bad

[misterdimwiddy]

woah lets not all jump to conclusions here talking about design flaws of the upgrades that many owners have done with no problems.

I think the key point to focus on here is the fact Phils engine was suffering with low oil pressure from the outset.

Could it be not something as obvious as oil starvation caused by a poor oil pump?

Just seems odd that there are a lot of 878 kitted bikes about that havent had any bother.

That said I doubt I will be doing anything with the internals of my 900 engine. its quick enough on the track for the rider to be the difference.

I am fairly certain revving the bikes hard is not going to kill the engine. mine will be getting a good kicking for the foreseeable future.

I agree with the above and my intention when sharing this info was not to freak everyone out that has an 878 kit + other mods. I am not suggesting that the JE piston design is flawed.

Thinking through the varied and interesting comment here I am still trying to conclude the ultimate cause of my small end/piston pin wear which has occurred at quite low mileage.

So far this is where I am (its a bit long winded but my head is spinning with problems and solutions);

My original high mileage tired motor had the 878 in for about 4 track days before fitting FCR's (88rwhp). It was burning some oil and the oil light was on a fair bit at low revs when hot. I ignored this because the switching pressure of the VW pressure switch is less than 1 bar from memory and I did not believe that true pressure could be this low. Typical oil pressures are up at 60psi ish I believe.

The crank then died (LH big end) confirming that I really did have low pressure. Mains and big ends were all very worn (out of spec clearances) and the bores showed wear on the thrust faces at that point. Small end wear meant new rods and pins but when it went together with a new crank, I did not recognise the possible significance of the bore/ring wear (should have addressed this at that time).

Motor then did 5 more track days before the head came off revealing the current wear to what were new small ends/piston pins.

The circlip ends of the piston pins are not damaged significantly indicating that lubrication here is effective.

My bore/ring wear (top ring gap is 0.7mm from what was 0.3 when first installed) I believe originates from running the motor hard with the knackered crank. Large bigend/main bearing clearances, low pressure and subsequent inadequate oil spray under the pistons from the jet in the top (rear side) of the rods has led to high wear here. The small end of the rod I believe is lubricated (through the two holes in the small end) from this same oil jet rather than simpy relying on oil splashed from the crank/rods. Splashed oil would be minimal I think in a dry sump motor. I also question whether the small end would be lubricated with oil scraped from the bore by the oil rings. The piston pin ends have oil fed from the scraper rings in the JE pistons (not through the 2 wholes in the stock piston) and I suppose you could argue that some of this will end up on the conrod small end?? I think that obstructing the feed jet in the rods would be terminal.

New crank + oil pump in spec should have sorted my low oil pressure giving effective oil spray under the piston crown from the rods. This did not help my already worn bores but should have given sufficient small end lube I believe.

So, why have I got rod wear when pressure is good? This is my main concern as I rebuild the motor from this point.

At the moment I think that the (considerable) bore wear may have left the piston inadequately supported enabling it to rock laterally which has induced wear at the small end despite there being lots of oil around. The visible loss of contact between the rings and the liner would also mean that less oil would be scraped from the bore and so feed to the piston pin would be reduced (even though I still think this is primarily fed from the rod oil jet).

I will compare the level of piston movement possibe with my worn JE's against that of a stock piston in a stock bore to back up my theory.

My plan is to change the rods (luckily I have a good pair in my box of bits) which I will have shot peened this time, rebore some other barrels that I have to give 0.08mm clearance with my worn pistons + new rings (correctly gapped) and pins to effectively give me a new (ish) motor from the barrels upwards.

I will fit an oil temp/pressure gauge if possible so that I can monitor what's going on in the world of lubrication.

The motor's out already and I am hopeful that I can get both rods off the crank without splitting the cases again. Much easier sorting this lot without being on my hands and knees out in the cold (especially cam timing).

Thanks for your collective thoughts; it will keep me awake at night until I have got it sorted.

[cobbadiggabuddyblooo]

I'm sure it will all come together well for you this time and yes I stand corrected the 4 holes in the std piston are the bleed outlets for the oil fed to the pin from those holes in the rod as Rod pointed out. It pays not to work from a mobile ph and peruse what you right before sending.. Once you have the rods out and inspect the wear on the big end bearings, This will be a good indicator for loss of pressure. If there is wear at this point and all you points along the oil feed are fine ( check the gauze mesh filter inside the sump, mine was being restricted there too) then just keep following the chain. Slow n steady wins the race .. Good luck and stay positive

[misterdimwiddy]

I'm sure it will all come together well for you this time and yes I stand corrected the 4 holes in the std piston are the bleed outlets for the oil fed to the pin from those holes in the rod as Rod pointed out. It pays not to work from a mobile ph and peruse what you right before sending.. Once you have the rods out and inspect the wear on the big end bearings, This will be a good indicator for loss of pressure. If there is wear at this point and all you points along the oil feed are fine ( check the gauze mesh filter inside the sump, mine was being restricted there too) then just keep following the chain. Slow n steady wins the race .. Good luck and stay positive

Thanks Cobba

I am not distressed by the condition of my motor. It gives me something to do between now and spring and it's almost nice having the motor up on the bench again. I know the thing so well now I hardly ever need to refer to the manual.

Another mod I am considering is a baffle in the oil tank. The pump pick up point is at the lower rear end and I think that under repeated hard braking (track use) it could easily get big mouth fulls of air as the oil surges forward especially if the level did get a bit low.

Rods are coming out today and I will be on a downer if the big ends they are damaged

[misterdimwiddy]

It's a bit tricky but you can remove both rods with the cases together.

Big end journals and bearing condition is perfect; phew

Swapped rods using existing shells and checked clearance with Plastigage; both at 0.06mm (same as when the crank regrind was done) so OK; Yamaha spec is 0.02 to 0.05 with 0.09mm max. Have read that greater radial big end clearance will increase the oil flow to the underside of the piston so I am happy to be at 0.06mm.

A good result.

Rods off for peening this week and I can put it back together with a rebore, Kent cams, head skim/porting etc

My current diagnosis in summary is as follows;

Knackered high mileage motor + JE and FCR's gives low oil pressure and crank failure + rapid piston/bore wear. 10/40 oil and over revving has aggravated things I believe. Heavier JE pistons making things out of balance is another factor maybe + 20hp over stock. I will determine the weight difference and machine he JE's to suit.

New crank running with the same piston/bore wear has led to further piston skirt wear (and less effective heat transfer to the liners) and ring wear/blowby and eventually lateral piston rock which has then resulted in small end wear. The small ends are only worn on the outer edges, not in the centre of the bearing width. If small end lubrication was bad across the whole bearing (from oil starvation) I would expect wear everywhere within the small end width.

JE pistons are not slipper type as the cast Yamaha ones are and so I would have thought piston rock would be less of a concern (unless wear is high); I need to check the actual piston to bore clearance as they are now against the 0.08 spec.

I am reasonably confident that this time it will stay together and not burn a drop of oil

[Rod.s]

It's a bit tricky but you can remove both rods with the cases together.

Big end journals and bearing condition is perfect; phew

Swapped rods using existing shells and checked clearance with Plastigage; both at 0.06mm (same as when the crank regrind was done) so OK; Yamaha spec is 0.02 to 0.05 with 0.09mm max. Have read that greater radial big end clearance will increase the oil flow to the underside of the piston so I am happy to be at 0.06mm.

A good result.

Rods off for peening this week and I can put it back together with a rebore, Kent cams, head skim/porting etc

My current diagnosis in summary is as follows;

Knackered high mileage motor + JE and FCR's gives low oil pressure and crank failure + rapid piston/bore wear. 10/40 oil and over revving has aggravated things I believe. Heavier JE pistons making things out of balance is another factor maybe + 20hp over stock. I will determine the weight difference and machine he JE's to suit.

New crank running with the same piston/bore wear has led to further piston skirt wear (and less effective heat transfer to the liners) and ring wear/blowby and eventually lateral piston rock which has then resulted in small end wear. The small ends are only worn on the outer edges, not in the centre of the bearing width. If small end lubrication was bad across the whole bearing (from oil starvation) I would expect wear everywhere within the small end width.

JE pistons are not slipper type as the cast Yamaha ones are and so I would have thought piston rock would be less of a concern (unless wear is high); I need to check the actual piston to bore clearance as they are now against the 0.08 spec.

I am reasonably confident that this time it will stay together and not burn a drop of oil

Now with all the information, it all makes sense.................still don't like the design of the JE's

Have fun with rebuild and keep us posted

[misterdimwiddy]

Weight difference of piston + pin and rings is as below;

Stock 409g
JE 448g

As Cobba said, most of this difference is from the thicker JE pin; not sure why this is so different from the Yamaha one. Higher forces no doubt in that region from the power increase but enough to distort a stock pin? Could reduce small end temperature perhaps (and help prevent wear and poor lubrication damage) because you have heat going into a larger piece of metal?

I am going to leave the pistons as they are and hope that the imbalance is not an issue. If you weigh and look at a 40g piece of ally this is a lot of material to lose from a piston and I cannot see where you would remove it from safely. I think that chopping lumps off a forged item is not a good idea unless you have experience doing this.

Mobil 1 20/50 fully synthetic will be my oil choice to keep high temp viscosity up plus an oil temp & pressure gauge, oil cooler if temp is above 80/90°C.............??

[dandywarhol]

Q's......
Should we plug the oil holes in the rod?
Should we plug the top holes in the rod as they are redundant?
Should we direct the bigend hole to the upper side (top) of the bore?
When you assemble the rod and piston was the hole facing up or down?
Have the bigend bearing shells be correctly fitted to allow the oil out to cooling etc?
Can we just reverse the bearing shells to block the lower hole giving us better bigend lubrication?
Should we attach an oil flicker to the lower con-rod bolt to spray/flick oil onto the bore walls?

Dose any of this really matter?



Rod

I certainly wouldn't block any holes in the rod. The hole in the photo is to spray the underside of the piston to lube the small end and cool the piston crown - it is designed at that angle for the crown cooling.

I don't want to put another spanner into Phil's works but I'd be having a close look at the big end bearing surfaces with that amount of swarf coming off the pins.

[cobbadiggabuddyblooo]

[quote="misterdimwiddy"]Just waiting for my skimmed head to be finished and the motor can go back together with Kent cams and 11.85:1 CR. The joy of cam timing awaits me.

While it is in bits I thought I would remove the barrels to check the bores (it has been smoky for a while). Did not want to fork out for valve seals and head gasket only to find that it is still burning lots of oil.

I have opened an almighty can of worms by doing so and it's all bad.

Both gudgeon pins are damaged and rock laterally in the small end. Rods do not look bad but I have yet to measure them.



[url=http://s1104.photobucket.com/user/miste ... 1.jpg.html][/URL

LHS of pin is the circlip (piston) end, the gold coloured section is the original machined surface and then the RHS is the small end surface

Magnified 50 times it looks a whole lot worse!!

Looking at your pin, the ends are fine as you can see, these are fed through the piston from the oil scraper rings.

The centre of the pin is fed through the holes in the top of the rod and obviously these are fed from oil sprayed up to the underside of the piston crown.. Is there any blockages in these point? Once you stretch that bottom cap, you will begin lose oil pressure.
So the piston design for oil feed to the pin on contact with the piston is not an issue.
Oil feed to the pin on the rod looks like the culprit..



Here's the pin off my std piston at 125,00km
But the rod had a previous loss of oil around 80,000km previous.
Photos are here on this link..
viewtopic.php?f=5&t=9570

Compare all the photos, The oil fed to the std pin and piston is sprayed and is ejected where the pin passes through the piston so oil feed to the pin was still not too much of an issue.
The pin on your motor is recieveing oil just fine on the piston, just feeding the small end is the issue.
This is fed from pressure from the crank.
Even with my worn bottom end shells I still managed to find enough oil to keep the smallend to some degree of flogged out normallity if I can put it that way...

Does this all make some sort of sense where the maybe where the issue lies to start?
Or is this damage from piston/ring gap and wear on the bore creating movement?

[misterdimwiddy]

I've now checked the big end condition which is excellent. Clearances are within spec and no shell bearing damage.

Measured JE skirt clearances are 0.08 and 0.09mm so v close to spec. Side to side clearance is much larger (0.35mm!!) but there is no wear on the piston sides so this is as it should be. When you pop a JE in the bore it really does have quite a range of movement. Piston OD at the top is 90mm (in a 91mm bore).

Rings when pushed square into the top of the bore show no radial gap against the liner (which is very apparent towards the bottom of the liner). I therefore have definite liner wear (ovality). Ring gaps are 0.7mm so they are definitely worn (start at 0.3 to 0.4mm).

My current opinion is that I have bore wear originating from running with low oil pressure before my crank went in April this year.

I am now less sure that piston rock arising from bore wear has caused the small end/pin wear. This I feel is more likely to be due to lubrication failure (metal to metal contact) at the small ends due to over revving, using 10/40 oil and I suspect excessively high oil temperature. I am reading up on hydrodynamic and boundary lubrication and oil temperature is now my focus (hence fitting a pressure and temp gauge). 20/50 may be enough to make a difference but an oil cooler may be needed if oil is over 80/90°C.

We will see when it goes back together!

[dandywarhol]

Great to hear the bottom end is ok - I was fearing for that to be damaged.

[misterdimwiddy]

Great to hear the bottom end is ok - I was fearing for that to be damaged.

That was my biggest fear!! I would have cried and then broken the lot and sold it if that had been the case.

Just got my skimmed head back which looks lovely; 15 thou still clears the middle inlet valve and will give me 11.85:1. Squish is 48 thou so hoping for no excessive heat build up. £20 cash for the skim at a local work shop and can't fault it. Great bloke too and a workshop crammed with everything mechanical.

He has given me suggestions for where to lose some of the required 40g weight from the JE pistons so may end up doing that.

Rods have gone away for peening (Sandwell UK Ltd) at £65 and barrels dropped off today for rebore.

It's all down hill from here I think. Will be running by January and then out for a winter track day (if they run them) to run it in.

It's gonna fly next summer

[dandywarhol]

I would agree with the weight loss from the pistons - every gramme becomes a helluva lot more at 8000 rpm

[cobbadiggabuddyblooo]

Cool bananas, good news on the bottom end and sounds like you'll be up and running again soon.
I know what I've learnt from this ....
tollerences ......and with the rebuild I'm undertaking I'm finding the more I learn, the more I want to learn.
I will be interested to see how things go on the oil temp/pressure side once you format the gauge setup and have it up and running.
An oil cooler has been on my thoughts for a little while with some of the ambient temps and humidity down here in Oz.

And thanks for tollerating me on my gain for knoweage on your quest..

[misterdimwiddy]

I would agree with the weight loss from the pistons - every gramme becomes a helluva lot more at 8000 rpm

At 8000rpm the piston travels up and down the bore 133 times a second!! With a giant 448g piston the force/stress on the small end journal must be considerable with that level of acceleration/deceleration. No wonder lubrication is critical. It is a miracle that the internal combustion works at all, never mind lasting hundreds of thousands of miles.

[misterdimwiddy]

Cool bananas, good news on the bottom end and sounds like you'll be up and running again soon.
I know what I've learnt from this ....
tollerences ......and with the rebuild I'm undertaking I'm finding the more I learn, the more I want to learn.
I will be interested to see how things go on the oil temp/pressure side once you format the gauge setup and have it up and running.
An oil cooler has been on my thoughts for a little while with some of the ambient temps and humidity down here in Oz.

And thanks for tollerating me on my gain for knoweage on your quest..

It's not a question of me tolerating any comment here and thanks for your input; we all love the TRX in different ways and as a track rider I am keen to understand why the damn thing goes wrong when you tune the motor. The main thing I have learnt is that if you are going to tune a TRX, make sure everything is right.

My hope is that any info I share will be of interest or assistance to others who are striving for more power.

All of the responses here prompt my own thinking and help me to decide where I have gone astray so any comment is welcome.

This time around I think I have got it mostly right and I can't wait to be caning it around various circuits next spring.