Yamaha TRX850 Enthusiasts Forum

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.



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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!!

[URL=http://s1104.photobucket.com/user/misterdimwiddy/media/Image_1616_zpsc6b6b298.jpg.html]

New pins ordered from TTS who commented that 400 track day miles (since new pins and rods went in) is lot harder on any motor than on the road. Also said that a lot of Yamaha motors suffer small end wear. Told me I should have used Carillo rods with small end bushes that can be changed.

Then moved onto the bores, both of which are scored and show high wear on the thrust faces.



When you pop a top ring in and gaze out of the window through it there is day light between the ring and the liner



So, all is not well. It is still stunningly fast however even with some loss in compression.

My route from here is to use new pins (£63), new rings (£66) and then rebore my spare (stock) barrels to suit the existing JE pistons (which measure up to be 90.9mm OD at the skirt from the original 91mm).

Pleased I did remove the barrels but yet more money pouring into the TRX development fund.

The real worry is have I got an oil pressure/circulation issue that is the ultimate cause? Currently reading about oil tank baffles, temperature/pressure gauges etc etc

TTS advised using 20/50 to keep pressure up (I run with Castrol Power 1 10/40) but overall their view was that it is a long way from the road bike that it once was and that higher wear rates will occur. 400 miles at the redline is asking a lot I suppose.

I have only had one day out with the slipper clutch and it was terrific so I cannot jump ship and get a Superduke just yet.

Give it 2 weeks and I will be reassembling it with a big smile on my face (unless the rods are shot; can't undertake 2 full engine rebuilds in one year)

So in there eyes you will always have an inherent wear problem at the pin. You can buy 2 sets of std rods to the price of one pair of Carillo rods. Either way your going to have to remove the rods to either replace or press new small end bushes Inplace. Do the maths and just place new std rods in. Over reving the std rods stretches the bottom cap so oil pressure is lost and wear is exasibated.
Raising compression also raises the heat that the pistons, valves and combustion chamber and barrells all have to bear. You start to reduce the quench or squish zone and this only aids in more heat and the faster wear on rings and blow by washing valuable oil from the cylinder wall.. There's a reason it's called the quench to aid in cooling.

Look at getting a reusable copper gasket made up and look at keeping your squish no lower than .048". This is another reason I'm outlaying the extra $300 to have the piston crown, valves, combustion chamber and exhaust ports ceramic coated to keep things cooler. This will also aid in stopping the vaporising of the fuel and allowing the optimum fuel/ air mixture to work as it should. Why over rev the bike when your power and torque is not there anyhow. Timing of the spark, Keeping the balance right within the combustion chamber will give you a better balance of useable power over a longer period..

Everything has a boundary ( every action has an equal and opposite reaction as they say) and once you cross one this will begin to react through the chain of supplying the power you are looking for. Remember its only a TRX .. Their strength lay with that strong midrange torque out of the corners and if handling and brakes are sorted you will give most a run for their money in and out of the corners. Let them go buy you on the straight as that old dog TRX will be nipping at their heels again through the next lot of twisties or corners.

Oh Mate.... I'm sorry to be reading that your motor is giving you so many problems. You really don't deserve all the rotten luck you seem to be getting, especially as you go to such lengths to ensure things are done properly.

Thanks though for posting your findings, together with probable causes and remedies. You have added tremendously to the Trx knowledge base and raised issues I would never have considered. Suffice to say I'm now thinking about your issues and how they might affect our motors.

I never ever thought of small end friction issues as part of the Carillo rod debate. It makes sense now it has been mentioned. Were the rods and pins 40,000 miles old at the outset?
One thing I have thought about is cylinder liner wall thickness, or more precisely,lack of when boring to 91mm. I think rigidity and dimensional stability may be being compromised. Although I very much want my engine at or above 900cc for the torque benefits it will bring. I feel new thicker wall liners will be the way to go.

Anyway sorry to hijack your thread. I know you'll you'll find a solution, you always do.

Good luck Pal.

Mark.

edit.
Re-read your post Phil, new rods and pins and 400 track miles later this is the result. I'm shocked that much wear has taken place.

Also look at the design of the JE878 piston and the way the oil is fed to the pin. It relies on a good surface of oil on the bores. The oil rings feed the pin which in itself is a slightly different set up to the std piston which from memory has holes under the piston that feed the pin . I questioned a lot of the designs on both std and JE pistons and there different ring designs to allow for piston rock and oil feed.
Look inside the piston where the pin goes and you will see the galley fed from the holes in the piston at the oil rings. It's crucial to keeping all lubricated and cool. The std trx top ring has a curved face to accommodate piston rock at TDC where as the JE piston has a square faced ring but you will notice a larger gap in the piston where the ring sits to accommodate the piston rock as the ring has enough top and bottom movement to allow for this tollerence .

As Mark said , its a shame you have to go through all this but don't stress, do a little research and look at the limitations and the inherant designs and just work with what you have to get the most out of it and hopefully build a motor that enhances and compliments itself ... And yes Mark I would not be surprised if the bore has something to do with the heat here too.. I'm sure it will all come together with a little time , research and patience... Best of luck with another rebuild ..

Phil, Sorry to hear of your engine woes, but it looks like you know where the oil has been going now.
You have now convinced me. I am not touching my engine i'm just going to ride the pants off it next year
exactly as it is now. Except new (secondhand) supercorsas which i have now ready to fit.
All the best with the build.
Dave

Ough, I just logged in to the forum to see if there are any hints of tolerances to be used with the JE pistons. And see this bad news!
The work shop guy called me, there are no instructions with the pistons how the cilinders should be drilled. Does anybody know this?
And is the correct tolerance used with your cilinders, Mrdimwiddy?

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.

Gents and Ladies, not trying to tell you how to suck eggs .....you just can't rebore a TRX to 878 and hope for the best, The oiling system in the TRX has many small but significant components and as Cobba stated going to 878 requires you to overhaul other components. There is no design flaw in the JE878, they have approached the piston rock in a different manner and oil the gudgeon pin via the scraper oil ring. Things to do and check before striping the engine for a rebuild,

Pistons are not round when cold, they expand and fill the bore when hot, a point to remember when looking at piston and bore wear.

Buy yourself a QUALITY vernier calliper, micrometer, bore gauge and feeler gauge.

measure you oil pressure, hot and cold, idle and mid RPM, is there a significant difference? If so why?
do a (several) leak down test...is it valves or piston leaking? Are the valve stems worn, allowing valve instability?
do a compression test, (dry and wet) do you have a bias to one side due to valves or worn piston/rod assembly?
flush the engine with a high quality oil flush and then replace the oil, recheck the oil pressure, this cleans all the residue from the engine.
Clean the outside of the engine, makes it a hell of a lot easer to strip when clean.

Before/during rebore,
Check the clearance of the oil pumps, remembering that the scavenge pump must be able to pump more fluid than the pressure pump can deliver.
Check that the filter in the rear of the "dry sump" outlet pipe, is clear and free of debris.
Check the oil pump pressure relief valve (seat, ball and spring) is functioning and that the inlet is clear. Replace this valve as a matter of course.
Check that the over pressure valve is working and not held partly open from crap, Replace as a matter of course.

My only concern with the JE pistons is that the Yamaha piston is cooled by oil forced up from the bigend bearing and this oil is then captured buy two oil weep holes that lubricate the pin.
This is not a perfect system BUT under normal conditions works perfectly well.... as the pressure from this hole is subject to overall oil pressure and bigend bearing wear. As the big end wears so the volume and pressure of the oil trying to lubricate/cool the piston and gudgeon pin falls away. Any excess oil will fall to the lower side of the piston and lubricate the barrel wall. Where most of the thrust force is located.

The JE piston reliers on oils being thrown against the bore walls (by the crank/rods) and being caught by the scraper ring, fed through the oil ring then through piston to the gudgeon. Work great with a vertical wet sump engine , BUT if the majority of the oil is falling on the lower side of the bore then this system has some obvious flaws....very little oil is getting to the gudgeon pin The more the pin wears the more the piston rocks and then the bore wears in the thrust region, engine starts to burn excessive oil.....Gents this is the consequence of and action unplanned and ill conceived

You must understand the precept of the concept, of the original action before making any modifications to the design, Rods Rule 1.1

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

coxylaad wrote: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.

Exactly... Here's a perfect analogy. You go to the doctors because your suffering something , they say take two of these 4 times a day. You soon start to have reactions from the medication and they tell you to take 1 of these to counteract this but then you feel tired so they say take one of these with the other lot of medication . The happy pills keep you aware but you suffer moods swings ... Before you know it your have a diet of uppers downers inners and outers.. take 5 minutes to just look at yourself and what may have triggered the problem to start.... Mmmm maybe it was that 10 days on holidays drinking to excess ...

There have been plenty of 878 kitted bikes with stock trx conrods that have no issues after 20-30,000km.. As I mentioned why fork out lots of dollars for Carillo rods when you will still suffer the same problem in there eyes. The problem is not the rods but something else in excess beforehand...

Look at the trx motor to start. It was designed as a dirt bike motor and lower midrange power with the footprint of the 270' crank is perfect for a Paris/ Dakar motor through sand.. Work with the strengths and boundaries that this motor design ultimately dictates and you should have a strong reliable motor.. Just take a few minutes Phil and don't just jump in ..
Look at the yamaha moto GP bikes .. Yes Honda may have more horsepower but the Yamaha has the ability when exiting the corners to get more useable power to the ground earlier .. One of the strengths of the 5valve head is in the lower midrange because of the boundaries dictated overall by the physics of the design itself. Same with the bore and stroke of the trx itself.. Once you look at these boundaries dictated by the design of the product, look at what you choose to do and build the motor in a way that any alteration will complement what your trying to achieve..
I flogged the ring out of my stock trx with FCR's and pipes and it coped really well and at 125,000 km I pulled it apart. I found the rods had suffered oil starvation in the first 50,000 km before I had it and had been rebuilt still with those rods Inplace. But Yamaha new all the boundaries and left enough tollerence to cope for reliability.
Sure it may have a 10.5 :1 compression ratio but the reality comes down to To achieve that 10.5:1 compression when running the fuel air mixture has to be at 100% constantly throughout the rev range to achieve this and the port design, temperature,humidity,density of mixture, the carbs themselves, ECU with emission, noise, fuel octane laws just won't achieve this in reality..
You may do a modification to give you more horsepower but its torque that gets you there and horsepower holds you there.. But you have to get there first. So if you rob from Peter to pay Paul is this ultimately what you want as useable power to do the job at hand...

You'll be right mate just look at what you really want from the bike.. I say all this with the best intentions at heart...

cobbadiggabuddyblooo wrote:

coxylaad wrote: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.

Exactly... Here's a perfect analogy. You go to the doctors because your suffering something , they say take two of these 4 times a day. You soon start to have reactions from the medication and they tell you to take 1 of these to counteract this but then you feel tired so they say take one of these with the other lot of medication . The happy pills keep you aware but you suffer moods swings ... Before you know it your have a diet of uppers downers inners and outers.. take 5 minutes to just look at yourself and what may have triggered the problem to start.... Mmmm maybe it was that 10 days on holidays drinking to excess ... There have been plenty of 878 kitted bikes with stock trx conrods that have no issues after 20-30,000km.. As I mentioned why fork out lots of dollars for Carillo rods when you will still suffer the same problem in there eyes. The problem is not the rods but something else in excess beforehand... Look at the trx motor to start. It was designed as a dirt bike motor and lower midrange power with the footprint of the 270' crank is perfect for a Paris/ Dakar motor through sand.. Work with the strengths and boundaries that this motor design ultimately dictates and you should have a strong reliable motor.. Just take a few minutes Phil and don't just jump in .. Look at the yamaha moto GP bikes .. Yes Honda may have more horsepower but the Yamaha has the ability when exiting the corners to get more useable power to the ground earlier .. One of the strengths of the 5valve head is in the lower midrange because of the boundaries dictated overall by the physics of the design itself. Same with the bore and stroke of the trx itself.. Once you look at these boundaries dictated by the design of the product, look at what you choose to do and build the motor in a way that any alteration will complement what your trying to achieve.. I flogged the ring out of my stock trx with FCR's and pipes and it coped really well and at 125,000 km I pulled it apart. I found the rods had suffered oil starvation in the first 50,000 km before I had it and had been rebuilt still with those rods Inplace. But Yamaha new all the boundaries and left enough tollerence to cope for reliability. Sure it may have a 10.5 :1 compression ratio but the reality comes down to To achieve that 10.5:1 compression when running the fuel air mixture has to be at 100% constantly throughout the rev range to achieve this and the port design, carbs, ECU with emission, noise, fuel octane laws just won't achieve this in reality.. You may do a modification to give you more horsepower but its torque that gets you there and horsepower holds you there.. But you have to get there first. So if you rob from Peter to pay Paul is this ultimately what you want as useable power to do the job at hand... You'll be right mate just look at what you really want from the bike.. I say all this with the best intentions at heart...

ARGH paragraphing please Cobba, this is so hard to read

Tarwetijger wrote:Ough, I just logged in to the forum to see if there are any hints of tolerances to be used with the JE pistons. And see this bad news!
The work shop guy called me, there are no instructions with the pistons how the cilinders should be drilled. Does anybody know this?
And is the correct tolerance used with your cilinders, Mrdimwiddy?

When i did my 878 they had to drill them individual, i got word from JE in the states and the pistons differ a bit (castingprocess according to him). Hence different/individual bore.


Here are the measurements he sent me way back, and also his details.
Now we're talking! You'll want to set piston to cylinder wall clearance at .0030 or .08mm and your top ring gap should be about .015-.016 or .406mm. Good luck!



Tjader (Tj) Harris
Sales and Tech Support
JE Pistons Powersports Division
Direct (714)898-9763 ext.280
Fax (714)379-8213

Thats mobile phones for ya Rod...

On a lighter note, reading this back it sounds like a scripture from the TRX bible from Brother Lee Love.... Hallalooya..
The TRX is just like a religion in itself, And like all religions discipline is involved and with discipline comes respect.. And keep these disciplines within your motorcycle and it will respect you..



I'm hungary now, Hey Janet can I have more of that mushroom tea...

You need the holes in the top of the rods to feed the oil to the pin on the rod itself..

The oil rings scrape the oil and feed it to cool the piston crown and where the pin sits either side in the piston.


and where that feeds the piston crown and pin either side





You can see how the pin is fed oil on the std piston





Note the difference in design also with the JE piston having a full skirt compared to the std piston on the bottom and extra weight

Also note the difference in the pin itself with the JE pin being around twice the weight of the std pin.



So your carrying a lot more weight with the JE pistons especially around the pin. If you want a little more of that midrange punch out of the corners this is one of the reasons why the Yamaha OEM piston has a lighter pin and skirt design.

Thats why if you get the pistons and pins back to the OEM weights your complimenting one of the parameters of the original design.

This may only have a detrimental 3 or 4% gain to that midrange punch but you find these couple of things here and there, like if you have Kent cams then again will complement what your asking of your motor. 3 or 4% of that midrange horsepower is 2 or 3 extra ponies at 5500rpm or maybe 5hp with the kent cams..

You can find so many more gains with timing and spark and just getting your fuel air mix right that will compliment everything if budjet is an issue than looking for overall compression because if you go down this path you will have to adress all these issues to make it work to it's optimum anyhow.
These are all just basic dynamics to the internal combustion motor anyhow.
If your spark is too far advanced or retarded through certain parts of the rev range your at a loss and your starting to lose that 3 or 5hp gains from balaning the piston weights and cam timing.
So much can be gained from a good full strong spark. If you have that right air/fuel more gains as your burning all your fuel, more power gains.

Time for more mushroom tea...

cobbadiggabuddyblooo wrote: You can see how the pin is fed oil on the std piston

Mate they're outlet hole on the underside of the piston, the oil to the piston gudgeon is feed along the pin its self