Just another engine man cutting through the internet bullshit Paul.  Your liner got rid of the excessive heat just fine.  No damage.

Different end of the spectrum to yours, but the principles and physics are exactly the same.

I've see a yamaha 175 head with combustion chamber offset to the rear rather than central. Am i dreaming. Would it be like that to keep the heat away from the exhaust side--if i'm not dreaming haha.

Well the motor is apart.  I made a mistake in thinking to split it at home, wipe out the crankcase, refit the crank and screw it back together again.  It made a 30 minute job a lot harder and longer than it need be due to my completely inadequate home tools. Should have taken it in to work to split.

For the want of some correct sized circlip pliers, a copper hammer and other bibs n bobs I left armageddon in my wake.

​​​​​I am going to have to change the crank seals yet again because it left the left hand bearing in the case when I drove out the crank.  As ever, this sodding bike is going to make me jump through hoops.
I never knew a more recalcitrant machine in my entire life.

I have left an assortment of bent kick idler circlips, part rounded off crankcase screws and even a bruised gen rotor nut when my polyurethene hammer was not man enough to get the crank out of the left case and I lost my rag with it and got all medieval on its ass with a steel hammer.

I should have walked away and taken it into work tomorrow to tap out with my copper.. But no.  A case of a red face  and " I have had enough of you yer fecking bike, you are coming out yer bstard".  I may even have bent the thread on the crank a bit more than it was, so it is going to have to go into work for straightening once and for all,  and the crank checked for true.  I am ashamed....
May as well press the crank apart and check the pin and bearing properly now it is going into work tomorrow.

Of course, we all know what I will find... Rust pits and skidding ridges on the pin most likely.  Its the only part that has not had attention after its 40 year sleep.

I see a ProX conrod kit looming...  Or the crank getting thrown through a window into the canal.  No point fitting a double lip IT175 seal on the gen side anymore.  After checking the new seal path marks left on the shaft, there is corrosion pitting right where the outer lip runs.

Mind made up.   I will get it right and its outta here.  I'm obviously not meant to have it.  I need room for another project.  Something I can ride without devaluing it.

I would pull the crank and take a look at the big end / crank pin.

If you are looking at a new road kit, note the Prox rod is just the same as the "long made in japan" one

www.pjme.co.uk/acatalog/Yamaha-DT175-Con...d--9646.html#SID=898

Isn’t there a RT1 for sale close by? To replace… Lucifer? (:
Sneezles61

Thanks for the tip Paul.  Rod kit ordered. 

By now as everyone will have guessed, I split the crank and it was not a happy clappy time.

As I forecast, rod, pin and bearing rollers were corrosion pitted and the rollers were showing signs of skidding.

Oh well.  Entirely my fault.  I should have checked them when I had the engine apart back in 2021.
They felt absolutely fine and still do.  I relied on it having done less than 2000 miles from new.
Maybe the skidding rollers were the cause of the vibration I felt above 5000 rpm.

Apart from the bearings submerged under oil in the tranny and the clutch bush, that big end is officially the last bearing or bush that has not been changed on the entire bike.  Everything is new.

Not something I expected to be doing when I bought a "fully overhauled" bike from a college motor vehicle lecturer.

Good job I split the crank to check.  That big end did not have 500 miles left in it.

Seal paths evident on crank.  Outside lip of IT175 seal fitted was directly over  the corrosion pitting.  The inner lip is clear and clean.  No point in fitting another IT seal.  It will just wear and blow through.  I have ordered a standard genuine one.


Some rollers were in a dreadful condition.


Pitted pin...


Pitted rod on bearing running surface.


At least I managed to get the flywheels prepped for reassembly and the misaligned thread trued up.


​​​​​



 

Thank you for showing this.  I've learned if there is any chance of corrosion it's best to split the crank no matter how little play or how smooth it feels.  Any trace of rust at all quickly destroys the big end when running.

One the seal...  make sure the single lip seal doesn't ride there... the only proper seal lip will be on the "outside".  Might be worth having the surface reconditioned now that it's apart or a speedi-sleeve installed after assembly but before seal installation? 

So bits ordered...

Kick idler circlips that I butchered. ( correct sized pliers ordered for refitting - do not like bringing my work tools home, I invariably urgently need them for a job as soon as they are at home).
Gen rotor nut. ( Butchered in a fit of angst)
Crank seals.
Rod kit.
2x case screws.

Also got a koyo NR6304 bearing on order for the tranny output shaft.  It feels and looks fine, but of all the bearings in the transmission, it is that one that would be most susceptible to hidden corrosion, being only protected by the oil seal and can only be changed by splitting the cases.

A bit of deliberation.  A B9ES plug.  The roads around here are all rural 60mph limits with little traffic.  That means the bike is pretty much close to wide open most of the time.  The largest town near here would be considered very small by most peoples standards and the next largest is just an overgrown village.  My own village takes five minutes to walk from one end to the other.  So very little low speed  town work.
In view of this I consider a grade cooler plug to be added insurance, along with the standard, genuine mik main jet.
 

Be cautious on the trans output shaft bearing.  It is designated "NX2".  The N is for the snap ring.  The X2 is for a special radius on the outer race and a standard bearing may not press into the case all the way. 

 

Nice heads up mark.  Yes if the bearing is a different radius on the outside, it could cause problems.  I will take a very careful look, but I already know you are right.

For others looking in, why would yamaha make a bearing that is only a yamaha part and not an ISO bearing?
​​​​​​profiteering?  Nah a stock ISO bearing is far cheaper than a bespoke bearing, even for a large company like yamaha.

Yamahaha probably specified the original ISO bearing and upon testing , found the crankcase cracking around it.  So to rectify it, they needed more strength from the crankcase.  At this date, they needed a better profile on the crankcase output bearing housing to give it more strength.  The only way to achieve this within the already settled dimensions was to take a little from the bearing and add it to the crankcase...At a significant cost in bearing purchase..

Tldr. Yamaha do not make bearings bespoke to make them more expensive to you, twenty years later.  Twenty years later means ninety five percent of the production has been scrapped.  Of the the remainer, 40 of the original needs a new output bearing.   A new yamaha bearing costs £30.  A new ISO bearing costs £10.   So Yamaha has the potential to make £800 in twenty years.  Why would they that?

Very simply, a necessity to put right a problem in the very late stage of pre production.  It is not a way of scalping its oily covdralled customers.