1979 Yamaha DT175mx.

[Tinkicker]

Piston ordered.  It was listed as for an NVT Rambler which used the DT175MX motor. 
I have had my eye on it for weeks, it is half the price of one from CMSNL, but knew if I ordered it, I would find bore damage and need a first over.

No box shown, just writing on the top showing yam part number and NVT part number.  I suppose people thought it may not actually be a genuine one and not take the chance.

Always say never miss a chance to educate others with important information they may require to get themselves out of a tight spot in the future.  Someone pipe up and tell us how there is irrefutable evidence that it is a genuine piston and a genuine bargain without a genuine box.


Piston pics

 

 

 

[Tinkicker]

Try again..

Sat on the sofa this morning, sipping my favourite Arabica bean beverage, watching youtube vids and occasionally looking into the conservatory to give the devil bike the stink eye..

I have a couple of hours before my stomach will start growling and insisting on feeding, so I girded my loins, hitched up my pants and went to do battle with lucifers folly.

Engine on bench, ready for further assessment.  Not made my mind up whether to strip it at home or take it into work.

My word, the ally dust got right back into the intake.  Did not expect that.  The reeds stopped it going further.

A right old mess.  Not sure if it will need the crank pressing apart. That is a 0.020" feeler gauge between the thrusts and flywheels. Not sure of the max allowable, something tells me it is 0.015", but I cannot remember exactly after all this time. It looks and feels a lot, but not a lot of rock.  Edit.  It is fine, well within tolerance.
I need to get the crank out to mic up overall flywheel width before deciding on the next course of action.  I need to check it is true in any case.

Little end bearing looks fine, no discolouring or bits of alloy in it.  I have a new one in stock, so it will be discarded in any case.  I will reuse the pin.

The only score on the piston starts well below the rings, so happy to reuse them.

In respect of the new piston arriving, listed for a late 1970s NVT Rambler.  That little bit of knowledge resulted in a £80 saving over buying  from the dealer.  The holed piston was genuine in a yamaha box.  I will gladly do without the box....

Edited January 7 by Tinkicker

[Tinkicker]

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.

[Tinkicker]

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.

[Tinkicker]

Rod kit arrived and I will press the crank back together on monday. It came with a new small end bearing, so I do not have to open the new genuine one. It is the correct, wide shouldered one for the 175.

Piston arrived and is identical in every respect to the old one.

The corrosion pitting on the left shaft has been sealed with loctite shaft repair goop and sanded down to a polished surface. It is no good for running seal lips over, but will ensure the new seal does not get torn on any sharp edges on refitting. The inner lip is well clear of any pitting, which was confined to around the dust seal area.

I ordered the last remaining ballrace in the transmission. 6303z. Felt fine, but for the sake of a fiver, I will replace it. I know that the two needle rollers are in perfect condition and have never corroded as I can see the running surfaces clearly.

So things should start happening next week.

[Tinkicker]

Crank rebuilt and trued without incident.  Well apart from the last millimeter or so when the pin creaked and jumped.
Luckily I already had my feeler gauge in place so it stopped it jumping too far.

It got a sodding good grip on it though.  A moment of consternation when I thought it was stuck solid.  A good clout with the copper freed it though.

Crank trued up easier than I ever had before. Initial set up with square brought 0.05mm.  A tap with a wedge between the flywheels brought it down to 0.01mm.  About time it cut me a bit of slack.

0.01mm runout.  Well within factory tolerance and at the limit of the gauge resolution.  Happy with that.

Other end.  Width turned out to be 55.94mm.  Close enough to 56mm for me.  Esp considering it was a bit chilly in there this morning.

[Tinkicker]

Couple of hours to spare this morning.  Cracked on building the bottom end.
Left case heated to 100C and crank dropped in.  Transmission dropped in next, giving that expensive special output bearing one last glare before left case fitted. 
Even tried the stores manager who orders 100s of bearings a week to see if he had seen a bearing with the same number.  Nope. Out with the bearing books and nothing.   Arm and a leg time..

Cases screwed together, tried the gears and I have a box containing six gears that snick in and out.

Fitted new piston with new small end, new circlips but original rings and pin.  A word of caution when cleaning out a bottom end after a holy piston event.  Even the piston pin had debris down inside its bore.

Bottom end complete.  I will fit the top end tomorrow and leave the outer cases until after the motor is in the frame.

Still need to strip carb, subject it and the intake parts to a warm bath in my ultrasound machine.  Rebuild with genuine std main jet and throw the damnable spurious ebay special one as far as I can over the garden wall into the field behind the house.

Bottom end built.

[Tinkicker]

A couple of hours spare this morning so I thought to build the top end of the motor and stick the carb top parts in my new ultrasonic.
Did the bottom end of the carb yesterday and also rebuilt that this morning.
My old machine was little more than a jewelry cleaner that I used for cleaning watch movement parts.  Carbs were left partially uncovered and needed turning regularly.
New one has plenty enough capacity to dunk carbs easily, even though it is only 3 litre.  It, being the more powerful pro model also has 4x the power of the old one.

Waiting for the machine to reach its set temp.  While waiting I built the top end and carb body.  I was not going to do the cap, but I just wanted to have another play with the machine before tossing out the cleaning fluid.
 

The offending item.  That ebay special jet cost a fiver.  The genuine one from Fowlers cost fifteen quid.  I thought a 130 jet was a 130 jet, was a 130 jet and gave it little thought.  A tenner saved is a lot.
That tenner saving cost me well over a hundred quid to put right the damage that jet caused.
If you take anything from this thread, it is do not skimp on carb jets.  It may well bite you on the ass.

Also got the engine in the frame and the right side of the motor built up.  She has strong compression at the kickstart.  A bit more insurance..that plug is a B9ES. I went for a step cooler since the bike will be ridden pretty much wide open most of the time.  Rural roads, little traffic and 60mph limits round these parts.  I read somewhere that the B8ES is borderline  hot for open highway use.

Sprocket and chain refitted on left side.  Needs carb, left case, exhaust, wiring, tank and seat refitting and she is repaired.
Stomach is growling so I need lunch.  May or may not do a bit more this afternoon.
Also need to remember to bring home the neutral switch from work.  I took it out when warming the cases to drop the new transmission bearings in....and forgot it. 

 

Edit.. Forgot ths is not the original thread.  I decided to change all the bearings in the transmission while I had it apart, so it would not bite me later.  That engine is to all intents, brand new so far as bearings, pistons and seals go.

 

Edited January 21 by Tinkicker

[Tinkicker]

To purloin a phrase from Motley Crue..  Kickstart my Heart.

Carb on, exhaust on, wiring connected, fuel tank plopped on.  Fuel feed connected.  Autolube pump bled.

Ignition on.  Kick.  Kick ring a ding ding.

Ran it long enough to set idle and check autolube pump was stroking.  It was.

Pulled back the pulley to observe max pump stroke output.  Looked like it should from what I remembered from last time I checked this un and the 100 output.  Since I never disturbed the pump or any adjustments, and it is stroking, I will call that ok.  I have no premixed fuel to run it long enough to measure output and I do not want to idle it for a few minutes with just the build lube inside.  Injection pipe refitted and let it warm up for five minutes.

Sounds good and has six in the box.

Just need to fit the carb vent pipework, button down the tank, refit the oil pump cover and generator cover, and she is pretty much ready for a gentle road test.  Piston rings have already been heat cycled and bedded in.

It was pretty smoky in there as the build oil was burned off.
 

[Simon Davey]

Such an interesting project, so close to the end. 

 

[Tinkicker]

It is the end.  It is fully built up and running fine.  Torn between selling it on or keeping it.  It was a dream that became an absolute nightmare.  But that is my life in a nutshell.  I never have an easy run.

 

If I sell it, someone gets a 40 year old bike that is better than new.  If I keep it, no doubt it will continue to give me "challenges".

Edited January 28 by Tinkicker

[Simon Davey]

Thanks for sharing, it's been quite the restoration lesson, mostly "leave it where you found it".   

 

Seriously though, well done, you clearly have "proper" mechanical knowledge and skill. 

[Tinkicker]

Road test time.  Took her out on a run arround the village perimeter.  Probably around three miles.

She pulls fairly strongly through the gears and behaved impeccably.  
She feels different somehow, more refined.  Perhaps now the carb has been put back to stock settings and with genuine parts, the carburation is right.

Although I have not taken her above 5000rpm yet, I can still detect that vibration through the pegs at 5000rpm, but I had a notion as to what it could be over the winter.
I think it is the chain running over the new nylon chain tensioner block.  It has not yet worn enough to allow the chain rollers to glide across it and I am feeling the edges of the sideplates hitting the edge and sliding over the block.
The tensioner arm is bolted to the same frame crossmember that the pegs are fastened to....

Back where she belongs.. On a very chilly day.  My nose has not stopped running yet..

[Hairsy]

Thanks for sharing this project. Entertainment and education - what more could we ask for. Sorry to read of your other frustrations today!