A few beers and a good nights sleep later, I resolved to grab the devil bike by its evil little handlebars and set to disembowelling it.
So first things first.  Drain the transmission.  What a stupid long drain plug thread that is.  It looks like it could almost bolt the tank on.  Ridiculous, but then I guess they did not want ham fisted owners stripping the thread.
​​​​​​
Plug out and viewing the flowing oil with a faint feeling of dread.  Will I find the shiny particles of death making pretty swirling patterns in the oil, or worst still, bigger chunks?

Thankfully nothing in the oil, it was relatively clean.  Just a few hundred miles of general friction plate dust discolouring it slightly.
​​​​​​
Kickstart lever, shaft protector collar and seal protector shim off , followed by the oil pipes and tach cable. Clutch cover removed.

I was not wanting to see three things, but I had a prefered order of not wanting to see them.

1.  Clutch centre nut loose.  Not a big deal to repair,  but embarrassing as hell to have to relate my incompetence on here afterwards.

2. Clutch basket rivets come loose.  If the basket rivet holes have ovalled, then the basket is trash.

3.  Destroyed input shaft bearing.  I do not even want to go there.

Oil is OK.  No metal in it.  An encouraging sign.


Clutch plates out.  Nothing wrong there.  Clutch nut is tight and locking tab is secure.  I so wanted it to be loose...


Around 2mm slop between primary gear and basket.  When I built the motor there was none.  What is going on.  The rivets are not loose...  Happily the shaft bearing looks to be ok.


​​​​​​Why does it have slop now?  I have seen some clutch baskets on larger bikes have anti shock springs in the primary gear, but this is not the case here.  Why has it got free movement?  It was not something I ever gave any thought to at all previously.  I just assumed there was just a usual small amount of play between the rivets and the clutch boss and excessive play was loose rivets.

A quick look on the internet revealed that the DT175 clutch basket has damping rubbers between the clutch boss and the primary gear.  Well I never.  You learn something new every day.

I found references on how to replace these worn rubbers, but they are not supplied separate by Yamaha.  The basket is a sealed unit. 
It looked like a NOS clutch basket from the US was on the cards, but after several hours of tracking down and finding obscure references and pics of the rubbers in the hope that they were used as a maybe a fuel tank damping rubber elsewhere on a Yamaha and I could identify it.
I came across a company in Germany, quite by accident during my searching, that had replacements manufactured and were selling them.  Duly ordered.  Expensive, but cheaper than a NOS  basket.

I mentioned before that this has been a horrendous merry go round of anguish, but karma is watching and long discontinued and rare parts in new, or pretty much as new condition, have suddenly made themselves available at the exact time I needed them.  Take the exhaust.  It was not pretty and I was constantly searching for a better replacement.
The very day it blew itself apart and I really, really needed one, a new advert appeared on ebay with one in almost new condition.

Seemed a shame to junk my basket as the bike had done less than 2000 miles and the basket was otherwise unworn.
I think the rubbers had hardened over time and the newly applied power and heat in the clutch had compressed them, and having much reduced elasticity, they failed to resume their original dimensions.

And no, I did not identify anywhere that the rubbers had been utilised elsewhere.  Clutch basket only.

I could strip the basket at home.  Drill out the rivets by hand, tap a thread in the basket fingers to accept a bolt and reassemble.  Or I could wait till Monday and having access to a largish machine shop at work and a small team of excellent machinists, get them to do it for me with far higher precision.

I recall they highly prize Jaffa Cakes with their breaktime teas and coffees.  When word gets out that a packet of Jaffa cakes is in the building, the machinists leave no bolt, bearing or cover plate unturned until they have located and raided the packet.

Packet of Jaffas duly purchased in readiness.

 

I'm gettin rite confused. Is this whats going on Now? or are you going over everything you did to get it good--bettter than good!!.
Sorry, brain fade for me, not up to speed.
But just thinking if & when you get it all sorted--what are ya going to do then!!.
Love your work & dedication to get the job done i must say.

Naw, at this point i am reglossing the two stroke paranoia thread for continuity.  Only this time, rather than keeping it strictly technical, it deals with what was actually screwing with my head.

FYI.  Spoiler alert for your eyes only RT.  At this moment in time as I write this, the bike is complete, looks and behaves like one fresh from a dealers showroom back in 1979.

Don't tell anyone..

Well damn, corn nuts back in the package… I really enjoy the roller coaster ride of the story…
Sneezles61

Its possible to make your own clutch shock rubbers, using 2 part PU material. Far more durable than OE, and the PU can be used for making any sort of rubber part, if a mould can be made to do the job.

I take the basket into work and armed with a pack of Jaffas enter the machine shop.
Instant interest from the lads and one by one they sidle over, with one eye on the pack and the other on me.
I explain what I needed doing and thought that maybe the rear cover plate holes should be countersunk and csk bolts fitted instead of the low dome heads supplied in the kit to better keep the plate aligned and in balance.

I was given the look. You know the one, the one with one eye closed as if assessing if you are being serious.
It was pointed out that as the plate was going to have to be drilled out from 5mm (5mm rivets) to 6mm to accomodate the new bolts, it was better from a balance and alignment point of view to remove as little material as possible and to ream the holes to very very slightly larger than the diameter of bolt.
I was then told I would be more gainfully employed by making the tea and coffee to go with the Jaffas, while the misters did the work.

10 minutes later I was back with the beverages and the rivets were drilled out, the threads were tapped and the cover plate was getting reamed to size with a tapered reamer. Took some doing because inexplicably, the plate was hardened steel. They burned out a 5.5mm cobalt drill bit on the first hole and ended up having to use a carbide bit before finishing with the reamer.
Glad I did not try it at home with hand drill now.

In case you were wondering what it looks like in the basket.. I never knew those rubbers existed.

Bare basket with new holes tapped and ready.


Basket with (old) rubbers fitted. I fitted the new ones and reassembled the basket at home.
I work for a very accomodating company who really value their workforce, most often turning a blind eye to "home jobs" shennanigans during quiet periods, but I had burned up enough company time that day and the bearing I was stuck for had arrived.
Reassembling it in works time would have been taking the piss.


And primary gear fitted onto the rubbers. The new rubbers were a very tight fit in the chambers, whearas the old ones in the pic have clearly shrunk and are a very loose fit.

The three small holes in the primary gear housed rubber "pegs" sandwiched between the cover plate and the basket.
I think the purpose of these pegs were to dampen any chatter between the gear and the basket, much like the large O ring did on earlier models.
They had flattened or worn, so I just cut new ones to an appropriate length with about 2mm of compression from 8.3mm nitrile rubber O ring stock. Fitted a treat.


Built the bike back up, took it into the yard and fired her up. No sound from the transmission with clutch pulled or otherwise, just the slight whir and chatter of the transmission gear teeth responding to the firing impulses at low idle speed.

Just need the rain to go away before I can test ride it.

Curious if you would mind sharing the contact information of the company that sells the damper inserts?

Business details

Business name: Michael Dörr - MikePowerParts
First name: Michael
Surname: Dörr
Address: Saarwellinger Str.3,
66822 Lebach,
Germany
Phone number: 068389759111
Email: This email address is being protected from spambots. You need JavaScript enabled to view it.

I found him on the German EBay site.

Item number 334625810866

When the rubbers age and play occurs, the clutch drum drive pegs close to the rivet holes often crack. It's not a great idea to weaken the drive pegs by threading them, as this greatly increases the chances of cracking, so best to use rivets, which are easily available and can be set with simple hand tools.

Clutch basket and drive gear, make a perfect mould to produce PU shock rubbers. Just apply release agent, and pour the rubber. PU is more durable than rubber, and will last pretty much forever.

Thank you Tinkicker!