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Thriller's (alfalfa's) rusty old Yamahas


alfalfa

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I recently got the urge to get a bike back in the garage and start enjoying that small bike life again. Was browsing up a storm on FB marketplace, trademe etc but everything seemed to be either too fucked, moonbeams or in the South Island. Sitting on the couch one night with the Mrs I got the notification that a 73' YB125 was closing soon. Had a few bids already but was still only $550 or so. Chucked a bid on, few back and forths with someones autobid "just to see how high it might go" and I ended up winning it for $590. Whoops :lol:. Supposedly a runner, but has been sitting for a while and the key is lost. Has been registered previously but lapsed.

Got in touch with old mate, bike was in Wellington so organised to go down easter friday and pick it up. Borrowed @anglia4's trailer and he decided to come along for the trip too, legend. Early morning hoon down to Welly, bike on the trailer, back to NP by mid afternoon.

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Got it into the garage and started taking it apart to see what is lurking underneath.

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Lots of surface rust

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Grimey build up on autolube pump. Carb looks pretty good inside though?

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Managed to get the exhaust header off without much trouble. Rings and piston looking good to me so I probably wont bother taking the head or jug off for now.

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Things to do:

I have taken the ignition off and given it to the local locksmith to see if he can cut a new key that fits. The petrol cap has a lock on it too so I haven't been able to get inside that yet to see what state its in. I've taken the petcock off and there's no fuel in there so hopefully no holes. My big idea is that the fuel cap and steering lock and helmet lock were all keyed alike to the ignition but just used 2/3 of the 4 pins (or whatever) so if I can get the ignition key cut then I don't need to bang a screwdriver in and wreck the petrol cap. Worst case there seems to be NOS ignitions with keys and petrol caps on ebay indonesia for acceptable $$ so I will get one of them if no bueno with the locksmith. Fingers crossed he can because I don't really want to wait for Garuda Airmail to be able to ride it properly! 

I've got a new battery coming too. This model is electric start too which is lush/not in the spirit of old 2T at all :grin:.

Questions for the hive mind: unsure what I should do (if anything) about the rusty bits. My initial thinking was to do a quick wire brush of all the loose stuff that is out of sight on the frame under the tank, seat etc and then brush on some rust converter to try and slow down/stop whatever is left. Mixed reviews on effectiveness of that stuff though. Would that be worth it or a waste of effort? Better off hitting it with a wire wheel to properly get rid of it then spraycan/brush on some rustkill primer and closest colour matching topcoat?

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Also, here's something weird. When it was last registered, it was as a "1999 YB125 Autolube" :scratch:

1999 is also the year that it was first registered (I think?) based on the little 12/99 on the registration tag.

It's definitely 'in the system' so I'm hoping re-reg shouldn't be too hard. It's got a vin tag and new font white plate.

Has anyone had a go at correcting an incorrect model year like this before? I've heard some chat that a while ago bikes used just be tagged with the year they were first registered rather than their manufacture year? I definitely want to get this on vintage reg if possible!

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"When a vehicle's details are recorded incorrectly on the Motor Vehicle Register (MVR), these can be corrected by sending an Application to Change Vehicle Details (form MR16, available at any New Zealand Transport Agency agent) to the NZTA Most MR16 forms need to be sent with supporting documentation to prove that the information recorded on the MVR is incorrect i.e. if the vehicle model is recorded incorrectly we would require documents from the manufacturer to prove this before a change would be made."

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  • 4 weeks later...
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  • 1 month later...

I’ve been doing a bit of hooning recently, the weather and everything else has been lining up quite nicely. Goes hard (for what it is), and nothing major has broken or stopped working. On a big ride with @anglia4 @Itchybear and Bucket Barry we found a few kms of good gravel. The road tyres that came on it were fine but definitely left me wanting more. The forks also felt a bit shit. I’m not sure if this is because they just are (lol) or if they need some attention. I pulled them off and drained the oil out. Mmmm delicious smelly black fork oil.

The stanchions are mint which is great. I probably should have done seals at the same time but yolo will do them some other time. The service manual asks for SAE10W30. I had some 7.5W Motorex leftover from one of my mountainbikes so 165cc of in that went in each side. Found a steep speedbump and tried to do some jumps to give it a good test. Felt good, a noticeable improvement A+ would pest again.

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In my quest for new tyres I discovered that 3.00-16 is not a common size and I had basically one (expensive!) option that was stocked locally. I emailed the NZ Shinko supplier and they told me if I want some SR241’s in 3.00-16 I would have to get my local store to order a minimum of 5, pay up front and wait 6 months for them to arrive. Thanks but no thanks. I got in touch with mxstore.com.au and they were more than happy to order a pair from their supplier and ship them express to NZ for free. The curse of rubbish NZ suppliers strikes again.

I fitted these myself - I’ve done plenty of MTB tyres but this was my first time on a motorbike. It’s a bit different with the long steel levers and not needing to worry so much about scratching or wrecking the steel rims. All went on ok, it’s much the same process just more aggressive. They look pretty good on there I reckon!

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Took it out for a test hoon on some twisty roads close to home and did some skids in a gravel pit.

Now I just need to find a suitable rear rack or luggage carry system for some overnighters.

Bring on West-Pest ‘23!

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Last ride ended with a few kilometres of state highway to get back into town after some twisties. I was all barred up from the prior hooning so once on the highway I just hit WOT and crouched down into a speed tuck. Coming up to a corner after a pretty long straight section I sat upright and rolled off the throttle to slow down and the little bugger nipped up! It started making a rank noise and rapidly dropping revs, lucky I was covering the clutch so whipped that in straight away and coasted to a stop. Gave it a few minutes to cool down and checked to see if it would turn over with the kickstart. Thankfully it had freed up so kicked it in the guts and rode home much more gingerly. Looking through the exhaust port and there is a definite gark on the piston that wasn’t there before. Guess I’m taking the head off after all…

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Ok so I've got everything apart and am after some advice on next steps. 

Inlet side

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Exhaust side

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I can juuust feel those marks on the cylinder with a fingernail.

Hone cylinder, sand piston marks down and send it? New piston and rings? It's still factory size.

I've got some richer main jets coming. The current main is a #190 and the factory size in the manual is a #210. I had that on the list to change but hadn't quite gotten around to ordering it :oops:

I also need to find a timing dial gauge to check that's in spec. On the last ride I'm sure I heard a rattle at higher rpms in 1st gear that was different to the normal 50 year old 2 stroke noises. Maybe detonating? I haven't touched the timing at all though but I guess it could be,

There are some timing gauges on aliexpress for pretty cheap ($60 or so) - has anyone had any experience with them?   https://www.aliexpress.com/item/1005004098969689.htm

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That doesnt look too bad at all,

I'd just hone the cylinder and biff some new rings at it. If you can get a new piston for not much more, than do that too. I've seen alot worse running fine.

I'd say alot of 2 strokes would look like that if you pulled them down. 

I've heat seized a few bikes before, and just kept riding them with no problems after they had cooled down.
High RPM and closed throttle positions are not ideal for 2 strokes. Best to feather throttle down etc. But yeah, long periods of WOT are also a bit scary. Could be a bit lean and getting a bit hot, but then again, how much WOT are you intending to do. 

Lean condition could be crank seals too? 

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I'd just replace rings as they look like they've lost tension. Hone bore and wet and dry on piston. Do a crosshatch pattern on the piston skirts as it helps retain oil. Also take the carbon buildup off the top of the exhaust port.

Top of piston does look a tad lean. Oil your filter element which will richen it up quite a bit. Timing you should be able to check with a strobe light.

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Cool cool thanks chaps, that's kinda what I was thinking. New piston and rings are only a little bit more expensive than a ring set on ebay so I'll have a look again if there are any better prices otherwise go for that.

Aware of the closed throttle high rpm issues - I always try to roll off slowly and not close all the way. I had also adjusted the autolube pump stroke to deliver a bit more oil than stock at the closed throttle position to keep a bit of extra lube flowing through when it's in that condition.

I might try and make a leakdown tester to check seals.

38 minutes ago, GregT said:

Top of piston does look a tad lean. Oil your filter element which will richen it up quite a bit. Timing you should be able to check with a strobe light.

I had scraped quite a bit of carbon off the top of the piston before I took those photos - it was fairly dark when it came out.

Best photo I took

Will also get in and clean out that port before putting it back together.

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  • 3 months later...

So now that I had the top end apart I figured I might as well get some of the bits tidied up. Took the head, barrel and air cleaner cover pieces to the local vapour blaster to get cleaned up. He did a great job and they came back looking super tidy. My first time having alloy parts vapour blasted and I was really impressed, the finish is ideal for half-assed restos like this where a super shiny or polished finish would look out of place. 

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I took the barrel up to the local kart shop and they spun it up on the hone and cleaned up all the garks. I tidied up the piston myself with sandpaper and got some nice crosshatching back on the skirt so hopefully it holds a bit more of an oil film. Put it all back together with a set of new rings. I also increases the main jet size back to a factory #210 from the #190 that was in there. I have a #200 that I might test out if it's a bit rich but it will probably stay in there forever...

Followed a progressive warm up engine break-in schedule from somewhere online and it seems to be running mint. All ready for 600km of mixed gravel as a shakedown run :iconbiggrin:.

Next on the list was to figure out how I'm gonna carry extra fuel, spares and gear etc on the rapidly approaching Taranaki Tunnel Hunt. I had a blue plastic crate lying around that seemed like a good idea so I fiddled with some cardboard-aided-design to make a rack for it to mount on. Final version feels fairly solid but I'm only like 60% confident it will last the whole ride :grin:. The rack is ok but the crate is quite flexy...

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  • 3 weeks later...

@Berlina96 It's comfortable at 80-85 indicated. I can get it to 95 km/h on the flat if I tuck a bit and really wring its neck.

I think I'm still one size too rich on the main jet as it would previously get to 100 indicated before it seized.

Those speeds are all straight off the speedo - I haven't checked accuracy with a GPS yet.

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