Over a Barrel (BGM187)
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Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Mon Oct 28, 2019 3:04 am quote
List of jobs seems neverending but it is getting there. All looking really good. Don't care for the air delflector. It won't do much and will likely end up wrapped around the fan at some point.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Mon Oct 28, 2019 11:53 am quote
Cheers Jack, it feels more like I'm running out of jobs, and don't want to finish so soon; it definitely isn't going in the frame over winter.
I might have to give 'Old Faithful' a little top-end-only tweak too, I have the Dremel warmed-up, and the spare skimmed head I replaced with the Malossi one.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Thu Oct 31, 2019 1:11 pm quote
Who uses Dirko, or anything similar on the main casings/gasket?

https://www.ebay.co.uk/itm/Dirko-Grey-silicone-Elring-Sealing-Compound-70ml/202661025192

I've only ever used grease before, with a proper thick green Piaggio gasket, thinking that anything else was only necessary for knackered casing surfaces, but whilst searching for a video I was sure I'd seen where FMP did a JB Weld repair to the thin gasket area of the oil sucker problem, I saw that in fact it was this Dirko Grey that he uses. I'm in three minds (I used to be indecisive, but now I'm not so sure):
1) A thin JB weld job, but will the gears eat it without harm if it comes loose?
2) FMP's Dirko Grey on the fly-side casing, and built-up under the thin oil sucker area, if so I'll get some. (as video linked below).
3) Stick to just using grease because my mating surfaces are fine, and this has not been a problem before.

FMP's video:
.
“https://www.youtube.com/watch?v=Yjxk4StYH7w“

Also, in case anyone is interested, I made a CHT sensor from a thermistor, to fit into the M10x1mm threaded pocket in the BGM head and the TrailTech extension lead plug that is wired through my scooter to the gauge up by my speedo. I've tested these thermistors before alongside a TrailTech sensor, as well as checking the specification with as much info as TrailTech publish, and they read the same as the TrailTech ones. I've been using a home-made thermistor sensor on my engine for a good few years now, and I can just plug this one in instead:

https://www.ebay.co.uk/itm/Thermistor-100k-Ohm-NTC-EPCOS-B57560G104F-Temperature-3D-Printer-RepRap-Prusa/262457986447

The next big job really is bearings, but I'm leaving the old ones in until after a final attempt at having the stuck engine bolt removed, so I'm just clearing these few odds and sod jobs first, so I'll be ready for the final push when the urge strikes.......

Oil Sucker Area - does anyone bother with it.jpg

BGM TrailTech Thermistor CHT Sensor.jpg

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7101
Location: Victoria, Australia
Thu Oct 31, 2019 5:45 pm quote
sime66 wrote:
Also, in case anyone is interested, I made a CHT sensor from a thermistor, to fit into the M10x1mm threaded pocket in the BGM head and the TrailTech extension lead plug that is wired through my scooter to the gauge up by my speedo. I've tested these thermistors before alongside a TrailTech sensor, as well as checking the specification with as much info as TrailTech publish, and they read the same as the TrailTech ones. I've been using a home-made thermistor sensor on my engine for a good few years now, and I can just plug this one in instead:

https://www.ebay.co.uk/itm/Thermistor-100k-Ohm-NTC-EPCOS-B57560G104F-Temperature-3D-Printer-RepRap-Prusa/262457986447
So does the thermistor sit loose inside the copper pipe? Or held in there with what looks like JBweld? Could it be used with a spark plug ring (like you get with the TTO gauge)?

I use Threebond (aka Yamabond, Hondabond etc) for case closing. Got sick of thinking "it's probably not leaking..."
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Thu Oct 31, 2019 11:38 pm quote
Hi Ginch, I coat the wires and fill the tube with JB weld first, so it's all held solid in place, the thermistor is right at the tip, but protected. I suppose you could use a proper high temp potting compound, but JB was to hand as always, and doesn't conduct electricity, so seems perfect for the job. The first one I made was with the old hollowed-out TTO spark plug ring, after it had failed, which TrailTech replaced foc; but I had the ring, lead and plug, so for £1 for a thermistor thought I'd remake it and compare new with home-made, and haven't bought a £30 sensor since. It's actually more hard-wearing with the layers of heat-shrink, which helps around the spark plug. I've made them for cylinder studs too, using a large electrical spade connector.
I see Yammabond Threebond; looks to be the same sort of product. I'm not really keen on having it all over my casings, but, like you, I'd like to know that I'd done everything to prevent the oil-sucker issue, so think I'll do it this time round.
Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7101
Location: Victoria, Australia
Fri Nov 01, 2019 2:34 am quote
Cheers Sime, I'll give it a go as I have a few rings that have given up the ghost. Just to be clear, is it important that the thermistor doesn't make actual contact with the copper?
Yes the heat shrink helps in another way too, and that's to ensure that the only part doing the temperature reading is the actual part in contact, not the bit up in the breeze from the fan. Makes a measurable difference.

The threebond will clean up easily with acetone (I think) if you get to it quickly - it skins over fast. But it's very messy shit! And doesn't come with a nozzle, at least the ones I've bought don't.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Fri Nov 01, 2019 3:33 am quote
A thermistor is different to a thermocouple; it all goes on in that tiny glass end bubble with micro-variations in resistance, which are read at the gauge. The isolation (JB Weld or potting compound) is just to protect it from impact and vibration. I think even the wire tails are coated and don't need to be isolated, though I did with the first one I made – (below), but I've found that they need stripping (I use a scalpel) of any coating at the ends before soldering to the leads, then they need isolating; more heat shrink.
I'll dig out the precise reference for the ones I actually bought if I can find it back in my Ebay orders; it's important to make sure you have the correct temp-range (-50 - 260°C) – they seem to be intended for 3D printers. The point is they cost pennies, so you might as well have a go if, like me, you have old ones lying around; it was a bit might-as-well trial-and-error before chucking the old one out, but it works.

Found them; they were '100K NTC 3950' – 3950 is the 'B' value, whatever that is; it's stated in the table on the link above, and 100k(ohm) is the resistance; it's all a bit cloudy in my memory, and one lot I bought from China and they were really cheap, but those are the figures to check before ordering.

Here's the first spark plug one I did; note I tried to isolate the tails but think it isn't necessary, and you can't get the solder joins into the copper sleeve, so lots of layers of heat-shrink, which I took right down, so the copper of the ring tube wasn't in the air.

100K NTC 3950.jpg

cht ring thermistor replacement.jpg
First one, with old TTO ring.

Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Fri Nov 01, 2019 3:37 am quote
I've had a few of those oil suckers before. Using any old rtv sealer and fitting the gasket on the flywheel side first, seems to have the most chance of success for me. Will show up in the pressure test but hate taking them apart for a 2nd go. Wish I was putting mine together sometime soon, could be snow on the ground before the neighbours start wishing it was still in pieces.

Can you not fit the plug in the centre of that BGM head and sensor in the side hole? this would surely make more power.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Fri Nov 01, 2019 4:16 am quote
Hi Jack; I do put the gasket on the fly-side, and I'm going to do FMP's oil sucker preemptive mod; be silly not to now I'm aware of it.
The pocket for the sensor is M10 and not full-depth; it's into the meat of the head above the spark plug, so swapping them wouldn't be at all simple, especially with a big hole where the spark plug was, and it's a long reach plug, which goes into the centre of the combustion chamber.
It's a shame you were held up with the dodgy order, I wasn't at all impressed with SC this time either; their pre-order technical replies were lazy, their order processing was slow with different excuses contradicting each other, and the order accuracy and quality was disappointing, so I re-bought a few bits from Wasp in UK, rather than bothering to complain or return, but I'll be back to SIP next time.
Any snow will be well and truly thawed and it'll be daffodils and Easter bunnies before I'm rolling around outside in the car park fitting this engine, so you'll still be done before me, as will all our Californian chums, and of course it's spring down-under, which is where I'll be re-emigrating to if the UK gives Cummings's gang any majority, so I'm not making any long-term plans here.

BGM177_8-016.jpg

Veni, Vidi, Posti
74 Super, 75 Super, PX project, LML off-roader and new to 2018, '66 Blue Badge Smallframe
Joined: 30 Nov 2011
Posts: 7101
Location: Victoria, Australia
Fri Nov 01, 2019 12:22 pm quote
Cheers for that Sime, the pictures make it nice and clear!

Jack there was somebody (I'm thinking Polini but could be wrong) that was making a head with 2 options for plug location... just can't recall what cylinder it was for.

Sime where did you live when you were here last?
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Fri Nov 01, 2019 2:37 pm quote
Ginch, it wasn't Oz; I followed a girl to NZ in 1995, got a work permit under the points system, then permanent residency after two years, and full NZ citizenship after five. I haven't been back for a long time though, and understand it's very different now, but still harbour dreams of moving back one day, especially since UK went mad.

Anyway, this evening's little project, while I'm procrastinating about what really needs doing, and still on the home-made kick, I dug out my crank test jig that I made a few years ago and have hardly used since, and gave it a spin; this crank having arrived in a beat-up box and having since been cut and had the fly-side inner race fitted by my own clumsy hands, I thought it was worth checking. It is remarkably straight, registering almost zero, certainly less than 0.01mm at the three test points, where 0.02 or 0.03mm is admissible. So, as I'll be pulling it onto the bearing, rather than tapping it, I know it was straight before the engine ran (before Mazz's "inevitable" breaking!)

Quick Video:

.
“https://youtu.be/uzt5Yucs6iQ”

31458238045_3bf32aa832_b.jpg
'Admissible' run-out

Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Fri Nov 01, 2019 7:35 pm quote
Ginch wrote:
Cheers for that Sime, the pictures make it nice and clear!

Jack there was somebody (I'm thinking Polini but could be wrong) that was making a head with 2 options for plug location... just can't recall what cylinder it was for.

Sime where did you live when you were here last?
I thought it was that one but clearly not. Sure its possible to do though. I wonder if running two spark plugs would up the torque by enough to notice. They do it on 4 strokes. Would make an interesting experiment.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Sat Nov 02, 2019 1:46 pm quote
Twin-spark Polini 178-187cc kit for Vespa PX:
https://scooterlab.uk/twin-spark-polini-178-187cc-kit-for-vespa-px-component-news/

Also just stumbled on this one on Ebay, and that Scooterlab write-up says something about offset spark plugs were usually used in conjunction with offset squish heads in order to help the wider squish section cool the exhaust side of the piston, so an older one, for a different reason?:

PM tuning Twin Plug Head:
https://www.ebay.co.uk/itm/Vespa-PM-tuning-Twin-Plug-Head-80s-Px125/123862738693
Molto Verboso
PX221 Malossi, O tuned PX200 and some motorbikes
Joined: 14 Jun 2017
Posts: 1557
Location: London UK
Sat Nov 02, 2019 7:22 pm quote
Seeing as this has been around since the 80s and never caught on, it must be garbage. So back to plan A.

Well done for clearing up that it was Polini. I think I have thought that it was BGM before.
Hooked
1984 PX(177)EFL
Joined: 14 Apr 2017
Posts: 201
Location: Cornwall UK
Fri Nov 08, 2019 7:09 am quote
Had a play date with New Best Friend this morning; only £30 for shiny casings, which serves no purpose but makes me happy and keeps him sweet for future jobs. The stuck long stud stayed put though; mainly because I was too timid to have it buggered up (it's basically encased in 40yo concrete inside the arm); the threads are freshly-recut though and it will go again.
Anyway, now I'm ready for next push, roughly as follows:

Remove old bearings and seals.
Fit new bearings.
Get main bearing and crank aligned with inlet pad.
Fit new silent blocks.
Fit seals and 'o' rings.
Check PBT, squish etc., finalise head gasket(s).
Double-check all calcs, including remeasure of head volume, but not too stressed about it.
Dry-build gearbox, check/correct alignment/shims.
FMP's oil sucker pre-emptive work; I have Dirko Grey now.
Casings together.
Cylinder studs, piston, rings, cylinder and head.
Pressure Test.
Carb box, carb, Patrick's Bellmouth, best guess jetting if any suggestions.


That's it; no hurry, should all be tidied away before I box up my freight for the exodus.

shiny.jpg
Missed a few crevices, but only £30

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