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Yes, I agree it looks rich. I haven't done a correctly-performed plug chop but it seems to be a "normal" colour. It was set up on the dyno at a well-known UK Vespa tuner. At a guess it's done maybe 2000km since then. I don't remember the squish but it was within the tolerances on the BGM setup instructions.

Of course, it'll be set up all over again with the rebuild. In the meantime, any tips on how to clean the piston crown?
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Hmmm looks like the dyno didn't work that day… lol

Looks like my first malossi 210 attempt.

Cleaning the piston?

WD-40 and a 3M scouring pad will do the job.
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108 wrote:
Hmmm looks like the dyno didn't work that day
I think you're right!
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I would not worry too much about the jetting if OP is happy with performance and it's not fouling plugs.

Don't forget that the BGM head is inset into the barrel. It's 4mm without a head spacer, and OP is running a spacer, so probably 3mm less squish than you're thinking looking at marks on the inside of the jug.
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chandlerman wrote:
I would not worry too much about the jetting if OP is happy with performance and it's not fouling plugs.

Don't forget that the BGM head is inset into the barrel. It's 4mm without a head spacer, and OP is running a spacer, so probably 3mm less squish than you're thinking looking at marks on the inside of the jug.
Yeah that's what I'm looking at and thinking. You can see the 2 ring marks. And where the cylinder head recesses into the barrel…

Im guessing from the top piston ring to the top of the piston is around 3.5mm.

So that 3.5 + squish is the rest of the space…

That's where I'm thinking is it to spec?
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108 wrote:
Yeah that's what I'm looking at and thinking. You can see the 2 ring marks. And where the cylinder head recesses into the barrel…

Im guessing from the top piston ring to the top of the piston is around 3.5mm.

So that 3.5 + squish is the rest of the space…

That's where I'm thinking is it to spec?
Yup. Part of what I love about the BGM is that is criminally easy to get the squish EXACTLY where you want it, and I've never had a head leak with one.
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"The recommended squish clearance is 1.0mm"
(source attached)
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Guessing it looks larger than 1mm, but educated guess.

Not going down the road of suggesting jetting, but definitely looks rich.
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It could be not rich enough and timing to low. I like the silver patches to be gold coloured. Just the beginning of the gold on the outside TFR.

Some guys say 0.8mm squish on the BGM but not bigger than 1.0mm.

Certainly going to be better to ride after this build.
Silver bits gold preferred
Silver bits gold preferred
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Pretty sure I followed the instructions regarding the squish and timing, but it was 7 years ago so who knows! Anyway, it's a moot point as I'll be rebuilding it with a new crank, carb, exhaust and clutch. Just need the weather to warm up so I can get back in the garage. Thanks for your input guys.
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Btw, on the subject of squish, have there been any developments on the measuring front, or is it still a case of stuffing solder down the spark plug hole?
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norman wrote:
Btw, on the subject of squish, have there been any developments on the measuring front, or is it still a case of stuffing solder down the spark plug hole?
Still solder down the hole so far as I know.

I set my squish to .8mm with my BGM 177's and 60mm cranks.
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I usually measure the squish right after the crank is installed, piston on without circlips and piston rings then close the crankcases without any other parts, stator nuts + 2 bolts, cylinder studs, solder taped down to the piston and cylinder head installed. Turn the crank with the flywheel, then disassemble.

Usually do 2 measures to double check.
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Finally opened the casings today. Looks like last time I made a rookie mistake by "adapting" Vespa gaskets for the reed valve. Oops! I guess that could be the reason why there was so much black goop down the back of the engine. Pic shows old gasket with new (correct reed valve version) laying on top.
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That's a sure-fire recipe for a seize right there.
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I'm surprised the dyno run didn't spot the air leak you would have had… would've been pretty significant.
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Well, he was certainly burning gear oil with the state of that BGM gasket. Also confirms how crappy these gaskets are…
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SaFiS wrote:
Well, he was certainly burning gear oil with the state of that BGM gasket. Also confirms how crappy these gaskets are…
I couldn't agree more on those craptastic BGM gaskets!
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I agree, I'm surprised that the dyno guy didn't spot the leak, even if my rebuild was the culprit. Strange thing is that the scooter was running fine, with no sign of an air leak. If anything, it seemed a bit on the rich side by the state of the plug. On the couple of oil changes I did since that rebuild, I didn't notice anything amiss - roughly the same quarter litre went back in as came out. One thing's certain - it'll be put back together with the correct gasket. Hopefully get the crank removed tomorrow, wish me luck!
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whodatschrome wrote:
I couldn't agree more on those craptastic BGM gaskets!
And they still sell them

Now that they're listing country of origin on their invoices, I'd be curious to know what region of HELL these are coming from!
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Ray8 wrote:
And they still sell them

Now that they're listing country of origin on their invoices, I'd be curious to know what region of HELL these are coming from!
The gasket should be produced by Athena, the Italian company. Their product is pretty universal, the gasket material is the same for a lot of motorcycles.

I'm guessing it's made in India or China where they have operations.

But I think it's just a bad design where the blue bead is pushing the gasket away from the edges.

It either works great, or has a catastrophic failure.

I don't think anyone actually tested it in the real world before it was produced.
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Good news - the crank is out! I don't have the correct extractor tool and as I'll be replacing it anyway, I used The Persuader. I was a bit nervous as, even with quite a bit of heat, it took some fairly heavy whacks to come free.

Anyway, the new bearing is in (went in easily coming straight from the freezer and using a lot of heat on the casing, just a few taps using the old bearing as a drift).

The big seal I got from SC as part of a kit is the metal type, which is the same as the type I removed. However, reading on this forum, it seems that if the casing has a lip machined into it, I should be using the rubber type seal. Whilst I'm keen to press on, would I be better advised to order a rubber seal, or would the metal one (with Loctite) be OK?
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If the casing has a groove machined where the seal goes, it's a rubber seal you'll need.

Even with that, best use a loctite for rubber to metal contact.
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108 wrote:
If the casing has a groove machined where the seal goes, it's a rubber seal you'll need. Even with that, best use a loctite for rubber to metal contact.
Thanks, I'll get one ordered. Whilst having the engine apart, I'm going to change the cruciform. I found a lot of resistance when unscrewing the selector rod (reverse thread) and I'm pretty sure the thread is now mullered (not by me this time!). So rather than trying to force it into the new cruciform, I'll add a new selector rod to the order.
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⬆️    About 3 months elapsed    ⬇️
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It's finally warmed up enough for me to get back in the garage!

I've test-fitted the cylinder with the new crank and I have a question about squish. BGM recommends 0.8 - 1.2mm, but the general opinion amongst learned MVers is that the low end of that range is preferable.

Following advice on this thread, I used a 5mm base packer and a 1.5mm secondary base spacer (no base gasket as such). At the head, I used a 1.5mm spacer and the standard copper gasket. Dry fitting this combination (no piston rings and no gasket sealant but torqued down correctly) didn't make a dent in the 2mm solder stuck across the piston crown.

I removed the 1.5mm head spacer, leaving just the head gasket in place - this gave a squish of 0.7mm. Bearing in mind that this was without gasket sealant which I guess must reduce the squish by a further (small) amount, it seems I need to play around with spacers and gaskets a bit more.

Any advice on which combination to use gratefully appreciated! I have available the following:

Base:
5mm packer
1.5mm & 1.0mm spacers
0.6mm, 0.4mm & 0.2mm gaskets (original set supplied with the kit)

Head:
1.5mm & 1.0mm spacers
0.5mm gasket (original supplied with the kit)

Thanks!
5mm base packer + 1.5mm spacer
5mm base packer + 1.5mm spacer
solder attached to piston crown with grease (using original head gasket here but I will use a new one for final fitting)
solder attached to piston crown with grease (using original head gasket here but I will use a new one for final fitting)
squish measurement 0.7mm
squish measurement 0.7mm
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5mm base packer & 1.5mm base spacer + 0.2mm gasket. BGM 0.5mm head gasket. This will be theoretically 0.9mm and slightly more with base sealer. No sealer on the head or it will make it leak.
Measure the solder at the tip. It will be slightly less.

Bigger issue with the BGM kit is the port timing. Blowdown is low anyway. Adding a long stoke crank makes it even lower. Raising the exhaust port across the full width, between 1mm and 3mm (depending on desired outcome) fixes this.
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Thanks Jack. Is there a particular order I should assemble the base spacers and gasket or is it not important?

Regarding the exhaust port, can I get away without doing anything? I'm not confident enough with the Dremel ...
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norman wrote:
Thanks Jack. Is there a particular order I should assemble the base spacers and gasket or is it not important?

Regarding the exhaust port, can I get away without doing anything? I'm not confident enough with the Dremel ...
Without doing the exhaust port it will still run and ride. Just lower power, peaking at less rpm. With low blowdown they feel really strong mid throttle but when opened up, lack performance.
If you just like to cruise about at 100kmh and not modify the kit, change the packers. Bigger sizes on first is traditional.
5mm + 1.0mm on the base and 1.5mm alone on the head. This will lower the transfers and up the squish to around 1.2mm.
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Thanks again Jack. Just to summarise my riding needs:
Quote:
My riding over there is exclusively 2-up and on twisty, hilly mountain roads mostly around 30mph max. The fastest I ever go is maybe 50 or 55mph, and then for only a very short time. Even with the low gearing, I occasionally need to select first gear on very steep hills.
With this in mind, am I really missing out a lot by not enlarging the exhaust port? I managed to slightly open up the ports on the base area to match the LML casings, but attacking the liner itself might be a recipe for disaster with my clumsy hands! Looking at it, I can't even see how I would get the Dremel inside the barrel to access the port.
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It'll just feel like it's in overrun a little sooner, but still have nice broad power band. The low end power comes by robbing the top end performance.

If you do decide to raise the exhaust, use sanding drums in your Dremel and get a flex shaft for it.
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norman wrote:
Looking at it, I can't even see how I would get the Dremel inside the barrel to access the port.
Go in through the exhaust side (granted you have a small rotary tool not a big one, unless you have a long bit).

It's difficult to attack through the bore side unless you have a 90degree tool.
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108 wrote:
It's difficult to attack through the bore side unless you have a 90degree tool.
I have a 90 degree tool and it's MUCH harder to use successfully for raising the exhaust port. The flex shaft up through the exhaust port is really the only way to go in my opinion.

I would not be in a hurry to start raising the exhaust on the BGM, though.

Part of its appeal is that the power comes in low and stays strong up past 8,500 RPM's. Mine pull wheelies easily, and once you're at speed, you almost never have to downshift on hills, just open the throttle a little bit more and enjoy the ride.
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chandlerman wrote:
I have a 90 degree tool and it's MUCH harder to use successfully for raising the exhaust port. The flex shaft up through the exhaust port is really the only way to go in my opinion.
Using one of these… it's the only way to chamfer the ports on an iron cylinder…
Using one of these… it's the only way to chamfer the ports on an iron cylinder…
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Thanks guys! Given the type of riding I do and my limited Dremelling skills, I'm going to pass on the exhaust port. This project has been dragging on far too long and I can't afford the time or money to get a new barrel if I mess this one up.

Next question (esp. if our resident jetting expert Jack is around): what would be a good basepoint for the carb? To summarise, this is what I have:
BGM 177/187
60mm Mazz bell crank
SI 24/24 with autolube, Boyesen reed & drilled heart filter
Polini box

Hoping to get the motor buttoned up over Easter so if I need some jets I'd better order them now.
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Start with a 140AC/BE4/135MJ

Order a full set of main jets, because what you want to do is start too rich (motor stumbling), then work your way down. You'll most likely wind up at a 128 or 130 main, but this way you'll know.

Have you done a pressure test yet to make sure you have no air leaks?
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Thanks, I'll check if I have those already. I think I have the mains in a set from SC but not sure about the rest.

I've got the elements of a leak test kit on my bench so I'll be assembling it once the motor's back together. Never did one before so fingers crossed.
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norman wrote:
Thanks, I'll check if I have those already. I think I have the mains in a set from SC but not sure about the rest.

I've got the elements of a leak test kit on my bench so I'll be assembling it once the motor's back together. Never did one before so fingers crossed.
Leak tests can be frustrating, but much less frustrating than replacing a seized top end.
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norman wrote:
Thanks again Jack. Just to summarise my riding needs:


With this in mind, am I really missing out a lot by not enlarging the exhaust port? I managed to slightly open up the ports on the base area to match the LML casings, but attacking the liner itself might be a recipe for disaster with my clumsy hands! Looking at it, I can't even see how I would get the Dremel inside the barrel to access the port.
With the 1.5mm packer on the head, as I said, it will suit the unmodified cylinder better. Will go really well even in this lower timing state. Anything up to 100kmh will be really strong. It will do higher speed but will struggle.

Modified it could have another 10bhp in it but would need a bigger carb and a real exhaust. And sounds like something you're not interested in.
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UTC quote
Great, so 5mm + 1.0mm (with sealant) on the base and 1.5mm (without original copper gasket or sealant) on the head.

95% of my riding on this scooter is either around town or on steep, twisty mountain roads, and always with a passenger, so your solution sounds fine. Just the occasional 5 minute blast along a motorway to the next exit if I take a wrong turn somewhere!
@chandlerman avatar
UTC

Lucky
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 79 P200E, 66 Lammy S3
Joined: UTC
Posts: 9935
Location: Nashville

70 Days Since Last Explosion
 
Lucky
@chandlerman avatar
76 Sprint V, 63 GL, 62 VBB, 05 Stella, 66 Smallstate, 79 P200E, 66 Lammy S3
Joined: UTC
Posts: 9935
Location: Nashville

70 Days Since Last Explosion
UTC quote
I use copper spray seal on the head.
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