OP
UTC

Lurker
SS180/200, Piaggio Purejet NRG, Suzuki DR650
Joined: UTC
Posts: 1
Location: Melbourne, Aus
 
Lurker
SS180/200, Piaggio Purejet NRG, Suzuki DR650
Joined: UTC
Posts: 1
Location: Melbourne, Aus
UTC quote
Hi,

I'm new to the forum.

I'm after some advice on getting my SS180 setup with a Meteor piston. I'm not aware of anyone who's done this that I can refer to so have registered here in hope...

About 5 years back, I needed a rebore and was on 4th oversize. Instead of putting a PX engine in, I scored a new 66.6mm Meteor piston and had my SS180 cylinder bored to accept it, and had the head lightly machined (just around the edge of the squish band). I rode it for a couple of hours, decided I needed to up-gear the bike, and promptly got distracted by other projects.

I've finally come back to it, disassembled it and found scuffing on the piston. I'm guessing that this was caused by the piston over-heating and expanding. I didn't know a lot about engine tuning when I got this done, and was at the mercy of the engineer who did it.

Piston
Speaks for itself...
External inline image provided by member with no explanatory text
External inline image provided by member with no explanatory text

Cylinder
Scoring/marking evident after being bored, couple of hours of riding...
External inline image provided by member with no explanatory text
External inline image provided by member with no explanatory text

None of the ports have been smoothed/tuned, and have edges (not sharp per se, but not smoothed). The MB example had the exhaust and inlet ports opened up. Should I be considering similar?

Head

There was a write-up on the MB Developments site with pictures of someone who did similar. The pics are gone but I have hard copies. Here's the head from that write-up (with a PX piston)
External inline image provided by member with no explanatory text

and mine (squish band barely changed)...
External inline image provided by member with no explanatory text

I don't have the PX piston, but don't expect its crown would be that different to mine. Looking at the notes the engineer made for my head, the compression ratio is 8.5:1!!! Standard for a SS180 is 7.7:1, and that was with leaded fuel. Any ideas on a reasonable target? I think a Rally 200 is 8.2:1. I'm happy to trade some performance for reliability/longevity - I was thinking 7.7:1 - 7.9:1 and running 98RON fuel.

Because the SS180 doesn't have a head gasket, I could add base gaskets, but doubt that's going to get me far. So would I need to have the squish band machined aggressively like the MB Dev example? As these heads are rare, I would like to minimise the risk of going too far.

I was running a #122 main jet at sea level, timing was correct, and had a BP7HS plug (maybe too hot?).

So does it look like my issue is too much compression and do I need to have the head machined further. Any other advice (besides getting a PX engine)?

Thanks,

Lee
@scooter_west avatar
UTC

Sponsor
Joined: UTC
Posts: 4200
Location: San Diego, Ca
 
Sponsor
@scooter_west avatar
Joined: UTC
Posts: 4200
Location: San Diego, Ca
UTC quote
What was the piston to cylinder tolerance when you had it over-bored? It may have just been machined too tight. GS and SS models take a little more clearance than your average motor. I'd say .004" would be good. If it's tighter than 4 thousandths, that could definitely be your issue. Also, get those ports chamfered properly.

If you've upped your compression, you'll need to retard the timing a bit. That can cause issues. Personally, I'd smooth out that squish band a bit. It will lower your compression slightly and likely give a more complete combustion. That shouldn't be causing your light seizing though.
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