Modern Vespa

My GTS300 has now done 520 km since I installed the Malossi V4 cylinder, piston and head. It is running beautifully, but it is consuming oil like a two-stroke.

There is not a trace of oil leakage around the engine, no oil in the air filter bubbles, and no sign of oil in the coolant, so the only place it could be going is out the exhaust. On a recent 250 km run it used a full litre of oil. I have switched to 20W50 in the hope that this would help, but it did not.

I know that V4 kits do use a little oil while running in, but this is ridiculous.

Is a broken ring the only possible explanation? I hate the thought of pulling the whole engine out again! How many rings would have to be broken to cause this much leakage without impacting the performance?

Mike

a broken or incorrectly installed oil control ring will show the same symptoms.

the three piece design of the oil control ring makes for easier installation but a higher chance of breakage, incorrect assembly or placement placement when assembling.

with that level of consumption, i'd think that you would be laying down a james bond smoke screen while riding.

have you tried two-stroke plugs?

all kidding aside, the other possibilities are valve seals or guides. but again, you'd be huffing smoke out the exhaust like crazy.

mineral or synth on the break in? did you heat cycle and retorque?

either way, it's looking like you've got the motor boogie ahead of you to get to the bottom of it. at least once you've forged that path the first time it gets easier!

good luck!

-g

I did have a small problem fitting the oil scrapers. The wavy ring that separates them was a fraction too long, and overlapped itself. So I snipped off about 1/16 inch, and all was fine. I made sure all the ring gaps were aligned as per the Malossi instructions.

OK, I guess the next step is to order a new set of rings and gaskets.

Mike

sounds like you've probably identified the culprit...

on the scraper rings did you clock their openings at the same position or did you clock them 120~180 off of each other? the spring/wavy can be a chore to fit, but sometimes will overlap a tiny bit-- it generally locks in, though.

did you check ring end gap on the cylinder and piston side clearance before assembly and install?

sucks that you've got to hustle the motor out again, but at least you're only out some rings and gaskets rather than a whole kit-- or worse...

-g

I fitted the wavy ring first, then couldn't fit both scrapers because the overlap made the groove too tight. With that tiny bit snipped off so that the ends of the wavy ring just met, the scrapers popped into place with no further hassles. I definitely had their gaps 180 degrees apart, with the wavy ring in between at 90 degrees..

I oriented all the rings in their grooves, installed the piston into the base of the cylinder, then slid the cylinder down the studs and connected the piston up to the conrod. Don't know where I could have bust a ring in the process, or mucked up the ring orientation. Faulty ring?

I eyeballed all the ring gaps with the ring in the cylinder. All had enough expansion space - enough space for my fingernail.

yeah that's pretty much SOP on how i do it on the rings, so i'm guessing either excessive side clearance, ring gap or faulty bits.

an unusual failure mode to be certain.

the only other thing i can think of, is maybe you coughed a circlip and it ate up the skirt of the piston and ring lands and/or rings? i mean... it'll still run like that... and i've seen 'em run like that for a long time... *shrugs*

and, i know it shouldn't matter-- in that it has little bearing or affect on the outcome-- but what was your break in procedure and what oil were you using?

it's definitely a bite out of a shit sandwich no matter how you approach it. hopefully it's the last one and not the first!

pull, tear down and report...

-g

I rode it gently for two days, then accelerating briefly up to 80 kph, and three days later I was pushing it up to 110 kph, but not holding the speed constant for any length of time. After a week I was riding it like I stole it, but still not holding high speed for long, or WOT up hills.

Guess that doesn't help not knowing how much I do a day. Anything from 20 to 100 k.

If you are running without a catalytic converter, or if you take it off for test purposes, you should be able to see smoke from burning oil. Short production run alloy castings can also be porous, are there any oil ways in the head that could leak into combustion chamber or into inlet or exhaust tracts?

Bingo. It's not too long, It's extremely difficult to get the piston into the cylinder while the piston is on the connecting rod, so trimming it seems like a good idea. The first time I had this problem, I contacted Malossi and told them the scraper was too long and I needed to trim it. They told me not to. I ended up putting the piston into the cylinder with a ring compressor and oil, and then putting that on the connecting rod.

Da: Me
Inviato: mercoledì 16 dicembre 2015 20.25
A: - Malossi s.p.a.
Oggetto: 3116208 Rings

Hello,

We just got a 3116208 Cylinder kit, and the oil scraper rings are defective. The end of the ring is (too long). Can you send me part 3513917 with my next order?

- Malossi s. p. a. <Cxxxxx> 12/17/15 at 3:13 AM

Hi Me,
they are not defective. This oil scraper ring is high quality Japanese ring (composed of 3 parts) and it is VERY VERY IMPORTANT to fit it properly (even if we know it is not easy fitting) . the most important thing is NOT TO MODIFY IN ANY WAY THE SPRING ... if you do it you will damage it .
3513917 is the kit including the oil scraper ring set . If you have this latter damaged I can send you 1 pcs but it will be exactly the same as the orher.
Please let me know.

Da: me
Inviato: giovedì 17 dicembre 2015 12.25
A: i - Malossi s.p.a.
Oggetto: Re: R: 3116208 Rings

Hello,

The oil scraper ring is the one that won't fit. It doesn't compress..... I will send you photos on Friday.

- Malossi s. p. a. <malossi>
To Me,

In any case please DO NOT MODIFY THE SPRING...,

I am a bit confused. I am talking about the wavy ring that sits between the two scraper rings. I did not modify the scraper rings.

Because the wavy ring overlapped itself for about 2 mm, the scraper rings could not fit into the groove alongside the overlap. The groove is not wide enough to accommodate two scraper rings plus two layers of wavy ring.

What other solution is there? Should I have hammered the scraper rings into the groove? Or should I have squeezed up the waves to make that ring just a tiny fraction fatter to absorb the extra length (easier said than done)?

I cannot see how what I did could cause any problem such as a broken ring.

Mike

If you use a motorcycle ring compressor and a whole lot of oil, it does go in, even though it doesn't seem like it wants to. If you cut it, bad things happen.

That's an affirmative to what Motavista is saying. The oil scraper rings can be difficult to fit and you must use a ring compressor. I've had the same difficulty on several different engine types, in fact, around 2,500 engine units over the years...lol! Yes, I'm not joking, it was my job. DO NOT SHORTEN anything! Compress! It will fit and it will end your oil consumption problem. Just order the new parts you need and get in there.

OK, so the problem is to compress the wavy ring along its length, and I gather the way to do that is to fit the scrapers first, and then install the wavy ring between them. Because of its excessive length, it will protrude a bit, and forcing it in with a ring compressor will cause it to contract lengthwise and expand between the scrapers a bit.

So my mistake was to fit the wavy one first, and because it had enough sideways leeway, it overlapped instead of meeting but-on and compressing.

We live and learn!

Mike

i've always installed the wavy ring first and then the scraper rings after. the wavy ring has kind of a "shelf" or "tab" portion that should go to the rear(?) and then the scraper rings butt up against that in the land area.

i'm very much rings on piston, piston on rod, and then barrel onto the assembly for this type of work. i've found attempting to get the piston into the barrel loose and fiddle about with the circlips while attempting to piece everything together-- piston, barrel, timing chain, gaskets, et al, to be a pain in all nine of my assholes.

no matter how you do it, it's a real cork-soaker of a job.

-g

That's how we always do it too, except after a couple of hours of trying with one of these kits.