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Post by Karl on Aug 13, 2008 15:59:24 GMT -5
My original piston has 2 compression rings, no oil ring.
In the kit I got, the piston has 2 ring slots but came with 3 rings.....2 compression and an oil ring.
My question is, do I use the oil ring or not? The kit came with no instructions.
It's been a while since I've done a rebuild and I don't remember where the oil ring goes. I searched and searched online and found nothing so I'm wondering if this is a generic 47mm ring set for both 2 and 4 strokes and for the 4 stroke the oil ring is used and for the 2 strokes it isn't.
Thoughts?
Karl
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Post by 90GTVert on Aug 13, 2008 17:35:09 GMT -5
I sent this to your email, but I'll post here as well...
A wavy ring is usually an oil control ring, or rather part of an oil control ring. A proper oil control ring should have 3 parts, 2 thin rings with the spring (wavy) ring in the center of them.
I haven't seen the minarelli engine use an oil control ring, after all theres no oil in the crankcase to control. As long as your piston only has 2 grooves for rings, I'd leave that out. Make sure the rings you have aren't way too thin for the ring lands just incase someone mistakenly sent you an oil control ring and not what you need. If they are part of an oil control ring, they will be very thin since all thre parts must fit the ring land. Don't forget to place the dots on the piston rings toward the top.
Torque on the heads should be 11-13 ft/lb. It's not specified, but I like to do this in increments. I put em all on hand tight, then barely snug with a ratchet, then say 8 ft/lb, then your final number. That's more common for larger engines than small, but it really doesnt take much time to ensure everything is seating more even etc... I also recommend using a little 30W oil on the threads to assure more accurate specs. There's a specific pattern they want you to use (which I don't remember), I just do it in a criss-cross manner and it seems to work fine, for example...
1 4
3 2
Hopefully that makes sense.
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Post by kevinx on Aug 13, 2008 19:07:27 GMT -5
What should you use to lube the piston bearing before installing the piston also shouldn't you coat the cylinder bore with 2 cycle oil before inserting the piston
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Post by Karl on Aug 13, 2008 19:11:56 GMT -5
Brent, just getting to you on this and I did respond to your email, thanks, man. That's what I figured, too. I guessed that the ring package could have been for any 50cc engine, either 2 or 4 stroke and that the oil control ring would be sandwiched between the two rings on one ring land, and there would have been another set for the other ring land. It's all put back together and started right up. I do need to jet it correctly but I'm waiting on those parts to come in. Should be here by the weekend. I've got a little bog/hesitation at about 1/4 throttle. I had the jet needle clip at one setting below middle or 2nd from the bottom, but I put it back to stock. It still has the bog. I bought 4 jets. Stock is a 70 so I bought a 67.5 and a 65 and also a 72.5 and 75 just in case. Like you've said and I've read, the velocity of a big bore pulls more fuel in through the stock carb and jet and makes it run too rich, so you're supposed to drop the main jet a bit. I should also open up the air screw a bit for that low throttle, bog issue, right? Karl PS Torqued the head at ~13 ft. lbs according to this......... motor.mortch.com/support/scooter/engine/1e40qmb.pdf |
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Post by rallyrrr on Aug 13, 2008 22:29:56 GMT -5
Check your end gaps with the rings square in the bore about where they would be with the piston at TDC. 0.10-0.12mm per inch of bore. File to specs and chamfer resulting sharp corners if necessary. Ex: 40mm/25.4mm per inch x 0.10mm
1.57 x 0.10 = 0.16mm : minimum
1.57 x 0.12 = 0.19mm : maximum (rounded off)
Easy. It doesn't take much filing to get you there.
I've never heard of oil control rings on two strokes.
Ring in groove clearance should be 0.04 - 0.10mm. Ratt tatt tatt tatt.
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Post by rallyrrr on Aug 13, 2008 22:34:55 GMT -5
Oops too late. Already assembled.
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Post by 90GTVert on Aug 13, 2008 23:10:21 GMT -5
What should you use to lube the piston bearing before installing the piston also shouldn't you coat the cylinder bore with 2 cycle oil before inserting the piston I use assembly lube. For some reason the parts stores here keep it behind the counter, so you may have to ask for it. Brent, just getting to you on this and I did respond to your email, thanks, man. That's what I figured, too. I guessed that the ring package could have been for any 50cc engine, either 2 or 4 stroke and that the oil control ring would be sandwiched between the two rings on one ring land, and there would have been another set for the other ring land. It's all put back together and started right up. I do need to jet it correctly but I'm waiting on those parts to come in. Should be here by the weekend. Glad I could help, and glad to hear it's running. I bought 4 jets. Stock is a 70 so I bought a 67.5 and a 65 and also a 72.5 and 75 just in case. Sounds like you will be well prepared to tune. I've got a little bog/hesitation at about 1/4 throttle. I had the jet needle clip at one setting below middle or 2nd from the bottom, but I put it back to stock. It still has the bog. I should also open up the air screw a bit for that low throttle, bog issue, right? If the bog/hesitation is starting around 1/4 throttle it could still be your jet needle setting. Moving the clip higher will lean the mixture more and moving it lower will richen the mixture more. I would suggest starting by setting your idle speed near where you want it, then adjust the mixture screw to achieve the highest RPM, then turn the mixture screw about a 1/4 turn in from there, then re-adjust your idle RPM. Honestly, I hate tuning these small carbs and still suck at it. It's a trial and error sort of thing in most cases. |
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Post by rallyrrr on Aug 14, 2008 0:01:05 GMT -5
When I get close I always check for throttle response and make the final adjustment for best response . Atmosphereic conditions will throw this off a little bit from day to day.
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Post by Karl on Aug 14, 2008 8:36:40 GMT -5
Thanks Gents! I'm off to work but will be back on here later today.
Karl
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Post by w8tlftr on Sept 22, 2008 15:06:36 GMT -5
I watched a cylinder install on a Honda dio I think it was and he had 3 rings two main rings and one which is designed to help thrust the oil onto the cylinder walls it went under the last ring if I am not mistaken, my scoot only had 2 rings and in the piston groves there are notches where the rings should sit when installed, I had to pinch the rings tight to the notch as I slid the piston into the lubed cylinder, I i assume your rings also may have a slant they should go in with the slant in a certain position, I do not remember which way sorry, mine were not slanted on my Malossi cylinder kit so it didn't matter, also remember when putting the surclips in to hold the piston in place make sure they both are turned in the same dirrection on both sides of the piston, mine were really jacked up cause I have seen much better surclips like in a G shape, mine were c shaped and not easy to install in the groves and getting them the same wasn't really possible, also don't forget to lube your piston bearing before you install the piston.
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Post by motomech on Sept 22, 2008 19:51:44 GMT -5
Check your end gaps with the rings square in the bore about where they would be with the piston at TDC. 0.10-0.12mm per inch of bore. File to specs and chamfer resulting sharp corners if necessary. Ex: 40mm/25.4mm per inch x 0.10mm 1.57 x 0.10 = 0.16mm : minimum 1.57 x 0.12 = 0.19mm : maximum (rounded off) Easy. It doesn't take much filing to get you there. I've never heard of oil control rings on two strokes. Ring in groove clearance should be 0.04 - 0.10mm. Ratt tatt tatt tatt. <<<<I've never heard of oil control rings on two strokes.>>> Me either. |
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Post by motomech on Sept 22, 2008 20:19:50 GMT -5
<<,Honestly, I hate tuning these small carbs and still suck at it. It's a trial and error sort of thing in most cases.>>>
Here's my method for jetting.
I alway focus on the main jet first. It can be tricky on a two-stroke, because often, a two-stroke will surge on top, irregardless of whether it's lean or rich. This is where a manual choke on a motorcycle is so useful. Applying half choke can tell you which way to go.
I would be careful of going down on the main jet size, until you are sure.
Next is the pilot jet, which is straightforward. If the engines starts and idles nicely, without turning the mixture screw out more than three turns, the pilot jet is ok.
Only after these two have been taken care of, would I mess with the needle position(if the need is there).
If the needle is not adjustable, I would recommend that one goes to a shop and beg or borrow some of the special shims that are left over from jet-kits. These are in 1/2 millimeter increments(one clip on an adjustable needle is one m/m).
Many years ago, I just couldn't get my built RD350 to run cleanly down low with open filters. Most folks just put up with it for the extra top-end, but I wanted it perfect. No combo of mains, pilots or needle positions would clear it up.
Eventually, a legendary two-stroke tuner turned me on to the fact that I had to change the needles and nozzles. The thin tapered needle was swapped for a "fatty" needles and the nozzles I installed had much larger perforations. Bingo, different bike.
I wasn't sure at the time why this change worked so well until one day, while studying carb theory(Kevin Cameron, tech editor of Cycle), described the manor in which the fuel exits the nozzle as it enters the air stream for mixing. He described the perfect state of the fuel as "stringy blobs". A two-stroke needs a certain of restriction in the induction track to achive this and when the restriction is reduced, the path for the fuel to move though the nozzle needs to be eased.
Yeah, that's what it's all about, perfect stringy blobs.
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Post by motomech on Sept 22, 2008 20:34:41 GMT -5
I watched a cylinder install on a Honda dio I think it was and he had 3 rings two main rings and one which is designed to help thrust the oil onto the cylinder walls it went under the last ring if I am not mistaken, my scoot only had 2 rings and in the piston groves there are notches where the rings should sit when installed, I had to pinch the rings tight to the notch as I slid the piston into the lubed cylinder, I i assume your rings also may have a slant they should go in with the slant in a certain position, I do not remember which way sorry, mine were not slanted on my Malossi cylinder kit so it didn't matter, also remember when putting the surclips in to hold the piston in place make sure they both are turned in the same dirrection on both sides of the piston, mine were really jacked up cause I have seen much better surclips like in a G shape, mine were c shaped and not easy to install in the groves and getting them the same wasn't really possible, also don't forget to lube your piston bearing before you install the piston. All good points. The beveled ring is called a Dyke's ring and is always on top with the bevel facing up. the idea is that the cyl. pressure gets in behind the ring and forces it outward. Cir-clips are best installed with a quality pair of sm. slender needle nose plyers. Once the clip is in, it should be rotated so the open end is not aligned with the notch in the grove. Always keep a finger on the clip when installing because these things really want to fly. That is also why rags are always stuffed in the crankcase hole. I lube the cyl. wall and sm. end brg. with the two-stroke oil I intend to use. |
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Post by w8tlftr on Sept 23, 2008 8:17:27 GMT -5
Where I got alot of my info was from a guy that post alot of very informative videos online , at the end of the video I will paste here he discribes the three piston rings, and what the last ring does,I learned alot just watching some of his videos, he has over 300 plus vids on anything you can think of, to me he's like a Moped guru haha, after watching I had no fear doing all my work on my scooter myself even though his scooters are not Piaggio, it's all the same really or very similar. Check out some of his videos, www.youtube.com/watch?v=ssvX-AH_pWY , when I respond to a question on here I try to answer in a simple format because reading from a text book or posting all the spec's makes a person think no way I can do this myself, so then they go and pay some mechanic 75.00 per hour or more, to do a job thats really not that hard at all, half my dirrections were in french, but after watching how it was done in a video I didn't need all that tec data.Anyway I hope some of you check out some of this guys videos it's pretty simple to understand and will make you yourself a pro mechanic in no time : ) |
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