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Post by duosport on Feb 9, 2010 19:58:15 GMT -5
jmstar,
I checked out the site. Interesting. I see lots of pistons listed and it is a series of oversized pistons for larger and larger bores. The first two pistons listed are STD size 40mm bores. The interesting thing is when you go to the application or what scooters it fits, it lists many scooters that have the Minarelli engine. The JOG 50 and the F15 are both listed. This suggests that the cylinders are completely common between them.
Thanks for that.
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Post by Fox on Feb 9, 2010 20:33:24 GMT -5
jmstar, I checked out the site. Interesting. I see lots of pistons listed and it is a series of oversized pistons for larger and larger bores. The first two pistons listed are STD size 40mm bores. The interesting thing is when you go to the application or what scooters it fits, it lists many scooters that have the Minarelli engine. The JOG 50 and the F15 are both listed. This suggests that the cylinders are completely common between them. Thanks for that. No sweat! bro! I hope you get that thing running soon and you better post some pics or a video even or I/we will all be disappointed.  If you need help posting pics ask and you shall receive. |
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Post by duosport on May 2, 2010 18:34:13 GMT -5
OK so I realize it is a couple of months later but I did order the piston and rings and I did get them and the rings sent with the piston were not the correct ones so I had a bit of recon work to get the right ones and I eventually did. I installed the piston and rings. I checked the gap it was OK and I oiled everything. I used new gaskets all around. I torqued the bolts and I partially reassembled the scoot. I cranked it by hand a few times and then fired it up and it started straight away. When I got to the point of taking it for a ride I noticed the scoot lacked umpf just like before. 22 mph tops. So I did a compression test and got a reading just as before the new rings and piston. 90 PSI.
One thing I did not do is check the head for flatness. The condition of the cylinder and head were visably excellent. So 90 PSI. I am wondering if my gauge is bad because the scoot fires up so quick and easy and it sounds nice on the stand.
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Post by 90GTVert on May 2, 2010 19:15:05 GMT -5
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Post by duosport on May 2, 2010 20:08:34 GMT -5
That would test the whole engine basically. Crankcase and all. But I pretty much need to solve the top end lack of compression first though right?
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Post by Fox on May 2, 2010 22:24:07 GMT -5
It may not be the engine at all. Have you inspected/cleaned the CVT components?
If the roller weights are jammed up in the CVT then you'll have issues with performnce.
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Post by duosport on May 3, 2010 6:34:19 GMT -5
I have done nothing with the CVT at all. I have cleaned the carb several times and I performed a compression test which gave me the low reading. So I took that to mean rebuild the top end. I opened up the cylinder and the top ring was visibly worn small so I figured that was the problem. You may very well be right about something other than the engine but what about the low compression? If it is not the engine then either the guage is bad or the manner in whch I used it was bad.
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Post by Fox on May 3, 2010 6:48:55 GMT -5
Well duo, even in my sleep-deprived, insommniatic state I think that if you haven't gone through the entire engine and drive system then you are clueless as to the condition of your engine. Look, I mean no disrespect but it's obvious you are a rookie mechanic so you should take this advice: If it looks like a duck then it's a duck. If it's a swan and acts like a duck then something's wrong. You need to learn all you can about how the entire engine works so you aren't asking the wrong questions. Have you seen this vid? It's a 4 stroke but it's the same thing. www.youtube.com/watch?v=viWOOvy45wI |
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Post by stepthrutuner on May 3, 2010 10:47:41 GMT -5
I have done nothing with the CVT at all. I have cleaned the carb several times and I performed a compression test which gave me the low reading. So I took that to mean rebuild the top end. I opened up the cylinder and the top ring was visibly worn small so I figured that was the problem. You may very well be right about something other than the engine but what about the low compression? If it is not the engine then either the guage is bad or the manner in whch I used it was bad. |
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Post by duosport on May 3, 2010 19:03:57 GMT -5
..Look, I mean no disrespect but it's obvious you are a rookie mechanic ... I would be the first to admit that. |
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Post by duosport on May 3, 2010 19:06:35 GMT -5
I have done nothing with the CVT at all. I have cleaned the carb several times and I performed a compression test which gave me the low reading. So I took that to mean rebuild the top end. I opened up the cylinder and the top ring was visibly worn small so I figured that was the problem. You may very well be right about something other than the engine but what about the low compression? If it is not the engine then either the guage is bad or the manner in whch I used it was bad. I took your advice and tried the guage on my old push lawn mower and registered a 115 PSI. I guess this tells me it is possible to register a different number than simply 92 PSI. Maybe my mower is really pushing 125 PSI. I also checked for leaks with a spray of soap water and saw none. |
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Post by stepthrutuner on May 3, 2010 19:35:46 GMT -5
Well at least now you know you can trust your comp. gage. and look for something else. Piston-in-bore clearance?
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Post by duosport on May 3, 2010 20:24:02 GMT -5
Meaning the clearance of the top of the piston at its apex to the cylinder head? Or do you mean something else?
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Post by stepthrutuner on May 3, 2010 21:58:21 GMT -5
Meaning the clearance of the top of the piston at its apex to the cylinder head? Or do you mean something else?
www.indianmcinfo.com/Indian_stuff/pdfs/Lesson/2stroketopendinspectionnbr12.pdf
Unfortunately you need special measuring tools to do it properly (especially a cylinder dial bore gage). So to get a really good piston-to-bore fit it would be easiest and probably just about as cheap to just get a new cylinder and piston (preferably a big bore). I think your scooter has some other problem other than low compression that is causing it to run poorly. |
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Post by duosport on May 4, 2010 19:34:10 GMT -5
I do not know if this really amounts to anything but I thought I would ride the scooter hard up some hills and then go fast down hill andcoast the engine to some stops. I read this was potentially good for seating the rings. I rode it around for about 30 minutes or so this way. It went about 3 miles faster on the flats than it did two days ago. I let the engine cool down and then I did a compression test on it. It was actually slightly higher up from 90 PSI tyo 92 PSI. Obviously this is way low but it is going up.
I read the above primer on piston rebuilds and one thing I did not do is scuff the inside of the cylinder. I read this helps seat the rings. Maybe my lack of doing this is making it hard for the rings to seat.
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