|
|
Post by smooch on Feb 14, 2020 22:31:34 GMT -5
Big end failure. I have since replaced the CS and upgraded to the airsal piston. Which IIRC is lighter than the standard 50mm, also domed a big plus. |
|
|
|
Post by AtariGuy on Mar 2, 2020 13:32:29 GMT -5
Update - current 50mm bbk on my 139qmb is still running strong at 2000 miles clocked. This weekend is start of season inspection and lube service. New tires on the list but that's not related to this thread...
|
|
|
|
Post by smooch on Mar 4, 2020 23:29:17 GMT -5
Yes I have one in my taotao 50cc. 50mm piston big valve heads A9 cam. It has about 3000mi on it still going good. Time for a upgrade to a 150cc. I need speed.
|
|
|
|
Post by smooch on Mar 4, 2020 23:31:25 GMT -5
Yes I have one in my taotao 50cc. 50mm piston big valve heads A9 cam. It has about 3000mi on it still going good. Time for a upgrade to a 150cc. I need speed. Mine is a 1p39qmb.
|
|
|
|
Post by jjribs on Apr 3, 2020 22:40:24 GMT -5
For what it's worth. I've done the bbk's that are basically 81cc. I've used the original 50cc head on the 1st one, lost the big end of the con rod on a low mile case. Got ran over, 8 crushed ribs, hole in my lung, and, well I digress. Flipped to another scooter, same type bbk dogged it at 9.5 rpm for about 900 miles. Lost a right side bearing. Now I'm on my new crank and same cylinder. Never had to remove the piston from the cylinder to put it all back together. Don't know why anyone should. Anyway, I see a lot of logic on these posts about compression, piston weight, etc. I DO KNOW that compression has a LOT to do with the life of the engine on a bbk. That is the easy part. Next comes the crank bearings, with practical compression. The lower the better, I'm sure. That, AND keep it below the 8K Chinky bearings. On all of my engines I did moderate to major port matching, etc. Why not? You could do that with the most basic drill tools. I just consider volumetric efficiency for the desired rpm that I want. The oil pump issues I have yet to encounter. That will probably be tomorrow, or the next day, on this hinky chinky b/s...
|
|
|
|
Post by mikerides on Apr 9, 2020 10:12:00 GMT -5
I've just installed a 88cc big bore kit (52.4mm)I only have 115 miles on it haven't had any issues wirh it at all still breaking it in but does 45 easily and that's under 8k rpms it great to see other people's experience with I definitely learned a lot reading thru these comments I have a 150cc carb on it which made a big difference me head with a9 cam
|
|
Senior
Scoot Junior
At over 1000 miles on the 50mm kit
Posts: 7 
Location: Camden,De
|
Post by Senior on May 12, 2020 15:20:04 GMT -5
The wolf Rx 50 has over 2000 miles and is still pulling well. I did a gear change and it nocked the RMPs down.
|
|
Danny87
Scoot Junior
Posts: 7
Location: Connecticut
|
Post by Danny87 on May 12, 2020 21:07:05 GMT -5
May be a bit off subject...I saw a guy on youtube who installed some kind of crankshaft pressure relief hose with a "bullet tip" out of where the oil dipstick used to sit in. I think that it may be good for 100cc BBK because bbk builds up a lot of pressure on the bottom end that can cause some kind of piston rings/crankshaft seal failure that causes short engine life. I will try to look into where I got the info from...
|
|
Danny87
Scoot Junior
Posts: 7
Location: Connecticut
|
Post by Danny87 on May 12, 2020 21:27:45 GMT -5
www.youtube.com/watch?v=ekJQaOF43Iw2:50 in the video its called breather kit. I noticed that a lot of people who are running BBK don't have it. I had 04' crf450.One day, I was riding at a local track..the crankcase breather vent hose accidentally got pinched shut that I ended up with having to replace crankshaft seals over and over without realizing it in the first place! BBK does build up more pressure in the bottom end so I'd maybe look into that for scooters? IDK.
|
|
|
|
Post by GrumpyUnk on May 13, 2020 7:06:11 GMT -5
As the piston goes up and down in the bore, the volume of air (not including oil & engine pieces) the crankcase varies by the displacement of the piston. i.e., XXcc. Of course the air will either compress/decompress or blow out of the breather. If it does not, it will attempt to leak out past the seals and gaskets. It will likely push oil that happens to be in its way, such as on the bearings, out ahead of the air. Thusly the seals may leak. To prevent that, insuring that your breather works properly will alleviate the buildup of pressure. To a degree. Some small outdoor equipment engines use the pulses of pressure in the crankcase to operate a fuel pump. The pressure pushes against a diaphragm which in turn pressurizes the inside of a fuel pump to push fuel to the carburetor. A return spring moves the diaphragm back, and fuel is pulled from the tank via check valves.
So, make sure your vent is working or you will have leakage. The pressure developed will be directly related to the vent and the displacement of the piston when it cycles.
tom
|
|
Petro
Scoot Enthusiast
Posts: 149
Location: Gothenburg, Sweden.
|
Post by Petro on Jun 16, 2020 13:46:19 GMT -5
www.youtube.com/watch?v=ekJQaOF43Iw2:50 in the video its called breather kit. I noticed that a lot of people who are running BBK don't have it. I had 04' crf450.One day, I was riding at a local track..the crankcase breather vent hose accidentally got pinched shut that I ended up with having to replace crankshaft seals over and over without realizing it in the first place! BBK does build up more pressure in the bottom end so I'd maybe look into that for scooters? IDK. Saw this years ago and did my own test. Took a large clear hose and clamped it directly on the case filling hole after removing the oil filler plug. Starting the engine it spit and sucks but after say 10 seconds the oil filled the hose like 2-3 inches and stays level there. When I gave it throttle it sunk a bit and came back to level... some bubble sometime but nothing alarming... I didn't see anything strange with that so I didn't bother, thinking that the stock ventilation is enough (4mm if I remember correctly). All the testing made on the double stand, not driving but I never had any problems with anything related to presurized crankcases. |
|
|
|
Post by CrankingWithCG on Nov 25, 2020 18:52:24 GMT -5
So just as a question, will the stock crank take the abuse from a 52mm bore? And do you have to cut the cases??
|
|
Petro
Scoot Enthusiast
Posts: 149
Location: Gothenburg, Sweden.
|
Post by Petro on May 15, 2021 4:29:42 GMT -5
I just past 15.000 km, around 9000 miles and still going strong.
|
|
|
|
Post by scooter7878 on Jun 2, 2021 5:21:39 GMT -5
Over 3000 miles still going I beat the balls off it at times I hit 9500 rpm I'm pretty much full throttle 90 percent of the time I'm pretty much trying to blow it so I can get a naraku 52mm cylinder and head with a stroker
|
|
|
|
Post by steve1297 on Jul 19, 2021 7:03:00 GMT -5
I have a 52mm. It stretched out the timing chain after about 3000 miles. The tensioner may have been bad. But I replaced it. Also the vibrations strip out the exhaust studs.
|
|
