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View Full Version : How to install a bigger crankshaft


James2132
04-05-2014, 05:59 PM
Hi I have a taotao 150cc scooter and im trying to install a bigger crankshaft for more power but there's hardly any info on how to install these bigger high proformance crankshafts. What's the biggest u think I should go? I saw one in ebay that was +8.2mm! With the 63mm cylinder I'm gonna install I estimate I will have about 232cc or more. I notice all of the crankshafts have a thing call a woodruff key space how do i install these?? Thanks.

blueboy5000
04-06-2014, 08:44 AM
Well if you're not familar with what a 'woodruff key' is, you should probably not use your 150cc engine as a learning process! (it's a little rectangle of hardened steel that sits in a groove on a crankshaft)

A 63mm cylinder requires BORING of the cylinder, which requires HONING of the cylinder as well (unless you purchase the "jug" pre-bored and honed) milling of the jug may be required to fit properly, as well as a MINIMUM of 2 base-gaskets.

This is NOT a first-time try and see experience, crank and BBK is the most difficult mods possible to a gy6. Removing the old crank bearings requires use of a torch. Reinstalling the crank bearings requires FULL diss-assembly of the ENGINE CASE and full cleaning, as you will have to heat the block in an OVEN and freeze the new bearings in a FREEZER or DRY ICE bucket to make them fit. I have found no way to accomplish this without use of heat and cold.

Again I state this is a VERY DIFFICULT mod, not for the inexperienced.

Your 232 engine will require a much-modified carb, bigger cam(s) and would greatly benefit from improved CVT and OIL COOLER as well. A 232cc runs much hotter than the stock gy6 157.

James2132
04-06-2014, 04:23 PM
Thanks. Yes rebuilding gy6 engines can be difficult but it's something every scooter owner will have to do eventually anyway, replacing top end crankshaft etc.... Unless they pay someone else to do it, which is too expensive for me. So I might as well learn now. I have about 2800 miles so far. From what I have heard that's about half the life of a gy6 engine. 6000-7000 miles. I ride wot a lot, really don't have much choice because it's hard keeping up with traffic where I am.

blueboy5000
04-07-2014, 07:58 AM
I never ride mine at WOT as it would be going 65 to75 mph and that is unnecessary as I am not allowed on limited access highways.

A gy6 150cc should easily do 50mph at 6500rpm. Riding at WOT is extreme;y bad for ANY engine, not just scooters, NOTHING is designed to run at WOT.

And no, it is not true that 'every scooter owner' will need to replace/rebuild their engine at 6000 to 7000 miles, I've broke 10k miles on three gy6 bikes, and had no inner engine problems at all.

The key to engine longevity is proper maintainence and not abusing it. A 232 is FAR more sensitive and fragile than a stock 157, and will be even more susceptible to inner engine damage if ridden at WOT. It also isn't that much more powerful than your stock engine, only about 6hp, it will not make your bike have a higher top-speed as that is determined by the FINAL DRIVE gears, which limit these bikes to around 75mph maximum.

My current bike has no internal engine mods and easily hits 60+ mph.

blueboy5000
04-07-2014, 08:02 AM
Also, it costs 546 dollars to do a proper huge BBK (you're gonna need a new CVT with appropriate clutch and belt, a 30mm carb a bigger intake, cam and head, and engine gasket set) and you can purchase an entire new 200cc engine for 499. I'd just buy a new engine.

gitsum
04-07-2014, 10:47 AM
A gy6 150cc should easily do 50mph at 6500rpm. Riding at WOT is extreme;y bad for ANY engine, not just scooters, NOTHING is designed to run at WOT.

It's not WOT that is bad for any engine. It is the combination of high rpm's and excess heat that will significantly reduce the life of an engine.

That being said, WOT on most GY6 engines usually runs the rpm's at or near redline and the air cooled engine starts running pretty hot. I have a Taiwanese GY6 scooter that's tuned to run around 6800 rpm's at 55-60 mph and the engine temps usually run 320-340 degrees (CHT gauge). My philosophy is under 350 f and sustained rpm's under 7000 rpm's, no need to worry about speed or actual throttle position.

The wife and I have been touring two up riding like this for up to 300 miles a day. Close to 5000 miles and counting. I expect to get at least 25k out of the engine. When running the scooter hard like this I make sure to change the oil every 500 miles and check the valve lash every 1500 miles (only one adjustment needed so far).

I had a Yamaha C3 that was fuel injected and water-cooled, it ran WOT for nearly it's entire life. Last I heard it's still running strong.

blueboy5000
04-08-2014, 07:39 AM
It's not WOT that is bad for any engine. It is the combination of high rpm's and excess heat that will significantly reduce the life of an engine.

That being said, WOT on most GY6 engines usually runs the rpm's at or near redline and the air cooled engine starts running pretty hot. I have a Taiwanese GY6 scooter that's tuned to run around 6800 rpm's at 55-60 mph and the engine temps usually run 320-340 degrees (CHT gauge). My philosophy is under 350 f and sustained rpm's under 7000 rpm's, no need to worry about speed or actual throttle position.

The wife and I have been touring two up riding like this for up to 300 miles a day. Close to 5000 miles and counting. I expect to get at least 25k out of the engine. When running the scooter hard like this I make sure to change the oil every 500 miles and check the valve lash every 1500 miles (only one adjustment needed so far).

I had a Yamaha C3 that was fuel injected and water-cooled, it ran WOT for nearly it's entire life. Last I heard it's still running strong.

I cannot agree that it is a good idea to run at WOT or close to it, especially uphills or in hot conditions. My bike also hits 60 around 6500 rpms, but at WOT is is pushing 10,000 rpms, I would NEVER ride at approaching 10,000 rpms.

gitsum
04-16-2014, 03:13 PM
I cannot agree that it is a good idea to run at WOT or close to it, especially uphills or in hot conditions. My bike also hits 60 around 6500 rpms, but at WOT is is pushing 10,000 rpms, I would NEVER ride at approaching 10,000 rpms.

Is that 10,000 rpm's during acceleration or top end? If the engine runs that fast during WOT acceleration, then your variator weights are too light. If it hits 10,000 rpm's at top end then your gearing is too low.

Optimum gearing is reaching the maximum horsepower peak at top end speed on level ground.

You can change this with higher gears in the transmission, heavier variator weights, a larger diameter rear tire, shortening the variator boss, or any combination thereof. Just like tuning a carb there are multiple parameters and it can take some trial and error to get it right.

WOT itself is not always a bad thing, it is the combination of excess heat and too high rpms that you want to avoid. Some motorcycles/scooters are tuned/geared so that wide open throttle causes both, some are not. The GY6 engine is susceptible to higher engine temps when running a little lean, kinda of like a two-stroke, but not as much.

Proper carb tuning and optimum gearing can allow a GY6 scooter to perform at a higher level without compromising engine longevity/reliability.