red line on grubee?

6000 is a good safe redline, from my experience. Revving much over that on a bone stock engine tends to beat things up.
With a 26" wheel and 44T sprocket, 6K RPM is 26MPH. Some engines are balanced better than others from the factory.

A decently-balanced engine with some work can run ~7500RPM or more. How long it will last is basically a lottery question.
 
I have read that it is 7200. Take that with a grain of salt, i could well be much less on an unbalanced one.
 
I found out how fast it shouldnt go
picture.php
now Im still trying to find the right piston to replace it!
 
between 6600-6700 im going 30(speedo app on my phone) i havent checked at anything higher due to safety, i dont wanna be one handed going that fast, but if i had to guess, over 40 mph, if not its right at 40, but its screaming at that rpm, i run a rich mixture, wich i dont want to say due to the arguments of proper fuel mixture, but at those rpms for that amount of time the bearings and rings need all the lubrication they can get
 
waistofhumanspace said:
I found out how fast it shouldnt go
picture.php
now Im still trying to find the right piston to replace it!
Click to expand...

The piston pin hole actually could have moved from exessive heat. I had that happen to the gear driving the transmission of my nitro rc car. (except that gear was a plastic one.) If the piston pin still fits, then it will probably be fine. Worst case scenario: You have to change the port timing, but also get a higher compression ratio. Just make sure the piston won't hit the spark plug, or cylinder head.
 
there once was an older gentleman that made pistons.he had blanks that he machined to match failed ones.
a basement full of pistons and rings.

i read somewhere 7000 was redline on my 48cc grubee.
max reached so far is 6300,making my personal land speed record at 44 kilometres / hour.
vibrations are too much to keep it up for too long.
 
Last edited:
Das Chicken said:
The piston pin hole actually could have moved from exessive heat. I had that happen to the gear driving the transmission of my nitro rc car. (except that gear was a plastic one.) If the piston pin still fits, then it will probably be fine. Worst case scenario: You have to change the port timing, but also get a higher compression ratio. Just make sure the piston won't hit the spark plug, or cylinder head.
Click to expand...

That isn't going to work. You would need the rod for the new piston. If you try to do what is suggested the piston will hit the head and go no further. There's not a small difference there, it's a very large difference.

When I had my 151 GM/Jeep block rebuilt the machinest and I both thought the rods were 6.00 inches long. Somehow when the rods were polished and reconditioned by Competetion Products they ended up at 6.050 long so the piston stuck up out of the block. I had to get a thing called a block saver gasket. It goes on along with the stock gasket. I'd never heard of such a thing before but it saved me from having to get a new block. I haven't fired the engine yet and still wonder if it will hold up to the 12.5 to 1 compression ratio of the motor.
 
Last edited:
Someone on the forum said that there are over 25 ht engine factories in China. I have a generic engine with nothing what so ever on it, so if I needparts I'll have to use the ebay seller that the engine came from.
 
Das Chicken said:
The piston pin hole actually could have moved from exessive heat. I had that happen to the gear driving the transmission of my nitro rc car. (except that gear was a plastic one.) If the piston pin still fits, then it will probably be fine. Worst case scenario: You have to change the port timing, but also get a higher compression ratio. Just make sure the piston won't hit the spark plug, or cylinder head.
Click to expand...

Definitely not and definitely not and complete non-sense. They're just two different pistons, they're not interchangeable and that's all there is to that. Try again.
 
Cavi Mike said:
Definitely not and definitely not and complete non-sense. They're just two different pistons, they're not interchangeable and that's all there is to that. Try again.
Click to expand...

True, True, True, Im not new to the piston destroying game, I have scorched my Buell pistons on the "break in" there is no possible way the wrist pin could have moved evenly that much from heat. Apples & pineapples might both have apple in the names,
it dont mean they are the same thing
animated-gif.gif
Pineapple.gif
 
I have a PK80 68.5cc, CNS carb, 44t. I had my on the micometer once. And it did over 10000rpm. But also I still have to tune my carb better.
 
You must log in or register to reply here.
Back
Top