HT engine True MAX RPM

[210061741]

Ok they say that these run only 4500 rpm.
I have a GT-2B 48cc and gotta be running alot higher than that.
I know i cruise between 30 to 35 MPH with the SBP Expansion CH and no head gasket + DIY Boost Bottle and 36T rear sprocket.

With the 36T and calculated with a 26" dia nominal tire.
Which we know is less.

I would have to have an engine rpm of about 5800 rpm to hit 30 MPH.
I am confident i coul push 40 MPH out of her before i run out of Fuel / Air to sustain higher RPM.

At 40 MPH My motor would be spinnin 7632.83 RPM
I know i've been there.

A dealer told me 8000 max rpm.

Anyone have a tack that can tell us the truth.

 

[DougC]

If you have a DVM that does freq. counting, you could make a inductive (coil) sensor out of a bit of wire, and hold that near the spark wire with the engine running.
~

 

[Fabian]

Hi Rich

If you have been to 7000 rpm, you won't have a bottom end bearing for much longer.

I revved my 1st engine to 5600 and it would not rev any higher - 35 miles later the engine blew the bottom end bearing.

With my second engine, i accidently revved it to 4800 and around 60 miles later, it's making bottom end bearing rattling sounds.

7000 rpm, it posssible, anything is possible, but you'll have stuffed the bottom end bearing.
Expect the big end to c.r.a.p itself fairly soon.

You're best off disassembling the engine before the bearing fails and metalic particles damage the piston/rings and chrome plating on the cylinder bore.

Fabian

 

[iron_monkey]

These engines are not designed for high rpm.

Although my engine has probably seen 6000rpm due to someone wanting to WOT it for 1 second in neutral a couple of times.

That was 100km ago, hope it doesnt fail.

 

[Skyliner70cc]

I rev the carp out of my HT engines with no problem ever with lower end bearing. I've had one issue with wrist pin bearing from overrevving but that was 2 years ago.

Some folks have successfully used a Stihl wrist pin bearing whch is rated for much higher revs.

I'm sorry to hear about your engine failure Fabian. I'm sure you know that an engine should never be revved high without a load.

 

[wildemere]

I've got an old bushing 70cc motor that sees 6000+ rpm every ride.

Its 2 years old and sees about 100km or 60 miles per week.

I've only done one big end in all that time, that was the result of a lean out and overheat.

Its still on the original barrel though.

 

[Fabian]

I find it amazing at the number of people who have had no mechanical problems with their 2-stroke engine kits.

The distributor/retailer from who i bought my engine kit has admitted a big end bearing failure rate of 4 in 10 engines, the others failing due to incorrect oil/fuel ratios.

I am working with the distributor preparing an extensive PDF to be sent to the engineers of the Chinese manufacturer, photo documenting all the failures and suggesting rectification methods to fix their shocking reliability issues.

Fabian

 

[210061741]

Well like i said i don't really know for sure.
And i do think my engine is getting tired.
However it still runs great.
I ride hard and like Fabian I play the terrain.
Only difference is i don't have gears.

 

[Skyliner70cc]

Fabian,
Very noble, but do you thing that the same folks who poison (adulerate) pet and people food so lab tests show higher than actual protein levels actually care about making things better? If you get them to improve their product, I'll buy you a beer!

 

[arceeguy]

....but do you thing that the same folks who poison (adulerate) pet and people food so lab tests show higher than actual protein levels actually care about making things better? If you get them to improve their product, I'll buy you a beer!

I was unaware that the same factory that made bicycle engines made pet and people food!