What's the maximum RPM you"ve reached?

itchybird said:
In my mind, a two stroke tach should be different than a four stroke tach, right? At least in calibration.

Case in point:
A two stroke fires everytime the motor is at top dead, but the four stroke fires every other time. So a tach calibrated for a four stoke accounts for that fact, ie four stroke RPM is the number of spark firings times two.

If you then throw that tach on a two stroke, it would indicate twice the RPM. ie two times for each fire. Hence it would read TWICE the RPM as the same tach on a four stroke.

Ain't that right guys?

Rich
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Actually the 4 stroke fires the same as a 2 stroke.
Only 1 of the sparks is in the exhaust.
So any tach is fine.
 
I have an electronic tach/hour meter on my engine that goes up to 9,999 rpm's before it goes back to zero. I've seen it as high as 300, which means 10,300 rpm's. At that engine speed, the bike is going 41mph, which is as fast as I've had it up to, and as fast as it will go with the current gearing....

Warner
 
Riding Rich said:
Actually the 4 stroke fires the same as a 2 stroke.
Only 1 of the sparks is in the exhaust.
So any tach is fine.
Click to expand...

Rich,
Most four strokes do not fire on the exhaust stroke, but only on the compression stroke. It all depends on the make model and year of motorcycle. All of the British bikes and older Harleys fire
only on the compression or power (3rd) stroke.
 
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Riding Rich said:
Cool

I'm going to order a Tach right now so i can see how far i push the rpm's.
Click to expand...

It's very cool...and I think it was about $35 from Staton. The other useful thing is that it doubles as an hour-meter so you can see how many running hours your engine has on it....for maintenance, etc....

Warner
 
Riding Rich said:
Thunder Products - Performance carburetor and clutching for snowmobiles, motorcycles and ATVs.

Thats what i'm getting.

9000 rpm might not be high enough.

But that i will find out.
Click to expand...

Rich,
Take a look at the "Tiny Tach" it will go to 10,000 rpm and is very reliable and accurate to
10 rpm's also. Google part number TT226NR and choose who to buy from. They sell for
about $33.00. Its the one that I use and it's small in size too. It records the total amount
of running hours on your engine which shows on the meter when not running. Mine displays
42 hours. Perfect for maintenance issues!
 

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The digital tach that I have also doubles as an hour meter. When the engine is off, the meter will show how many hours it has on it. When the engine is running, it shows RPM's. After 9,999 RPM's, the meter reads 0.....but then after that it starts over at 1. So for instance instead of reading 10,400 RPM's, it will simply read 400. So it really does read higher than 10k RPM's....

Warner

Here's a link to the one that I have - It's $36 including the bracket:
Motorized Bicycles Detail Page
 
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I've got a TinyTach on my bike and I think the highest I've seen is about 6600 which is up from a week ago. As of Tuesday night I've got 120 miles on the engine and maybe 7 hrs total. At that RPM the engine is whistling big time, from what I've read here that's because of the straight cut gears. I suspect as it breaks in more the rev's will get higher. I've also seen a top speed of 28 on the flats and hit 30.8 on a down hill. I've ridden it pegged mostly since day one so we'll see how it breaks in , in what another couple hundred miles or so?
 
Ehhh, it might get a little smoother, but it shouldn't change much after 120. Im my experience the break ins are mostly finished after 50 miles. You can defninitely go past 7000 if you jet that thing right, but 28 is definitely a respectable number for stock, and im sure it has torque up the wazoo.
 
Phil,

I agree with you, I think it's about tapped out for RPM, can't really see it going much above 7K if I even make it to that. It has gone up about 1K since I initially started riding and top speed has gone up about 3-4 mph but I'm certainly impressed with the little 66cc motor doing as well as it has. If I can hit 7-7500 rpm, 30 mph and 100+ mpg I'll be pretty jazzed. After 3-500 miles I'm thinking I'll get a jack shaft kit and see if I can get the speed up to 35-40 and boost the mpg figures. That's the goal anyway.
 
I would be interested to find out what my engine revs to. It used to vibrate rather badly until I had a couple friends help me remount it. It turns out that the engine was leaning to one side severely and it seemed that the chain was twisting quite a bit as it ran. I righted the engine and since doing that vibrations have decreased substantially. I messed with the throttle a bit too and it now revs much better too. I wouldn't be surprised if I can get it to 7000+.
 
Hey boys if it makes you feel any better after 300 miles of HARD riding, his engine is retired. It lost a lot of power and wouldn't turn over. After tightening the clutch and turning over the engine the piston started slapping the head. After adding a head gasket it is clear that the bearings are shot. it still runs but its got no power. I told him id fix it, but it'd cost him more than a new engine. In the meantime i told him to run it 16:1 with a real rich jet and hopefully it will last him the rest of the school year.

Moral of the story: Its probably not good for your engine to run consistently past 9000 RPM.
 
My question is after checking the manual and finding that 6000 rpm is the rated redline on my pk 80, what is a SAFE rpm to run without taking out the lower rod bearings?? Keep in mind that I trued up my crank and run a stihl bearing on the top end. I burst to 6500 rpm occasionally but need a definite SAFE rpm to go by.........
 
Prasinos said:
Hey boys if it makes you feel any better after 300 miles of HARD riding, his engine is retired. It lost a lot of power and wouldn't turn over. After tightening the clutch and turning over the engine the piston started slapping the head. After adding a head gasket it is clear that the bearings are shot. it still runs but its got no power. I told him id fix it, but it'd cost him more than a new engine. In the meantime i told him to run it 16:1 with a real rich jet and hopefully it will last him the rest of the school year.

Moral of the story: Its probably not good for your engine to run consistently past 9000 RPM.
Click to expand...

If you are using a chinese frame-mounted 2 stroke, I would agree with that. Lots of the Japanese (usually in a rack mount configuration) engines are perfectly fine running at those higher revs for extended periods of time.

Warner
 
mountain80 said:
My question is after checking the manual and finding that 6000 rpm is the rated redline on my pk 80, what is a SAFE rpm to run without taking out the lower rod bearings?? Keep in mind that I trued up my crank and run a stihl bearing on the top end. I burst to 6500 rpm occasionally but need a definite SAFE rpm to go by.........
Click to expand...


It would depend on what the limiting factor was on the original redline. If it was any of the things you changed or corrected, you'd probably be safe going higher. Without knowing what was the limiting factor on the original recommended redline, it's impossible to say if what you updgraded would move the safe redline higher or not.

Warner
 
Engine redline is based on piston velocity...fpm (feet per minute).

Small bore, long stroke...lower redline when compared to big bore, short stroke.

Jim
 
Creative Engineering said:
Engine redline is based on piston velocity...fpm (feet per minute).

Small bore, long stroke...lower redline when compared to big bore, short stroke.

Jim
Click to expand...

Sure.....but components around that piston are usually what fails, so beefing up certain components (connecting rods, rod bolts, valve springs in a 4 stroke, etc) can increase the safe rpm level for an engine, which was my point. The weakest link will fail first.

Warner
 
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