Gorr's 144's

[2-Strokes 4-ever]

Hearing only positives about his boring and porting work, I purchased a thrashed 125 cyl off flea-Bay. Our 125's due for a lower-end look at anyway and when January and February's cold hits the plan was to order a 144 bore job along with low-end (woods) porting.

Then there's the nay-sayers...... "John, it'll eat up pistons like mad. Bigger bore, larger ports, less piston contact area..."
This 125 has always been long lasting on top ends. With proper jetting, a clean air filter, and low-ish RPM woods riding, we can go 40 hours before ringing it and another 30-40 hrs before a new piston.

Can someone give me an estimate of true top end longevity in comparison to after Gorr's work?

Thanks, John

 

[2strokerfun]

I don't buy that argument. A 250 lasts much longer than a 125 and it has bigger ports. But it also has LOTS more surface area on the piston because of the bigger bore (of course the rpms play a huge part of a 250 lasting longer). A stock 98 RM125 has 54mm piston, which would give circumference of approx 169.65mm. If the 144 piston is 58mm, it would have a circumference of roughly 182.21mm. That would mean the ports would have to be at least a total of 12mm larger for you to have less ring or piston contact area. And any given point on piston or rings is only exposed to the ports for a portion of the stroke.
Couple that with the increase in power from the 144, which would often mean you aren't ringing the engine out to the nth degree every second you are racing/riding, and my thoughts are that the 144 top end would last a bit longer, all else being equal.
Someone who has done this will chime in and tell you if I'm right or full of it (some days, it's a coin flip).

 

[2-Strokes 4-ever]

I don't buy that argument. A 250 lasts much longer than a 125 and it has bigger ports.

Thanks for the input, and this is why I ask the question.

Although my RM250 is ridden at fairly low RPMs (compared to a 125), it wears out top ends at about the same rate as our 125 does. The 250 has the stock bore, but has been extensively worked-over by Varner Motorsports (porting, cyl decking, and head work.)

 

[whenfoxforks-ruled]

The 5~7 hour top end life in stock form, that stays the same. Someone has some issues with maintenance? So blame it on Eric? Vintage Bob

 

[2-Strokes 4-ever]

Huh? Nothing's blamed on Eric.

Simply a "big bore" longevity question.

 

[whenfoxforks-ruled]

Huh? Nothing's blamed on Eric.

Simply a "big bore" longevity question.

I was NOT implying you, the people telling you this bs though! If it compromises the job, he will tell you!

 

[2-Strokes 4-ever]

I was NOT implying you, the people telling you this bs though! If it compromises the job, he will tell you!

Thanks.
My riding "buddy" is pure pro at bringing out a negative point.

I believe Mr Gorr knows what he's doing and didn't want to use his time with a phn call at this point... just do a little pokeing around here first.

 

[oldguy]

Eric did my 03 RM125 2 years ago as a 144 with porting to keep a fat old man safe and it has about 30 hours on it with no loss in compression yet. It has been ridden by a friends daughter for about 15 hours when she was jumping up from an 85 to a 125 so the set up was ideal to give her a safe transition. It has also been ridden extensively by several of my sons friends that rung every ounce of power they could on MX tracks. This winter it is going to see duty on the ice

 

[Senior KX Rider]

Changed the rings on my KX144 at about 25 hours just to get a look at things. Could have gotten much more out of them :nod:

 

[whenfoxforks-ruled]

What did the skirt clearance and ring gap measure? 25 hours is pretty long, compared to the book. How long did Eric recommend?