T500 something

[jimmer]

farmer92:aren't those engines crazy azz heavy?!! I think the crank alone is about 40lbs!

 

[farmer92]

farmer92:aren't those engines crazy azz heavy?!! I think the crank alone is about 40lbs!

That it is, i thought it would at least be somewhat like the rotax 503 i rebuild for my sled, but this thing is nuts.
Although it's not the heaviest, it sure as hell is for a puny little parallel twin.

Continued to tear into the "new" engine, looks like injection oil drained into the crankcase, or maybe it was filled on purpose, but there was an unpleasant oily surprise when i flipped it on edge. Got the case bolts removed, just need to get the cases to separate. So far i have been very pleasantly surprised with how nice the inside of this thing is, and how easily the bolts come out.

Hmmm which one shall i use?

 

[farmer92]

Finally have the cases apart and i am loving the insides of this beast

Although i would have gotten to this point sooner if the damn manual had mentioned this existence of this grime covered plate

 

[farmer92]

Not much of an update, cases are completely stripped, going to pressure wash the last 30 years of gunk off of them.
I wanted to try my hand at porting with this engine, since i have 2 sets of cylinders and the fellow who sold me the parts bike had 2 gt500 engines among other things, i am willing to try and possibly fail this at least once.

So the plans for porting are to raise the exhaust ports by 2mm and widen them by 3mm on each side into an ovalish shape
Similarily i will widen the intake by 3-4 mm on each side. Not sure if i should lower it by 1-2 mm as well.
The transfers will probably not change other than matching them and the gasket to the crank case.
Should be fun

Edit: hmm guess 3500 psi and a 15 minute bath in industrial degreaser isn't enough to get through the first 5 of the 30 years of grime... That shit is like welded on there mang

 

[jimmer]

Post '74 cylinders have less intake duration, the bottom of the intake is 5mm higher than earlier cylinders. So the torque curve is lower and less hp up high.

 

[farmer92]

Hmmm, i better cross reference the two cylinder sets then to be certain.
There's not really a whole lot of room to maneuver but we shall see what comes of it.

 

[jimmer]

Just incase there are T500/GT500 owners that don't know of this good general info : http://www.ozebook.com/compendium/t500_files/tech.htm

 

[farmer92]

Nice site, i found that one, as well as some posts on sundial to be quite interesting reads.
Finally mostly finished tidying up the ports, decided to go with the less is more mentality.

Didn't do much to the intakes, ground 1mm off each side, and angled the lower edge downwards to reduce the turbulence as the air "drops off" the edge of the intake.
Matched the ports to the carb boots.
Raised the exhaust by 2.5mm and widened it by 3mm
I may widen it some more, not sure though yet.
If anyone has any input/experience here it would be much appreciated.
I do not want to loose so much low end torque that i can't stand driving it, or have i done that by raising and lowering the ports already?

 

[jimmer]

Which cylinders do you have, early or late? Are you using stock carbs? What exhaust will you use?

 

[farmer92]

Have a set of 72' as spares
The ones i ground were from a 74'
I plan on buying some vm30's or 32's but i'll mull that over a bit
I was going to either build my own expansions or have a shop near by do it.
That way i can match the exhaust profile to the porting.

 

[jimmer]

I'd be inclined to go with 34's and lower the intake. The rest looks good to me.

 

[farmer92]

Any particular reason for the 34's?
I seem to remember reading that the first year had 34's and it guzzled fuel like a detuned Buick riviera towing a camper trailer.
Stock had 32's so i was planning on going with the same size. Smaller carb body means more velocity and more vacuum, which should make jetting easier to figure out.

 

[jimmer]

Porting and chambers is why. If a stocker can run 34's........ Either will work good. Round slide or flatslide?

 

[farmer92]

Was thinking round slides,
Will probably depend on what the costs of each are and on the availability/cost of jets as well.
If the costs are comparable, will probably get a flat slide, otherwise it will be the rounds.

 

[CarbsAndCylinders]

Talk to Teazer about porting, he did the porting for my Titan. I have not got the engine back together yet so I can't report on it but he matched the porting to my chambers which is the way to go. I have VM34's for mine. The VM34's are quite a bit lighter too. The cranks can be turned to save weight and make the bike rev quicker but you need to get crank stuffers to do this.

 

[farmer92]

Yeah i read about the lightening the crank, i don't think i want it to rev that much higher though, if it pulls up to 8k or so i will be happy. I was hoping to raise the torque curve all around with a slight bump the rpm range, but hopefully not to much above 6500.

What did you use for chambers?

The general consensus seems to be to go with 34's i guess, that part of the build is still a ways off so i will keep the suggestions in mind.

 

[farmer92]

Maybe i should just get a pair of jemco pipes and run stock-ish cylinders

 

[jimmer]

Lower the intake to the early cylinder specs,34's and the Jemco's and that will be a wide strong powerband! I am a huge fan of flatslides, but they are more money,but worth it in my book.

 

[farmer92]

I suppose this would probably be the safest bet, I really don't think i could build half decent expansions anyway. That will be a project for later in life maybe.
That was my back-up plan and i think going forwards it might become the front runner.
It will depend on what number i get from Jemco as a quote.

 

[teazer]

The "right" way is to set a target for power and rpms and for there work out the port time areas for each port and then design a pipe that matches those ports, but if you have pipes, it all changes and you will find that there is not just one pipe that works for one set of port dimensions.

For your build, you want mild porting without too much intake duration and moderate pipes such as Jemco's Do you happen to have the actual measured port dimensions for your cylinders?