GT550 Cafe project

[ja-moo]

If it's not too late, it would be interesting to see how much the engine assembly weighs?

[imquattro]

I will weigh it tomorrow.

[imquattro]

So I cleaned up the "RAM AIR SYSTEM" badges. I sprayed them with gloss black engine enamel, then using 800 grit paper, I removed the layer of paint on the raised letters. I then polished them and sealed them with clear engine enamel.
I think they turned out pretty nice and saved me some $ from buying a set.


I had scotch padded the top ram air cover and then polished it on the buffer. The casting quality wasn't great and theres some porosity that shows up when it's shiny. The buffer system I have isn't the best, but it's worked pretty well so far. I wish I had the determination to break out the dremel buffer and get every nook and cranny but I don't. I have to draw the line somewhere.

I then assembled the badges into the cover, and after blasting the heads of the old fasteners & refinishing them in the same black gloss enamel, bolted it all together.







The orange hoses you see at the bottom of the last picture are silicone vacuum tubing for the SRIS. Problem is, and I found this out after purchasing it, silicone of this type swells in the presence of hydrocarbon based liquids. Bummer. So, I guess I'll have to bite the bullet and go OE for those after all. (Tubing was 1.115" ID and was only $13 for 10' from NAPA, should've just bought the real deal, I know.... sigh)

[ja-moo]

I will weigh it tomorrow.

Cool!

[oldjapanesebikes]

The orange hoses you see at the bottom of the last picture are silicone vacuum tubing for the SRIS. Problem is, and I found this out after purchasing it, silicone of this type swells in the presence of hydrocarbon based liquids. Bummer. So, I guess I'll have to bite the bullet and go OE for those after all. (Tubing was 1.115" ID and was only $13 for 10' from NAPA, should've just bought the real deal, I know.... sigh)

That engine is looking very sweet !

I know from personal experience that hind-sight is always 20/20 , and it won't make you feel better, but the OEM hoses would have actually been cheaper (3 times $4.20 each).

[Coyote]

It's already doin' a 100! There is a ground wire that runs from the forward most center shroud screw to one of the coil mounting bolts. I have a spare if needed. No charge.

[imquattro]

I know from personal experience that hind-sight is always 20/20 , and it won't make you feel better, but the OEM hoses would have actually been cheaper (3 times $4.20 each).

True...sigh.

[imquattro]

There is a ground wire that runs from the forward most center shroud screw to one of the coil mounting bolts.

You mean this one?


Got one.
Thanks for the reminder on location.



Here's the spare pack from the '72 (boots removed from plugs so it'll work on the '74's ram air shroud.)




They've both been blasted and then sealed with clear. Look like new imo...

[imquattro]

I will weigh it tomorrow.

Assembled GT550 L engine (dry, no gear oil) weighs 157lbs

[ja-moo]

I will weigh it tomorrow.

Assembled GT550 L engine (dry, no gear oil) weighs 157lbs

Thanks for that!

[jeff g]

Prior to calling these 100% accurate, let me toss in this disclaimer:
It may not be: It's a paper wheel, a homemade pointer, but hopefully close to within a degree or two.
IF someone would PLEASE check these out, I'd really like to get these right.
I found NOTHING web in all the searching I've done & while someone here thought they had some somewhere, they have yet to show up.
So here goes:

I then rotated the crankshaft until the exhaust port opened @97°. I then zeroed the wheel and rotated the crankshaft counting the number of degrees the exhaust port was open until it closed (open for 163°)
I then followed this procedure for the intake port, and transfer port, jotting things down:

Didn't have colored pencils, but if you look real close you can see the semi-circular sweeps inside the hash marks indicating the port openings.

Bottom line:
GT550 Port Timings::drum roll::
One crankshaft revolution = 360° (duh)
Exhaust Port Timing: Opens @ 97° ->to-> 260° (open for 163°)
Intake Port Timing: Opens @ 285° ->to-> 72°AfterTDC (open for 147°)
Transfer Port Timing: Opens @ 120° ->to-> 240° (open for 120°)

If there are any corrections needed, please let me know.
I'm hoping the help out the next guy...

Ports have to be open for an even number of degrees...If the exhaust opens at 97 atdc then it closes at 97 btdc, for a port duration of 166 degrees.

I've worked up a set of pipe specs that should make for a streetable pipe, though it might be a bit tough to fit (bellies are BIG)

TZ...depending on the software that you use, depends on how they want the inputs measured. Of the 2 programs that I have, one asks for port opening in degrees and the other asks for port duration in degrees.

Jeff

[greasemonkey]

did you play with your "midsection factor"?
you can make your pipe a decent amount thinner, changing this shouldn't make much difference in performance and powerband.
I'm not an expert on the matter but my trusty "bell 2-stroke book" never lets me down

[jeff g]

did you play with your "midsection factor"?
you can make your pipe a decent amount thinner, changing this shouldn't make much difference in performance and powerband.
I'm not an expert on the matter but my trusty "bell 2-stroke book" never lets me down

Yeah, I cut back on the beer, eat better, the job has me exercising regularly, but I've still got a big belly.

As for the pipes, I can make the belly thinner, but that changes the length also. Thinner pipes as a rule of thumb reduce the power and narrow the torque range. In other words, you'll have a little less power, a more sudden powerband, and torque starts higher in the RPM range.

[greasemonkey]

did you play with your "midsection factor"?
you can make your pipe a decent amount thinner, changing this shouldn't make much difference in performance and powerband.
I'm not an expert on the matter but my trusty "bell 2-stroke book" never lets me down

Yeah, I cut back on the beer, eat better, the job has me exercising regularly, but I've still got a big belly.

As for the pipes, I can make the belly thinner, but that changes the length also. Thinner pipes as a rule of thumb reduce the power and narrow the torque range. In other words, you'll have a little less power, a more sudden powerband, and torque starts higher in the RPM range.

I know this but at some point you need to make compromises, with powerband I meant the surface under the curve.
will take some more lessons at my pipe maker. (PPS pipes, former spes and doma 2-stroke)

[jeff g]

I almost forgot.

When you put chambers on a GT550 (or if you block the crossovers on the stock pipes) you MUST rejet all 3 carbs with the same size main jet. If you follow the stock scheme of going 1 smaller on the center cylinder, you'll cook the piston in the center cylinder. You'll probably have to start in the 105 main jet and 30 pilot jet range and work from there to get it jetted right.

Jeff