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[Admin]

I split the cases and had the crank rebuilt. New seals, main bearings, matched weight on the rods. New pistons, rings...replaced cylinder tie-rods. The builder that ported the barrel cut the gears though I don't fully understand what that meant...sealled the cases back up with YamaBond and tested for leaks.

The engine is a 1974 but we made an adapter for the 36mm carb to fit over the clutch hub.. The carbs were reamed out to 37mm and clutch was rebuilt with barnet plates.

Lots of little stuff done but getting closer. We are welding new rear brackets for the new pipes and replacing the points with an Arctic Cat triple MSD multi-channel ignition system.

[Admin]

The builder that ported the barrel cut the gears though I don't fully understand what that meant....

May mean either:

Put a straight instead of angled gear on the end of the crank to reduce sideways pressure on the crank bearings

OR

Cut the tranny gear faces flat or maybe even angled the other way to reduce popping out of gears.

I'm sure he could mean a few other things too, like re-gearing the tranny to a close ratio jobber.....

It'll be fun when its done!

Good luck - Arne

[Admin]

Arne,

You jogged my memory, the builder said he "under-cut" (his words) the transmission gears. If I remember correctly, he wanted to minimize or prevent the gears from popping out. He did that work back in 1988 so its getting harder for me to remember back that far.

He did a bit of porting work on the barrel but unfortunately, didn't map the new dims. I will map it next time I have the head off. There's no lift-spacer under the barrel. I can see that the intake ports have the bridge removed (except for a teardrop on each end) and it appears there was more work to the lower edge of the intake port than the top. The compression on each cylinder measured 135 psig which doesnt seem like what you would expect for a race engine (even from this period) but I'm told its a good safe number to start with until we get further along on the project and establish good timing and properly jet the carbs among other things.

I started installing the MSD Arctic Cat triple triggers and timing plate and now have to make a definitive decision . If I mount the triggers in the points housing, it seems easier to transfer the trigger mounting holes onto the stock GT750 points plate. We have a spare stock plate and cleaned it off so it is completel flat. There's no interference from existing holes that would get in the way of mounting the new triggers.

The other option, is to install the stock Arctic Cat timing plate within the Alternator housing and making an adapter plate to pickup the alternator mounting holes and attach the trigger plate to that. Then, figure out how to attach the flywheel properly. If I take this route, I can eliminate a number of components on the left side and lighten the remaining parts to continue to run the water pump. I'll have to seal off the points shaft penetration but that shouldnt be too hard.

[Admin]

Undercutting the tranny gears makes them tend to pull themselves toward one another making it harder for them to jump out of gear and also making the shifts lock up much better. The down side is that you will probably need to find neutral while still rolling as it is very hard to get it out of gear when you are not moving. That becomes habit pretty quickly and does not usually cause a poblem.

The intake ports were not bridged originally, they all had the little tear dropped shaped hump but did not have a bridge.

Wayne

[Admin]

Wayne,

All my GT750 intake ports have bridges. Are you saying that some didn't?

I have looked at early J through to A model barrels and so far all have a bridge. I want to remove the bridges in my reed motor intakes and this is the first reference I found so far to removing them.

[Admin]

I have three different motors '74,75, & 76. None of them are bridged on the intake and they all appear to be stock with no port work done. They all just have the little tear drop shaped hump.
I never had an early one apart, so they may be bridged.

Wayne

[Admin]

This link describes the different barrels. If you click on the "See Barrel Diagram" link is shows the bridge. A little lower, there is another link that shows sketches for the intake and they also show a web.

http://smokeriders.com/Technical/Suzuki ... ocket.html

My barrel is a 1974 SN 52205 which I estimate puts the production around July 1974 before the second version was released and it had the bridges. I know the 74 second version (August) increased HP and I wonder if that was the time the bridges were removed.

I think this is a good question to understand better since the difference in intake configuration would have to have some impact on the jetting.

Wayne, I think this is an excellent topic to get to the bottom of. Later today, I'll snap a pic of my intake and post.

[Admin]

The 74 August version you state could actually be the 75 model were HP was increased and the cross-over headers were removed.

[Admin]

This is really odd. I have two L(74) motors here and just rebuilt an A(76) and they have different porting but the same spigot intake with full length intake bridge.

I have a couple of spare barrels and they are the same.

I also lookd at the barrels on Suzukidave's motor which uses a very early set of J barrels and it has the short bridge and flange carb mounts.

A standard tip back in the day was to shorten the bridge down to about 12mm from the liner out into the port. That would make it more like an RZ350/Banshee

Those diagrams came from Dr.Q (Robert Knippleburg (sp?)) who made the squish head conversions, but let's not open that can of worms again.

I can't wait to see the pictures of your intake ports.

teazer

[Admin]

This is a little embarassing guys.

When I went to the shop to look at the Buffalo motor that I have disassembled I figured out the unbridged intakes with the tear drop shaped hump that I was remembering are the ones for the H2 motor I'm working on.

The cylinder I have for the GT750 has a full bridge just like everyone else's.

Sorry for the confusion I caused.

Wayne

[Admin]

Wayne, I went and took a better look at mine tonight too...here is the LH intake on the '74 cylinder. No teardrop at the bottom. Only on top.

[Admin]

WOW! That has been hogged out A LOT. If the rings don't catch on the edge of the port, it ought to flow way more volume than stock. There is probably almost twice as much total area in that port as stock. I guess it also depends on whether the speed of the incoming charge is moving fast enough to utilize the available volume.

Wayne

[Admin]

Thanks Kevin,

That is a stock GT750 barrel with bridgeed inlet which has been ported. they have left the "teardrop" to support the bottom ring that may be exposed in the intake port.

That's good in that I understand what happened to that barrel, but I need to understand Wayne's barrels too. It sounds like his are dfferent in some way.

[Admin]

Richard,

Here are some images of the MSD Arctic Cat triple flywheel. The taper measured 17mm on the front and 23mm on the back edge and thickness is 30mm. I didnt get a chance last night to try it out on the crank but I'm sure it will require a lot of luck to have it fit without machining.

[Admin]

Kevin,

Those dimensions look to be a perfect match for the GT750 crank. A Polaris triple by comparison is 23mm rising to 27mm over 40mm.

The nose on a GT750 crank is about 18mm to 22mm over 27mm length, so your Arctic cat rotor may just slide straight on. try it on a crank in a set of cases without a stator and see how far in it is from the surface that you would mount.

You could have struck gold there young man.

Teazer