"Pork Chop" Cranks for GT/TR750

[tz375]

Dave,

That's an interesting paper that I have read several times. It was published back in the sixties when Suzuki were doing a lot of research on the subject.

One conclusion was that a small versus large crankcase volume made little difference to discharge ratios and changes to exhaust and intake were more significant.

The research behind that paper was conducted at relatively low rpms and makes no reference to the spread of power at higher rpms.

Suzuki at that time were increasing the primary CR as a means to push the gases out of the transfers and that resulted in narrow powerbands - Ray Battersby (sp?) has a good reference in his book about that.

It was later realized that exhausts do more to "pull" gas out of the crankcase that high primary CR does to "push" gas out. If you look at the many good snowmobile articles written by guys like Kevin Cameron who has forgotten more than I'll ever know, you will see that most sleds have relatively huge crankcase volumes and often use reed spacers which add even more and they are achieving power outputs of 200hp from an 800cc twin or triple.

Bottom line is that you need a crankcase volume that is much larger than combustion chamber volume to achieve good power output over a large range.

BTW, the same authors published another related article if you are interested.

[Suzukidave]

Hi Kris , any updates ?

[Kris Bernstein]

Sorry Dave, busier than a one armed tuner! Got the Electrix World CDI last week for the right side crank nose set up. A very tidy and well put together ignition. I remember how spotty the quality control was on the old TZ units from Femsa. It was nice to see liquid tight connectors used on this unit. Also comes with all the fasteners to mount the unit to the cases! Will most likely change these out for titanium bits but it was good of them to provide um'. The coils are amazingly small and light. Wonder where all the windings went to but we'll see how it works soon. Absolutely no printed instructions came in the box from the UK. They can be downloaded from the web site but it would have been nice to see them on paper.
The stater magnet used a double taper (female-to-male) to adapt the standard Electrix World stator magnet to the GT 750 crank nose. I used one like this provided by NOVA to adapt the TZ stator to the T500 crank nose, so I could run a Femsa unit on those motors when we raced them ages ago. I never had any problems and sometimes ran the 500 motor to 10,000 RPM when necessary. However I know of at least one set up where the female-to male taper failed and destroyed the stator in the process. We'll see.
Pictures to be posted this week.
Deeply saddened to report an inspection of the Applebee Pork Chop crank reveled a bent rod from the damn shipping gorilla's at UPS, so the crank is back in the UK for a rebuild with ZERO f.....g miles on it...
All be well,

Kris

[Suzukidave]

Nice parts pile your building there Kris , no bodgering there ... too bad on the rod but extra good you noticed it .

[Kris Bernstein]

Yea, that it so far....just cash out and nothing ridable.
Started milling the cylinder for the spacer plate that goes underneath to raise the porting. Also got the intake spuds milled off but haven't "hit water" yet like on yours. Sending the head out this week for squish band inserts and some other stuff. The pile keeps growing....

Kris

[Suzukidave]

Yeah , now that i have milled of the intake side of one block i will try not to make that same mistake again . I sure know the feeling of spending a bunch on part just to still not have it running , but to be honest thats my fault as i now have most i need to finish the job .

[Kris Bernstein]

I'm doing the mod on an early barrel without the "water cooled" decal. The ports are easy to do once the top of the head is milled the thickness of the spacer plate, I'll take a picture of it and post it too. Pretty simple to fab and makes the porting job easier...except for the reed intakes!!!!

Kris

[Suzukidave]

Yea, that it so far....just cash out and nothing ridable.
Started milling the cylinder for the spacer plate that goes underneath to raise the porting. Also got the intake spuds milled off but haven't "hit water" yet like on yours. Sending the head out this week for squish band inserts and some other stuff. The pile keeps growing....

Kris

I didnt get into trouble until i went further than this

[Suzukidave]

But to get even closer in to the bore i didnt know that the water jacket was just above the intake opening , so if i had dropped down to the lowest point i needed to cut down to ( the level of the stud passageways ) and cut my way up till i just cleared the intake ports i could have not cut into the water jacket but you can see its very close .

[Kris Bernstein]

Yea, there you go Dave, great pictures as always.
My cylinder is a ' 73 as it has no decal and does not use the Mikuni style intake rubbers. So I was able to get flush with the upper part of the barrel "fins"
but don't dare go any deeper on the passes with the mill. Was wondering if anybody would be interested in some 75mm Weisco pistons to make their motor's "850's"?
I am going to check with them on minimum production runs and will need to have twice as many left/center pistons made. They will require aluminum sleeving but that will allow for porting changes and use of a single ring on a Nikisel bore. Heat transfer should be better once the iron sleeve is done away with. A quick hone to break the cylinder flash and three new rings will be necessary every so often. Being a race motor mine will get new rings every three race meetings. Don't think flat top pistons will work with the crude porting, so domes might be the way to go.
What say you?

Kris

[Suzukidave]

Kris, dont you need to get the reeds in closer to the bore ? I thought it was best to get the reeds in as close as possible to get the best signal from the intake pulse and that will take you milling down like my second picture .

[Suzukidave]

Here is a picture of one of the later type blocks machined for reeds , but also on this one it was cut just a bit to far in and broke into the water jacket

[tz375]

That's a very Butch looking block.

Did I send you pics of the second block I had machined? I found that in order to get the reed blocks in close enough and at a suitable angle, there is no way to avoid breaking into the water passages. They have to be welded up but there's so much other welding to be done that it's not an issue.

Kris, are you planning on revving to more than 10K? Single ring pistons appear to lose HP below about 8 or 9 k and make more above that, so a single ring piston is not suitable for my needs.

Depending on skirt thickness, you may be able to get away with pistons without transfer cutaways and use a template like Ocelot did to cut them yourself.

[Kris Bernstein]

Yes, Chris Applebee indicated that the Brit grass track racers regularly rev them to 10K and I can see it happening if the pipes will not fall off.
Does make sense to use a templet and mill them myself. If their is enough interest we can do two ring pistons and I'll live with that. My concern is pin location as the intakes will be raised very nearly to the ring at BDC, but we'll have to see how it plays out.
What manner of templet do you suppose they used?

Kris

[tz375]

They had a steel ring/tube that was slipped over the piston and located with a steel pin through the wrist pin boss.

i have a picture of it on the PC with the crashed flat screen monitor. I'll see if I can swap out a monitor from another PC and dig that file out for you.