autisa big bore 175cc piston

[lauri666]

hello!


i have had few autisa cylinders for years now and i think i will be finally getting into building an engine with one for my -82 dt.



the first question is what piston to buy? i see that people are using dt/it/mx 175cc pistons but then what year? some of those pistons seem to have ring pins in such locations that they may intervene on the ports.



one of my cylinders is slightly ported and someone took material off of the bottom at some point. saw one thread talking about how u would need to use ypvs crank with this cylinder.



what carburetor size would u guys recommend? i have v-force 4 reeds coming. i have 38mm keihin pwk carb but is that too large? other option would be 34mm mikuni vm. pipe would probably be just regular gianelli pipe or maybe i would get fresco big one exhaust.



so what piston?

what crank?



all tips are welcome!

[cinder]

I run an rd with an autisa cylinder.
I run a yfs200 blaster piston in mine.
Crank can be upgraded with better spec bearings and rod lengths I run an rd350lc conrod in one of my motors and a tz350 rod in the other but as you mention 1gu rod is 110mm so you could a mk3 rod.
Getting the head recut properly is the biggest gain as itll drop your water temp down to acceptable levels.mine are mick abbey tuned to different specs his road tuned cylinders make high twenties when paired with one of his pipes.
I run a 35mm flat side minion mine with no issues

[simon998]

I've mine fitted with 5mm off the bottom so it fit's on a mk1/mk2 bottom end (105mm con-rod). Standard rod, standard big end bearing, ProX Blaster piston, single ring, +2.00mm over so the heads been opened out to 68mm with a larger dome. Currently fitted with a 1GU 26mm carb with 260 main and 30 pilot jet, Ramair foam filter and a Micron exhaust. Not ideal but it's running the very best, rich if anything, and the temp only ever creeps over half when sitting in traffic. Billy Sullivan on Facebook made up a load of quality headgaskets for the big bore kits, he'd be worth contacting to see if he has any left. My dad and I both run them and they are excellent.

I'll get a new 32mm carb and pipe at some stage. I'm currently on standard gearing and it's got far too much lift with the micron (micron makes the powerband @ 6500rpm+), I'm going through gears like a scrambler. It's spinning the clutch from 3rd onwards when it hits the powerband. Thats with heavy duty ebc springs. Going to change the front sprocket for a 17T at the weekend and order up some new EBC clutch plates and see how that goes.

The ring gap will go over the inlet ports. Just got to keep an eye on it I guess. I champered the ports a little extra where they passed to hopefully stop them snagging. Ii'm guessing rings will be a consumable with this set-up - time will tell.

[museumman]

Jun 27, 2022 13:30:32 GMT 1 simon998 said:

I've mine fitted with 5mm off the bottom so it fit's on a mk1/mk2 bottom end (105mm con-rod). Standard rod, standard big end bearing, ProX Blaster piston, single ring, +2.00mm over so the heads been opened out to 68mm with a larger dome. Currently fitted with a 1GU 26mm carb with 260 main and 30 pilot jet, Ramair foam filter and a Micron exhaust. Not ideal but it's running the very best, rich if anything, and the temp only ever creeps over half when sitting in traffic. Billy Sullivan on Facebook made up a load of quality headgaskets for the big bore kits, he'd be worth contacting to see if he has any left. My dad and I both run them and they are excellent.

I'll get a new 32mm carb and pipe at some stage. I'm currently on standard gearing and it's got far too much lift with the micron (micron makes the powerband @ 6500rpm+), I'm going through gears like a scrambler. It's spinning the clutch from 3rd onwards when it hits the powerband. Thats with heavy duty ebc springs. Going to change the front sprocket for a 17T at the weekend and order up some new EBC clutch plates and see how that goes.

The ring gap will go over the inlet ports. Just got to keep an eye on it I guess. I champered the ports a little extra where they passed to hopefully stop them snagging. Ii'm guessing rings will be a consumable with this set-up - time will tell.

I'm glad that guy found something else to do, getting professionals to make things for him.  His advice has been woeful over the years. He's also got posts on FB stating that the YPVS robs the bike of power due to 'restricting the gas flow'  when challenged he says the extra midrange torque you feel on the working ypvs bikes is due to the "longer stroke". He thinks the longer Conrod on the ypvs bike gives it a longer stroke, what a nightmare, loads have tried to argue with him.   His own Autisa bike only made 23HP on the Dyno, the one and only time he's been there,  and that's his lifetimes's work in his own words over the years, now gone very quiet.  Same guy who made "firstly check your woodruff key" go viral on FB when you don't have a spark. Same guy who has a post on there saying you need to lengthen the throttle cable on a MK1 to fit a VM26 (1GU) carb,  yet the MK1 and MK3 cables are the same part number. Measuring inside the carb to the attachment points to carb tops shows why. 

A guy called Leighton on FB had some failures due to the bad advice and understandably keeps things to himself,   he apparently uses a 28mm carb and makes 32HP with Mick Abbey's help. Cost him a fortune though.   
I've had 4 x  Autisa kits from Swiss bikes I broke for parts. All the bores where badly scored. One had the head epoxy resined on with a drop fallen in in the bore. The one I kept still has the head attached with a copper gasket from on a running motor.  I always tried to follow the advice on Facebook for these kits, it was difficult to keep up.

The current competition on Facebook is now installing DT200LC motors in RD's. I'd rather leave them in the DT    Surely there's an alternative 2 stroke motor to throw in there with some clever fabrication to the frame