GT250 build

[Eden]

After ridding my GP all year with a GT200 big block kit bored out to 70mm running a 60mm stroke and enjoying the ride I decided a couple of weeks ago to build another motor using another GT200 kit.
This time I wanted to use a 62mm stroke with 116 rod and use the same H2 piston (71mm) I use in my Italian cast iron 250.

The reason I decided to do this tune was just because the crank I had been waiting for which was a replacement for my Italian cast 250 crank finally arrived and as I already had a spare piston and had acquired another 200 case I decided to give the old 250 a rest until another crank comes along.

The GT230 ive been running this year as most people know was one of the two prototype barrels, I didn't want to do anything more to that barrel so I went about getting hold of the other prototype barrel to use in this new 250 conversion.

Once I had my hands on the barrel and another porcupine head I took them up to Ralph's (Saxalby) for him to do the re-bore and profile the head while I was there picking up the crank. That was the weekend before last 15/11/14.

I then started the porting on the engine case and mag the following Monday night after work and continued working on the motor each night last week.

Its now nearly ready, bar engine mounts, to be fitted into my GP


trench in case for the 62mm stroke



mag marked up....




mag cut




case trans cut




Exhaust port cut, marking up for boost cutting can also just be seen.



Exhaust port finished.



Squishing



Piston marked up



Arc cut



Window cut





Transfers lowered and boost lifted



Marking TDC and various degrees before TDC



Gears and sprockets in





That was Monday to Friday evenings last week. Last night I fitted the clutch, put all the studs in the case and fitted the brakes.

Could have finished it but I need an 8mm case stud, engine mounts and gearbox oil.


Bore and head profiling was done by Ralph, I've done the rest.

Running 62/116 crank
Wossner H2 71mm piston

Cant wait to get it running

[Toddy]

Nice work look forward to seeing how it gos

[steveg]

Thought you did most of your maintenance roadside

Only kidding mate, looking forward to seeing a master at work

[martyn dwane]

Excellent. Love these types of threads.
what gearbox have you decided on and overall ratio
looking forward to "the road videos" or watching tarmac again as my wife calls it .

[Eden]

Steve,, I see myself more as a lucky bodger tbh

As far as the gearbox goes, there is another reason ive built this motor, I wondered how the GT barrel would compare against my Italian cast 250 top end if it had a similar tune, so im using the same final drive and box that has. LI150 gears, 17-47 sprockets giving final 4.7 final drive.
The tune on this in relation to port timing is very close to how my other 250 was before I had to raise the exhaust port a couple of years ago.
For the same reason i'm using a franspeed race on it to start with.

The gears and pipe may well change over the next few months as might the tune in that I may make the blowdown longer.

All depends how it runs and what its dyno graph looks like.

[jonw]

Eden, why 250? What are you looking to achieve? I'm curious as to how your thought processes work on a project like this. Are you looking to create something that gives you an end result or are you just building it and seeing what the end result it gives you? Why do you work around expansion chambers that are already out there and may not suit the characteristics of or reach the potential of your motor as opposed to building the motor then commissioning a pipe to realise the potential of the motor?

A lot of questions I know but I'm just curious as to your starting point. Love these threads by the way and am wholy behind what you are doing.

Jon.

[Eden]

As I said, this is more of an experiment than anything else.
The first barrel I tuned was my Italian iron 250, I did that in stages over 4 or 5 years, learning at every stage, each stage being a change in port timings.
When I first got the chance to test the prototype GT barrel I originally wanted to do the tune that i've just done to this barrel but I was unable to for one reason and another, one being that RIchard didn't want me to bore the barrel to 71mm.

Why 250, well, I already had the piston and the crank because they where for my other 250, I know the piston is the dogs bolloxs because ive done many 1000's of miles on them, however I don't know the crank will hold together and tbh I would rather it let go in any other barrel than my Italian cast 250, just because I'm a sentimental old fool, so you could say im testing the crank is up to the job in the other barrel.

I know I have a very reliable and quite quick tune with the GT barrel running as a 230cc so I'm eager to see how far I can go with a GT barrel, not that ive gone mad with the porting on this new barrel yet, I find doing these things in steps is the best way to end up with something I'm happy with and the best way to learn more.

I have already said elsewhere that the exhaust will probably change, in fact ive ordered a different exhaust but it wont go on the motor till I have the comparison I'm looking to get. Also ive ported it to suit the fran race, because I fits my riding style, but I intend to see what other pipes do to the motors characteristics.

Why do it with a GT barrel? well its cast iron not aluminium!

what am I trying to achieve is the wrong question really. I suppose im testing a few theory's and assumptions and above all im enjoying doing it.

What other reasons do I need?

[Mr G in NYC]

Look forward to the updates G.

[Ken Tucky]

Eden,
Don't underestimate yourself, there's not so many people willing to dedicate themselves to do what you're doing, particularly when it includes grinding cast iron barrrels!
I've been there as you know, and its very laborious (cold even) doing this stuff working in your shed/garage in the winter.
As you say, you're doing it to see what can be achieved, to please yourself, just the same as occurs in racing/sprinting, hope it works out OK, it deserves to, as you are tackling it in the professional way, i.e. not trying to do too much at once.
You have innocently become the road tuner baby!
Richard

[Eden]

Thanks Richard.

I hope it works as expected or im gona look a right tit

[a-teamlambretta]

cant wait to see how this one goes, keep up the good work

[EIBARFAN2]

HOPEFULLY THIS ONE WORKS OUT AS U WANT ! I'M FED UP WAITING FOR U EVERY TIME WE RIDE SOMEWHERE !

[stonerosesmod]

Eden your crazy! But I too love threads like this as its fascinating! Porting timings is a black art to me and im just as bad trying to chase the horsepower with different carbs, exhausts and gearing.What its all about, old school oily fingers and an empty wallet!
Best of luck with it all mate

Neil.

[Eden]

HOPEFULLY THIS ONE WORKS OUT AS U WANT ! I'M FED UP WAITING FOR U EVERY TIME WE RIDE SOMEWHERE !

I was going to put it in the frame tonight but ive been struck down with man flu... truth is I cant be arsed, im having a night sitting by the fire

[Toddy]

HOPEFULLY THIS ONE WORKS OUT AS U WANT ! I'M FED UP WAITING FOR U EVERY TIME WE RIDE SOMEWHERE !

I was going to put it in the frame tonight but ive been struck down with man flu... truth is I cant be arsed, im having a night sitting by the fire

Man flu get your onsie parka on

[Eden]

its alive

Running it on a 30mm for now and I need a new long engine bolt. Started 1st kick

[Dimitrios_231]

It sounds great

[Mr G in NYC]

Its alive !! It Lives !! nice job. G
Now gas it up and gently Thrash it

[gerryjunior]

sounds nice, i hope it runs good for you ,, what stator / flywheel is on it, what did you you time it at ? and excuse my ignorance but can you explain the work on the mag , is it for extra oil, or has it something to do with the crank , thanks i enjoy these treads..

[stonerosesmod]

Is that a franspeed pipe Eden?