RD370cc big bore (relined from 250 barrels) comparison pics

[Jbretel]

This is for anyone interested in the 370cc conversion (relined 250cc barrels):

Barrels just back from Ron at Fahron Engineering:

Direct comparison of a std 250 barrel to a relined/re-sleeved and reported Fahron Engineering 370cc 66mm bore barrel ................ WOWZERS



Exhaust Ports compared:-



Inlets comparison from the bottom:-



From the bottom - woweee



More inlet and transfer shots



Exhausts and transfers



More lower barrel shots



more inlets - everyone loves photo's eh?



370cc transfer side'ies



250cc side'ies



370 inlets



250 inlets



Camera battery went flat before I could snap the reprofiled head so I will edit this thread over the weekend to include the shots of Ron's work on the head.

EDIT:-

Here they are (Pics of the reprofiled head)



Bit blurred - maybe coz I had too many ciders last night - heh heh!



End of Edit


He's gonna probably curse me know - as a deluge of you rush to convert loads of old knackered/scrap 250 cylinders - hahahahahahah

Nice for sleepers if you keep the 247cc on the outside of the barrels mine will be engraved with the new cc and Fahron somewhere - as my bro' in law is a jeweller

Fab work for £400-450'ish (including new proper Mitaka 66mm piston kits and reprofiled 250cc head work) - I can't be exact as I had some other work done on

The transfer ports came back very sharp (which Ron says is fine) but I think I will chamfer them back 0.5/1mm at 30 degrees, as recommended by some top US two stroke experts (saves ring snag when super hot as they try and expand into the ports) especially when breaking in the engine - but I welcome peop's thoughts on this.

I have some tuned reedblocks with dual-stage Boyesen reeds to go on this, and maybe the big fack-orf K's you can see floating around in the background.

+ some 6mm carb/reed spacers as well.

Oil pump is off to be refurbished and uprated for low revs delivery by Arrow from here shortly - then it's time to put it on the freshly rebuilt motor and run a few heat cycles - whoop, whoop!

[steve h]

It would be neat if you could get them working off the orig 4L1 carbs. It would certainly surprise a few folk with the extra ooomph
247cc still on barrels?

[Eyrey1]

my mate has one with swarbricks on
still says 4l1 247 on the barrels ,its pretty quick and has a
good bit of torque as well a good bit more than the std 350 does
i think all 250 barrels should have this done to them !lol

[yazza54]

Nice work and not too expensive

[350wayne]

You've gone and done it now ! I was thinking about having this conversion done on a 250 motor to put in my tzr project and now that I've seen these pics I'm DEFINATELY doing it !!!! ( there goes the budget ) all I need now is a good 250 motor ......

[smokin074]

Wow

[steeley]

nice work there ,you will have to post up a dyno graph when you have run it in.i have got a set of knackered barrels and head in my shed interesting.

[andygasgas]

Can't wait to see results when up and running got 2 spare sets of 250 barrels and heads gathering dust mmm

[fatfastroger]

Great pics - just shows how poorly finished the factory castings were, guess thats mass production in action at a price.
Should be a strong motor in the end.

[yazza54]

Jun 20, 2014 2:30:52 GMT 1 350wayne said:

You've gone and done it now ! I was thinking about having this conversion done on a 250 motor to put in my tzr project and now that I've seen these pics I'm DEFINATELY doing it !!!! ( there goes the budget ) all I need now is a good 250 motor ......

Haven't you got a 350 anyway to use?

[Norbo]

They look great mate \rod allways does a top job when they get done LOL

[copper99]

Lovely work..

[db8888]

any pics of the pistons really nice job on the barrels

[spooch63]

Think they're good for 4 rebores

[spooch63]

Currently looking for a set of barrels myself so i too can blow the budget and timescale out of the water !!! Amazing how a 6 month project can turn into 12 months then 18 and we all now the rest !!

[steve h]

2mm worth of re-bore potential. Mitaka Yam blaster pistons.

[bare]

A LOT of expensive man hours turning 250barrels into Ersatz 350's. Why?
That's an Odd approach considering the downsides of a re sleeve.
Regardless, DO rethink fitting Trap door Boysens.
IMO you might as well only fit a plug to one cylinder.

[andygasgas]

Bare do u ever say anything other than criticise what others are doing ? Just thinking out loud lol when u consider the price of a set of 30 odd year old 350 barrels if u can find some then possibly a rebore etc it's not that much more and as 250 barrels cost a 1/3 the price it's even better

[steve h]

A pair of 250 barrels can be had for a little over £25. Inc postage.

[lcyoungboy]

After seeing this I am definitely thinking of going down this route..keep us updated

[yamark]

I'm well impressed with the work. Warm glow knowing my 4LO can live forever!

[Jbretel]

Jun 20, 2014 20:03:38 GMT 1 db8888 said:

any pics of the pistons really nice job on the barrels

They are std 66mm Mitaka Yamaha 200 Blaster pistons - but slightly modded on the tangs see below:-

[Jbretel]

Jun 21, 2014 2:41:30 GMT 1 bare said:

A LOT of expensive man hours turning 250barrels into Ersatz 350's. Why?
That's an Odd approach considering the downsides of a re sleeve.
Regardless, DO rethink fitting Trap door Boysens.
IMO you might as well only fit a plug to one cylinder.

Its a better proposition than forking out £300+ for a set of std 350 barrels (I was looking for quite a while).

Plus the wider bore and optimised port work and revised timing give better torque characteristics than a tuned 350 (read : Accelleration ) and after doing a fair amount of research last year, I realised this was probably the best proposition for what I had in mind (a 4l1/0 "special").

I have some spare YPVS units, one with a +4mm stroker motor that is mildly tuned, which will probably go into the second 4l1 frame I have (or the Mito or the 3MA .....// and running gear will be a Gixxer6 SRAD RWU forks/triples with CBR400RR NC29 swingarm and wheels etc)

But this one is being built to reflect a special that would have been built circa 1980-82 so YPVS engine was not even considered an option.

& value / money never really came into it, although its a fab job for the actual cost

It's really just been done "because it can be" and will set it apart from other specials (not "better", just "different") ..... I like different ....... I'm a bit "different" - ROTFL

Dual Stage Boyesen have a mixed feedback - I'll suck 'em (or rather they will) and see - I have others (fibreglass etc) so it's all about the tinker and tweak, till the best combination is worked out - ditto the reed spacers 6mm/8mm/10mm etc.

And of course I have the 34mm PJ's - which'll sound awesome but probably make it totally unrideable - #smirk

Right .................. off to the Pub for my little bro's 40th B'day bash - should get pretty messy so won't be responding until mid afternoon tomoz.



Ciao Bella's

JB

[steeley]

so is this right what I am reading ,no more lc hybrids. hmmmm I don't think so. Interesting project though .think I will dig that 250 lc top end out of the shed and put it on the bench under future project.

[marsbar350]

see where you have taken the tangs off the pistons
file marks still evident.get some wet and dry and smooth the file marks out.could start stress cracks in em

[yazza54]

Anyone got fahrons contact details ??

[marsbar350]

Jun 21, 2014 22:28:25 GMT 1 yazza54 said:

Anyone got fahrons contact details ??

yes mate

[yazza54]

Can I have them then lol or just send them to smads

[Jbretel]

Jun 21, 2014 19:51:38 GMT 1 steeley said:

so is this right what I am reading ,no more lc hybrids. hmmmm I don't think so. Interesting project though .think I will dig that 250 lc top end out of the shed and put it on the bench under future project.

I am building an LC/YPVS hybrid (next) - just that this one I wanted to be an auld-skool special - circa 1980/1/2 - raask rearsets, allspeed pro-bars std wheels etc etc - not standard but nothing too modern/trick either.

The Hybrid will be another thing entirely (see my other posts on this)

Ron's number (at Fahron Engineering) is 0115 963 4123 and just say you saw my thread (Jeremy from Guernsey) on this forum - there's no discount benefit (he's too busy as it is) but just nice to let him know where he's getting the trade/feedback from

Better book the barrels in for conversion in 2015 though - lol.

J

[Jbretel]

Jun 21, 2014 20:37:01 GMT 1 marsbar350 said:

see where you have taken the tangs off the pistons
file marks still evident.get some wet and dry and smooth the file marks out.could start stress cracks in em

Cheers Mars - the barrels trf ports have to be chamfered as well, so I'll do these at the same time.

Another point to note is that these pistons need to run 350 top end bearings NOT 250's

Has anyone got any feedback on running the silver plated one's (Norbo has some I think) vs small end standard bearings?

Cheers,

JB