GT240 Build

[coaster]

Hope you don't mind me posting on here but what oil ratio is recommended? I assumed 3% and have been running with that so far on mine.

[eden]

I would recommend 4% due to the boyeson feeds diverting fuel charge away from the big end. Same as an RB!

[coaster]

I would recommend 4% due to the boyeson feeds diverting fuel charge away from the big end. Same as an RB!

That's a bit worrying as it will make a significant difference to the oil required to get to Adria and back Don't other boost ports do the same, TS1, Super Monza etc. Also, the GT is a lower revving motor so would the crank be under the same load?

Just clutching at straws really, we will only be running at 55ish mph

[Darrell Taylor]

lots of modern 2 strokes and oils are lubricating as low as 1% on extreme high performance mx motors regardles of cylinder reed or case reed design there puddle/mist lubricated anyway and the main direction of flow thru reed is still thru centre ,i dont buy into the boyessen fed need more oil % but AS IT HAPPENS will naturally get more oil anyway due to longer delivery periods as witnessed by the richer jetting requirements they are often 10% richer in practice ,although on some cylinder designs they have an almost impossible route thru the boyessen feeds either being blocked by the side of the reed itself or the reed flow direction over delivering to one side but either way its straight thru into the case over top of crank.On a good oil many run 2 % with no issue although i prefer a safer 3% on high end motors ,upon stripping a motor you will know how the oil ratio is doing by rotating the crank to see the oil puddle covering the webs as quite a lot sits down there ,you can also spot the oil quality ,if black or dark its often broken down to a point its failing ,a good oil appears as it does out of the bottle,very reassuring to see. and the lower % returns some value back to the generally more expensive products.

[eden]

I would recommend 4% due to the boyeson feeds diverting fuel charge away from the big end. Same as an RB!

That's a bit worrying as it will make a significant difference to the oil required to get to Adria and back Don't other boost ports do the same, TS1, Super Monza etc. Also, the GT is a lower revving motor so would the crank be under the same load?

Just clutching at straws really, we will only be running at 55ish mph

I have the same predicament for the euro.
I for the trip I will be doing the same as I do on every long euro trip I've done on the GT top end. I will be alternating my % at each half tank fill up.
I know your using groundsman and I wouldn't worry about what Darrel says above.. I'm sure you have stripped your motors which have run on groundsman and seen the red oil covering all internal parts below the piston crown.
Your fuel consumption will be low enough on your GT kitted lambretta to balance out the 4% mixture... I've worked out that for the 3000 miles I'll hopefully be doing over the euro trip that I will need 10 litres of oil... I'm taking 12.

[eden]

Coaster, I've tested the boyeson feeds in the gt200 kit.
I ran an early one with a piston that had nothing cut from the skirt and had no reed windows. This piston gave short inlet timing under the piston but the boyeson feeds still gave 360 degree induction controlled by the reed. In this configuration most of the charge had to traverse through the boyeson feeds which connect dirrectly to the transfer ports in the batrel.
The result was that the engine ran fine and had good power.... however the big end on the crank failed after around 4000 miles
.
I base my beliefs on the results of real world testing over distance on the road rather than gut feelings.

[coaster]

Thanks for the replies guys

[Darrell Taylor]

i have a new customer who also tested a boyessen fed gt kit who had his crank fail at his recommended 4% at less than 1000 miles so does that individuals experience identify that 4% is not enough ,there is no relevance to the oil % used in this instance or yours eden to oil % ratio and crank lifespan there either badly assembled or just failed thru exceeding there service limitations at there relevant performance level .Then a racers crank i viewed at af on saturday which had less than 1 race under its belt on top quality oil will this be the oil at fault or the crank or the build ? ,fact is a single experience although valuble is less than multiple owners of 50 to 100 over a year to gauge a trend. The super monza , casa ss200 ss225 ,rb 20 rb225 rb250 all are boyessen fed and many owners i know run on various oils and % ratio,s as low as 2% to high mileages without issue ,the fuel oil mist delivers via the various methods filling the case prior to transfer opening creating a fully stuffed fuel oil mist within the whole area ,it doesnt decide to take a look at a conrod/big end area and keep its distance

[Darrell Taylor]

Coaster, I've tested the boyeson feeds in the gt200 kit.
I ran an early one with a piston that had nothing cut from the skirt and had no reed windows. This piston gave short inlet timing under the piston but the boyeson feeds still gave 360 degree induction controlled by the reed. In this configuration most of the charge had to traverse through the boyeson feeds which connect dirrectly to the transfer ports in the batrel.
The result was that the engine ran fine and had good power.... however the big end on the crank failed after around 4000 miles
.
I base my beliefs on the results of real world testing over distance on the road rather than gut feelings.

so in this singular instance you conclude that a 4000 mile crank fail was due to reduced delivery through the inlet port due to lack of windows or skirt cutaway ? ,,every rotax 122 and 123 motor 125cc run this way at very high bmep figures by 100,000 plus mostly mechanically unsympathetic riders of this learner legal machine at around 30bhp 11000 rpm and in many race series around the world in proddy racing and kart racing to no ill effect designed and developed by rotax engineers of the finest 2 stroke powerplants with extensive r and d departments , thats not gut feeling thats interpretation of real world testing on mass not the findings of an individual.

[Darrell Taylor]

I would recommend 4% due to the boyeson feeds diverting fuel charge away from the big end. Same as an RB!

I have the same predicament for the euro.
I for the trip I will be doing the same as I do on every long euro trip I've done on the GT top end. I will be alternating my % at each half tank fill up.

? why would you alternate per half tank eg 4% then 3% leaving 3.5% average and not fill all at 3.5% then quote straight 4% to others .As part of THIS alternating presuming fill up distances wont be exact dependant on station locations will fueling be adjusted to suit the leaner at 4% richer at 3% scenario.
really is overcomplicating a simple process