Easy. Anneal the copper, Assemble the motor without base gaskets. Try pushing it up and down the drive in gear - perfection.Originally Posted by TZ350
Bucket Racer/Crasher
Easy. Anneal the copper, Assemble the motor without base gaskets. Try pushing it up and down the drive in gear - perfection.
Forum whore
Because a few people have asked about the GP engine, to save wading through 270 pages, these links go to the more relevent posts about the 27hp engine. Different link collections can be found on the decade pages 80-90-100.....260 etc.
27rwhp 1978 Suzuki GP125
The oiler holes for the exhaust bridge need plugging on most pistons so they can be used in the GP's. Normally I would weld them but was persuaded to try gluing them with some super duper stuff that’s as tough as shark shit.
Forum whore
BF=(A/B)*100
A is the flywheel counter balance weight and B is the reciprocating mass (weight).
The lower half of the rod and big end can be considered rotating mass and disregarded and the upper half and little end reciprocating mass, along with the complete piston assembly.
Ballance Factor in % is A/B * 100 and is the amount of reciprocating mass counter balanced by the flyweel counter balance weight.
Finding "B" the reciprocating mass. 231.9g
Finding "A" the flywheel counter balance mass. 73.4g
In this example BF = (73.4/231.9)*100 = 32%
A will need to be 231.9 * 0.55 = 127.5g for a balance factor of 55%
Adjusting "A"
This crank needs some mass added to the flywheel counter balance and this is being done here by removing mass from around the pin, and that effectivly makes the counter ballance heavier.
There has been a lot posted on ballance factors, you can use "Thread Tools" / "View Images" to find them.
Forum whore
27rwhp cylinder
Cylinder Deck Height (Squish) 0.8mm.
Exhaust 25.8mm from top of cylinder, and opens 80deg ATDC for 200deg Duration, 75% of bore diameter.
Transfers 40.8mm from top of cylinder, and open 116deg ATDC for 128deg Duration.
Mains left std with the port roof angled up 12 deg. Boost std at 55 deg, and all opening together. Primary transfer pretty much std., secondaries and boost as wide as possible.
Wobbly suggests having the secondry transfers opening 0.5-1mm after the mains. He also points out that the port that opens first, flows last as the residual gases in the cylinder pushes down into the transfer duct before there is enough vacuum in the cylinder to allow the transfers to flow.
Opening the rear transfers and boost port. Flatten the port roof of the rear transfers to 5 deg and leave the boost at 55.
The copper under the exhaust port is to quickly transfer heat from this area to the copper under cylinder cooling fins.
The copper fins get realy hot, and that is heat from the exhaust port that is not getting into the cylinder and the rest of the motor, with this copper, the cylinder and cases run cooler.
The copper is a bit optional, the real performance comes from opening up the rear transfers and boost and increasing the blowdown time area by rasing and widening the exhaust port.
Don't forget to leave ring friendly radiuses in the corners of the exhaust port like this Aprilia. The Suzukies single exhaust port limits blowdown-time-area and power. For the Suzuki GP to make any power the secret is to keep the transfers as low and wide as possible and up the area of the exhaust port that is above the transfers.
Forum whore
CCing the Cylinder Head ........ looking for 13.5 - 14.0 to 1 compression ratio, thats about 9.75 - 10cc clearance volume in the head.
CR = (CV+SV)/CV
Compression ratio = Clearance Volume plus Swept Volume all divided by Clearance Volume
We use car anti freeze and 5 and 3 cc syringes. Plastic syringes can be brought from the Chemist.
With the volume in the copper head fin and concave piston measured we only needed 6cc in the head itself.
Piston at TDC and a light smear of grease to seal things, the clearance volume was measured. It took a few skims in the lathe to get it right but in the end it was spot on.
F5Dave mentioned he takes the level up to the second thread (I think ) in the plug hole to take account of the volume inside the spark plug. If your running a 50 or even a 100 or 125 small volumes like the inside of the spark plug matter.
Works a treat.
Forum whore
Early Honda RS Pipe ...........
The early RS pipes can be made to fit on the Suzuki GP realy easily. The original flange needs cutting off and another made, I used the one off the original Suzuki GP pipe.
The Suzuki exhaust port is 36mm and the RS pipe is 40mm, we don't match them up, we leave the step, we think it helps attenuate (hold up) the return pulse and broaden the power spread a little. Who realy knows, but Honda have a similar step in their RS barrels.
The mid section needed cutting and turning. We used braze on this as it copped with the old oil better than the tig, also the copper is a softer join with more "grip area" so less likely to crack.
The RS pipe dimensions if you want to make one of your own. The venturie at the end of the reverse cone means you don't have to worry about the length and diameter of the stinger. With a blead down venturie, make the stinger diameter bigger and its removed from the resonant equation and then just becomes an exhaust pipe.
Forum whore
You should cut the plug surface such that the unthreaded end of the plug body protrudes 0.5mm into chamber.
With a 10 range plug, then the vol to top of the plug hole is exactly 2.2cc bigger than the chamber.
I use ATF in a burrette, no grease on the bore as you want to measure the above ring crevice vol as well.
Find tdc, then drop the piston a small amount - fill the vol to 1/2 way up the threads, move the piston up/down, till fluid sits the highest,then fill to top.
Leave the burrette sitting for 5 mins as the fluid left on the glass walls slowly runs down.
While this is happening you can take off the head and clean things out.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
Moped rider
I’m not a regular on this forum but do have the occasional read. I note that this thread (& some others) have made the occasional reference to my Derbis. So I thought some of you might be interested in a bit of background. Its a long post, so pass over if you have a short attention span...
Bucket racing for me began in 1987 with an MB50 at Ohakea. I moved to Auckland in 1989 & then replaced the MB50 with an RG50, then fitted a TS100 engine into another RG50 frame in 1992 to race F4 as well. The RG50 was replaced by a TZR50 in 1992, & the RG-TS100 was replaced with an MB100 in a TZR50 frame in 1996.
I have always done my own 2-stroke motor work (outsourcing some welding & machining – mainly to RMS engineering) & first went near a dyno in 1996. My TZR50 made 14 RWHP & my MB100 made 25 RWHP on a Dynojet 100, & that was 15 years ago! I kept racing both those bikes for around 10 years, but in 2005 fitted a Derbi 50 motor into the TZR frame. This still only made the same 14 RWHP, but I did succeed in giving it a better mid-range. Meanwhile I had detuned the MB100 to 20 RWHP in a futile attempt to make it easier to ride round the Mt Wellington kart track...
In 2005 I managed to push through the rule change to allow 150cc 4-strokes, changing the face of buckets by allowing hoards of FXR diesels into the class (& probably saving it from extinction!). Meanwhile I had slotted an FXR150 motor into the trusty TZR frame. This only made 18 RWHP on the dyno, but because the power/torque spread was so wide, it was just as fast as the MB, at least on a kart track, & especially in the wet. By then was also getting tired of replacing cracked crankcases on the MB. From this time on the only dyno I have been near is John Connor’s. I understand he has calibrated it against a Dynojet, but I’m not 100% sure how equivalent they are.
But the diesel did not prove as reliable as I’d expected (over-rev big-time blow-up on the dyno, broken rod & failed big-end all cost a lot more to fix than the good old 2-strokes). So I decided to go back to a 2-stroke & eventually settled on up-sizing the Derbi 50. It is available as a 70 or 80 in some markets, & while 80cc (actually 78cc) is well short of the 104cc class limit (& not much more than half the 130cc air-cooled limit), a modern motor design should go some way to making up for its lack of cubes, plus its light, more reliable & parts are not expensive. Given the potential legality issues with after-market parts, I made sure I used only motor parts (other than ignition, carb & pipe) made for road use. I chose a street Malossi 50mm cylinder (not the alternate MHR team cylinder also available) to go with the 40mm crank. I bought my 1st motor from Corsa wreckers in Mt Wellington. It was already 70cc, but Rick also had a Malossi 80cc cylinder available so I bought that as well. Without going into too much detail, I kept the port timing mild (132 transfer & 193 exhaust) to ensure it would be rideable around a kart track & then shaped the transfers & exhaust to mimic a Honda RS125. Ignition is PVL & carb Keihin PWK28.
This initially made the same 18 RWHP on John Connor’s dyno as the FXR had, though obviously way less mid range torque. In that form my then 15 year old son Nathanael did 1m26 sec lap at Taupo to qualify on pole for the 2009 GP. It was only his 2nd ride on the 80 (I was out that year with a broken back). Unfortunately the new piston I had fitted before the meeting broke on the 1st lap of the GP – it turned out to be the wrong part! For 2010 some refining of the porting increased the output to 20 RWHP, plus I build a 2nd 80 with a few improvements that made 24 RWHP. However the jetting for that run was too lean & it seized in its next race, damaging the bore. I doubt it makes more than 23 RWHP currently. We had high hopes for the 2010 GP, & while we went well in dry practice, unfortunately our carb settings did not suit the weather conditions on race day. A rich needle meant that both motors flooded on closed throttle & often took several seconds to clear after each corner. We (well at least me) must have looked like right amateurs racing down the straights, then costing for 10m or so after each corner while we tried to get them firing again. Nathanael managed far better than I did. Unfortunately I had no time to sort this prior to the race as my motor had popped a crank seal at the end of practice & it took me ages to diagnose & fix. I completely missed qualifying & only got it back together just before the race. Roll on the 2011 GP, though by then there may be a grid full of 30 RWHP buckets to compete with!
Looking back over 25 years of bucket racing, in F5 my best national GP result on the RG was 2nd, on the TZR 1st, also 1st on the TZR-Derbi & 1st on the RS-Derbi. In F4 my best national GP result on the RG-TS100 was 4th, on the TZR-MB100 2nd 3x, on the TZR-FXR150 2nd twice. I’m still waiting for that elusive F4 GP win (which is looking increasingly unlikely given that I turn 52 this year).
Moped rider
As a follow-on, I have been contacted by the guy I sold my son’s Metrakit GP50 to. He has moved overseas & wants to sell the bike. A bit of a shame as he never even raced it. But in Googling the bike to see if I could find the old Trademe listing (to save him having to do the research again), I found some postings on this site that questioned the legality of this bike. Even though I don’t own it anymore, I thought I should clear that up. Metrakit make a range of purpose built race bikes. Almost all of them use race modified Derbi or Aprilia motors. However the base model uses a bog standard street 50cc motor, in this case a Derbi. It still has the standard Derbi ignition & tiny 13mm carb. All internal parts are bog standard, only the pipe has been upgraded. So even though the chassis is a dedicated race item, the motor is not. It only makes 10-11 hp & is absolutely legal for buckets in NZ.
In a similar vein, the Yamaha TZR50 I raced a few years back is also a genuine street bike, that comes complete with lights etc etc. Again absolutely legal for F5. Many people confuse it with its sister TZ50, which is the race version of the same bike. There are a few of these in NZ & by the letter of the law they are illegal because they are a purpose built racer. But in my view it is a somewhat grey area in that the street TZR & race TZ are almost identical. I have the parts books for both bikes & most parts, & even most motor parts are identical. The pipe, carb & ignition are different, but almost all internal motor parts are identical – nothing that would give an unfair advantage. You’d have to be pretty observant to spot the difference & you’d have to have pretty rigid views to exclude the TZ from racing.
Unknown Disorder
To be honest with the number of F5 bikes running at the moment I'd say you'd have to be insane to exclude anything that fell into a grey area.
On a more positive note I know of a couple of F5 builds going on at the moment so maybe there will some sort of class resurgence.
Also, if anyone knows of an RG50 for a resonable price let me know, I got hooked after riding Cullys.
Was worth a crack
Have you based your porting changes on time area or is it more about duration and angles?
No8 Wire Extraordinaire
Good post Dave, good to hear your point of view here. Forums can get somewhat distorted.
As a side note; what markets have had Derbis released as 70s or 80s? Do you mean released by Derbi as a new road bike? Or you mean the kit parts have been released?
Dave was a great help to me back in the late 80s with a pipe design for my MB50 which helped match & then some the brand new RG50s that had appeared on the scene. There had been some muttering at the time that the RGs were like cheating as they cost $1700 new & there was talk that buckets should be 7+ years old. As it turned out they got cheap quickly (I didn't buy mine until it reached $400) & they single handedly (if that's even a real word) saved the F5 class. Sounds a bit familiar.
If Dave added the list of Auckland race wins/club champs/2hrs to his resume it would take the next few pages.
Don't you look at my accountant.
He's the only one I've got.
Hardcore Biker
Thanks Dave. I hope to give my Rg50 to Georgie, when i get it sorted and build a F4 bike. I have been talking to Wobbly about F5 motors and which one to use. He mentioned the Derby , but making a 100cc motor from one. Looks like it could be harder to get 30hp from one than we first thought
Hardcore Biker
I have Dave Mullins old Honda 50 on loan for Georgia to try. Its very standard, but if i can get it running you are welcome to ride it until she decides what she is going to ride
If this rain stops !!!!!!!!
Forum whore
Dave Mullins is a name I haven't heard for years and he is a top bloke!!!
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