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Losh's 1976 Yamaha RD 400

Discussion in 'Miscellaneous' started by losh1971, May 28, 2018.

  1. losh1971

    losh1971 Well-Known Member

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    [​IMG][​IMG] bike.gif bike.gif bike.gif bike.jpg

    Bit about my bike. It has a blueprinted engine with machined down crank making it very smooth compared to stock and getting decent amount of weight off the normally quite heavy 400 crank. It has Wiseco pistons and TZ350 race big ends. It has an undercut gearbox and thicker clutch with CB750 clutch springs as it was slipping due to the increase in HP. Match ported with 34mm flatslide Mikuni's. A set of chambers made by Neville Lush and tapered headers off a RG350. Ignition is off a KX80 with modified black boxers to suit the RD. Reeds are off a KX 80 also. Reed blocks have been opened up to give plenty of flow and take the larger KX 80 pedals.
    Last time I rode it was at Mallala on a ride day to test out the new front shockers and springs after getting Race Bike Services in Lonsdale SA, to fit emulators. I have stripped probably 25kgs of weight compared to stock. On the front I have RD400 1978 forks and spoke wheels. Front hub is off an early RD350 and the rear a 2.75" rim wheel off a TZ350 that I had the hub machined down to suit the RD gearbox and swing arm. It will rev out to 9.5k and makes decent HP anywhere from 6k -9k , with max at about 8.7/8.8k.
    Hoping I can get it over in Oct this year but I want to get a pair of RD 250 heads reshaped to suit the 400 while at the same time get a better shaped than the old stock 400 heads I'm currently running with, I'm thinking I will get gains of around 5hp with the new heads and the power curve should hopefully then have no drop or virtually no drop from low revs right up to max power. Once I do that I will need it dyno tuned again and really need Neville to do that as he is the man and will save me melting a piston. Needs new tyres before I try it out at Symmons and I'm thinking I will go with Dunlop Gp's as I can not get Avons in the size I need in Australia.

    Lunchtime today I spoke with Neville and he has booked me in to get the heads reshaped. When I see him I am going to ask about getting power valves made as that would give me more power in the lower rev range and could help to get me off the line a bit quicker.
     
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  2. losh1971

    losh1971 Well-Known Member

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    So far the bike owes me about $8k, with around $4.5 of that amount spent on the engine and trans. If I get the heads reshaped and the bike dynoed this year as hoped I will be putting close to another $1k into it. I have an old DT 175 air cooled that I plan to sell for around $600 which will get me most of the way to paying for the work on the 400.
     
  3. losh1971

    losh1971 Well-Known Member

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    Bit more about the bike. When I built it we took everything off that could cause drag on the engine. This included removing the speedo drive, kick starter, oil pump. We also replaced the rear sprocket with an alloy one to reduce the amount of weight the engine had to turn over.
     
  4. lmoengnr

    lmoengnr Well-Known Member

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    A mate and I used to share an RD250LC in C grade Production races at Calder.
     
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  5. EYY

    EYY Well-Known Member

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    Interesting thought about the powervalve - I'd be interested to know how you'd intend to go about it. Means you can go with MUCH more aggressive transfer and exhaust port timing. But basically involves a complete redesign of your cylinders - especially if you want to take full advantage of a powervalve system. How would they be activated? Servo operated or governor operated?

    For your purpose, you'd probably be able to keep it singing pretty well so a powervalve system probably really isn't worth the time and effort overall tbh. Unless of course you're spending a lot of time in the lower rpm range.
     
  6. losh1971

    losh1971 Well-Known Member

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    I don't know a lot about the power valve, only that Neville mentioned he could make them. The main attraction would be getting off the line quicker. I have to ride the clutch at the which is quite normal on 2 stroke race bikes. The other place it would benefit me is coming out of hair pins. At the present I have to be in low gears, like 2nd but still in the power-band or you have trouble when you are racing against modern 750 4 strokes that just pull hard even in low revs. I was in a race with a girl on a 750 modern and on the corners I would catch her but pulling out she always had me at low speed. I eventually learnt to keep it in 2nd and power out soon as I hit half way. But the issue was I would get rear wheel spin which would be ok if you're a really good rider I'm fairly ok, well was. But the really good riders in the same race pull 1.14's at Malalla and I was more an 18-19.
    having said that the reshaped heads will probably improve things in lower range. The really good riders expect to have wheel spin. I remember one bloke on his 750 triple 2 stroke used to wiggle his front wheel to get it to slip just a tad so he could get corner faster but he was an insane rider who won the nationals.
     
    Last edited: May 28, 2018
  7. losh1971

    losh1971 Well-Known Member

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    When I eventually race again I want to have a really competitive bike because some guys on their moderns may not be the best riders but because everything in newer tech they have the edge on you before you get out. I'm pretty ok on the corners and I like to out-brake a lot of guys. Even though I'm on an old bike my front brake has a bigger disc off a 650 Yam of a similar year so I have some pretty decent stopping power.
     
  8. losh1971

    losh1971 Well-Known Member

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    Last time I rode my mate came out with me on his GSXR and he loved it and was surprised how well the old 76, RD 400 could be pushed around. Racing is an addiction though that you keep needing more power because what ever you have is never enough.... I imagine it is the same on dragway you always want more HP....
     
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  9. losh1971

    losh1971 Well-Known Member

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    I will ask Neville what he thinks and a rough idea on cost. If it's 2k then the answer will be no. But if the price is right it could mean I could increase the porting on the exhaust side as I wouldn't always have to be in the power-band. There are a few factors that mean I am getting to the stage where I am going to have reliability issues if I try and squeeze too much more out of it, due to heat. As it is I have to watch I don't increase the compression too much or it could seize. If they allowed methanol in Period 5 (assume they still do not) it would be a no brainer I could achieve 65hp or even more and not be concerned with over heating.

    In terms of activation I'd have to ask Neville as I don't run a battery so not sure how he would trigger it. When you say port timing what do you mean, increase the size?? Or do you mean enlarging the port on the bottom only and leaving the top?
     
  10. EYY

    EYY Well-Known Member

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    Port timing is the whole picture - raising the exhaust port decreases low end but increases top end and also decreases dynamic compression. Widening the port will have a pronounced effect throughout the midrange and bottom end all else remaining equal. You can play with base gasket thickness to get an idea of what works - but you need to be careful of squish and compression ratio.

    Do you have an exhaust bridge? Sometimes a bridge is required to support the piston on the exhaust side if you’re widening the port considerably, but that requires resleeving.

    Heat will always be an issue on the exhaust side on a 2 stroke at sustained high rpm - desert riding for example. On a track I’d say you’d be fine as long as it isn’t held wide open for minutes at a time. Only takes a few seconds of closed throttle to draw enough cool air past the exhaust side to stop things from melting.

    2 strokes are inherently forced induction by design. That’s why crankcase volume, reed valves, port timing and pipe choice is so critical.

    As a matter of interest, what oil do you run?
     
  11. losh1971

    losh1971 Well-Known Member

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    Yeah Neville has to measure the squish and calculate the compression difference prior to reshaping and fitting the 250 heads. He want's to keep the compression similar to what it is now so as to reduce any likelihood of melting a piston. I currently have paper base gaskets 2 to help with getting the barrel heights right. Ideally it would have a third one but that runs the risk of it sucking in the middle one and it leaning out. I really need to one day get a pair of copper gaskets made and he may tell me I need to in Oct. That would mean the bike may not get dynoed though because it will take a few days to make them in Melb and I'm only in SA for 7-8 days. Heat is really only an issue if you running petrol or Av Gas, methanol runs way cooler, just never used to be allowed in Period 5, mainly I think because the TZ 750s make enough power now without going spastic and running meth.

    As for oil I use Rockoil synthetic race oil at 33/1.
     
  12. losh1971

    losh1971 Well-Known Member

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    Also it doesn't have a bridge and Neville never mentioned getting one. He hasn't gone spastic on the exhaust porting mainly because as you know it becomes harder to ride if you have nothing in the mid but mental power up top. When he built the motor I was given the option of going crazy with porting but then it becomes like a TZ and unless you're constantly sitting on 8k or above you don't have the mid range torque, like my 400 has. Some of the guys that race TZ 350s in Period 4 & 5 have two bikes something like an RD 350 which is fair bit lower power but just not as hard work when your in a race. If they want to win they pull out the TZ, depending who else is on the track and what the other really trick guys are riding.
     
  13. Deuce

    Deuce Super Stock

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    Loving this 2 stroke education lesson.
    Would love a vid or sound clip of it winding out or passing by, or pulling out of a corner.
    Keep up the good work mate.
     
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  14. losh1971

    losh1971 Well-Known Member

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    Booked my bike engine in for the first the first week of Oct. I have a set of 250 heads that Neville Lush is going to reshape the dishes to make the RD 400 go even better. I'd love to have it dynode while he is at it but it's gonna come down to finance. Heads alone will be 500 bucks, dyno would be another 250 or thereabouts. If I don't dyno tune it I'd have to wait and take it back to Neville to have it dynode before I bring it over to Tas. I have almost decided to flog the DT 175 air-cooled, which is how I plan to finance the upgrades on the RD. Kind of want to keep it because it is a great little trail bike. But I've ridden it no more than five times in four years for no more than 15mins at a time. I just haven't had time with building the house and also spending plenty of hours working on the ute. At least the house is now finished except for fences, and doors on the linen press & pantry. I want to keep the DT on one hand, because I doubt I will ever get another dirt-bike if I sell it. But then again it just sits in the shed not being used. Just can't decide.... I need the boss to take another two weeks leave before I head to SA for two weeks in Oct, if that happens I won't need to sell anything because I will get two weeks full-time hours.
     
  15. afstruct

    afstruct Well-Known Member

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    Once it's gone you'll suddenly get opportunities to use it.
    I only used the Suzuki about the same in the last few years . Am loving using it again ( or after these few weeks not!!! , will again hopefully this coming week ).
    Slip a flu virus in his coffee, ha ha ha .
     
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  16. vc commodore

    vc commodore Well-Known Member

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    There is a place in Burton that makes copper gaskets....Can't remember the name of the place, but should be able to find it without too much drama if required
     
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  17. losh1971

    losh1971 Well-Known Member

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    Burton Adelaide? I wonder if Neville my mech knows about them. Copper would be ideal to set the barrell height to where it is perfect.
     
  18. vc commodore

    vc commodore Well-Known Member

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    Yep....Waterloo Corner Road past Burton Road intersection, heading towards Port Wakefield Road....Just can't remember the name nor the address of the place....But he is located in a group of sheds down that way
     
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  19. losh1971

    losh1971 Well-Known Member

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    Well things are pretty tight with all the coin needed to finish the house and then the ute, AKA money pit.... But some fortune this week. I get back from leave today and the boss goes home soon after 9am. This means I get to work until 3.30pm then I go up to my boss' boss to ask about doing a new time sheet and he says my boss is off sick until Thursday. That means an extra 9.5hrs. Answer to prayer that one, means I'm on track to putting some money aside for my RD as well as getting trans cooler fitted to the ute before I leave. :):)
     
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  20. afstruct

    afstruct Well-Known Member

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    Nice to know that little bit helps.
    Well his few days of misery is your good fortune.
    Not that I believe I predicted anything (it's that time of year) , I'd say it's time you had a good run with the ute. Unfortunately I don't believe I can predict anything , it I could surly I would have predicted a few reasonable lotto wins by now.
     
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