paul8899 Posted July 27, 2010 Report Share Posted July 27, 2010 I'm now at a stage where I am going to have to put my hand in my pocket and start rebuilding the engine on my ypvs 350. First things first, the barrels are on 2.5mm os so I will need to get them relined or replaced, I have seen that pj motorcycles do relining, has anyone had this done or used this company ? While I have the engine stripped down I thought I'd have a little play with the needle files . How easy is it to get the ypvs engine up to 60-65 bhp ? Is it wise to have a go at doing some porting myself or should I get a professional to do it ? Is it worth smoothing out the crankcases where they meet the barrels ? There is about a 2mm mismatch between them ( crankcases are smaller ) Any advice or recommendations welcome Ta Link to comment Share on other sites More sharing options...
GREENGOATCHOKER Posted July 27, 2010 Report Share Posted July 27, 2010 instead of getting them relined how about going up to 375cc . i know stanstephens and others used to offer this . not much to be had top end but gain a little midrange . raising the exhaust port about 1mm will give you a bit more peak and a lot of people knife edge the inlets and transfers . a friend of mine has a pv has a pretty wild pv kicking out 75bhp on what i suspect is a fairly generous dyno and the crank cases have been very opened up and smoothed around the transfers . there are a number of forums that list or people will provide you with maps for what to increase and by how much . probably some useful info here http://www.2strokeworld.com/forum/index.php?topic=3.15 if not a few simple searches will find them . to get real power from a pv means blending the pv's themselves , mucking around with compression and squish , carburation and timing . you shouldn't have any real trouble finding 60bhp but anthing much over 65 starts to cost . as for doing it yourself i guess it depends what you have more of time or money . bare in mind that its much easier to file metal off than put it back if you fuck up Link to comment Share on other sites More sharing options...
johnlc Posted July 28, 2010 Report Share Posted July 28, 2010 instead of getting them relined how about going up to 375cc . i know stanstephens and others used to offer this . not much to be had top end but gain a little midrange . raising the exhaust port about 1mm will give you a bit more peak and a lot of people knife edge the inlets and transfers . a friend of mine has a pv has a pretty wild pv kicking out 75bhp on what i suspect is a fairly generous dyno and the crank cases have been very opened up and smoothed around the transfers . there are a number of forums that list or people will provide you with maps for what to increase and by how much . probably some useful info here http://www.2strokeworld.com/forum/index.php?topic=3.15 if not a few simple searches will find them . to get real power from a pv means blending the pv's themselves , mucking around with compression and squish , carburation and timing . you shouldn't have any real trouble finding 60bhp but anthing much over 65 starts to cost . as for doing it yourself i guess it depends what you have more of time or money . bare in mind that its much easier to file metal off than put it back if you fuck up Personally i would send them to Fahron engineering ,one of the best tuners on the go in my opinion and he also does resleeving ,he could make you a really special motor especially when the liners have been taken out ,allows better access for tuning Link to comment Share on other sites More sharing options...
wazrs257 Posted July 28, 2010 Report Share Posted July 28, 2010 +1 for Fahron. You can get extra power by tuning it yourself, but its very easy to gain a few BHP at the top end at the expense of all your low down & mid-range power. Proffesional tuners have already made their mistakes, and you will end up with much more tractable engine as a result. Most land fill sites are full of home bodged 2-stroke barrels! Your main expense is going to be rebuilding your engine, ruining it with a crap home tune is just false economy IMHO. Link to comment Share on other sites More sharing options...
paul8899 Posted July 28, 2010 Author Report Share Posted July 28, 2010 +1 for Fahron. You can get extra power by tuning it yourself, but its very easy to gain a few BHP at the top end at the expense of all your low down & mid-range power. Proffesional tuners have already made their mistakes, and you will end up with much more tractable engine as a result. Most land fill sites are full of home bodged 2-stroke barrels! Your main expense is going to be rebuilding your engine, ruining it with a crap home tune is just false economy IMHO. thats what I wsa thinking, don't want to finish building my bike up only to kill the engine . Is there a web site for fahron ? Link to comment Share on other sites More sharing options...
cagimaha Posted July 28, 2010 Report Share Posted July 28, 2010 Your main expense is going to be rebuilding your engine, ruining it with a crap home tune is just false economy IMHO. Oi! I resemble that remark IMHO it all depends on how far you want to take it. Increasing the compression (either by removing the head gasket/skimming the head or thinning the head gasket and skimming) will provide an increase in power with a negligible drop in reliability. If don't mind running on super unleaded then you can reduce the squish to 0.9mm safely but make sure you run some cooler plugs and be careful with how much static ignition advance you're running. This will never be as cheap as actually reprofiling the head but it's a damn sight cheaper! Opening out the intake tracts to allow fitment of CR250 reed blocks and big carbs is manageable at home as well and will not reduce reliability. Polishing the exhaust ports and matching the exhaust valve profile to the exhaust port is also possible to do with a dremmel type tool with a flexible extension. Also as has been mentioned raising the exhaust port and widening the intake port and knife edging the bridge are also achievable without specialist tools. The main stumbling block of the home tuner is being unable to alter the transfer ports without access to a 90 degree grinding tool. This means that if you go crazy on the intake and exhaust ports but leave the transfers you will end up with an unrideable on off switch. If you go easy you can make a fairly big difference. PB did some articles about what some of the proddy boys did to their 250 and 350 LC's back in the day and I think they managed something like a 12% increase in peak power with little detriment to mid-range or reliability. I say as long as you're careful and you plan out what you're going to do then go for it. There used to be loads of port maps and diagrams on the yamaha-rd.com forum but that had a collapse and has never really recovered. There is still plenty of info out there on the net though. HTH, Ben. Link to comment Share on other sites More sharing options...
paul8899 Posted July 28, 2010 Author Report Share Posted July 28, 2010 when you say reprofiling the head, do you mean altering the shape of the combustion chamber or just getting the squish right ? If you mean altering, do you know what shape to make it ? Thanks Paul Link to comment Share on other sites More sharing options...
wazrs257 Posted July 28, 2010 Report Share Posted July 28, 2010 Oi! I resemble that remark Your not the only one! 250LC. Re-profiled head. Barrels skimmed. No head gasket, o-ring grooves machined in head, then head lapped into barrels. 275cc overbore. Piston crowns machined to match head & equalise squish. 1mm spacers under barrels. Exhaust ports raised. 0.028" squish clearance measured at 4 points around the piston. Had to run it on octain booster! It showed just under 40bhp on Steve Burns mobile dyno then blew its guts out at round Donnington! Link to comment Share on other sites More sharing options...
cagimaha Posted July 28, 2010 Report Share Posted July 28, 2010 Yeah I'm currently doing something equally stupid with a 350LC based lump. Went overboard on the ports then cos I can't do much with the transfers I've bodged it by skimming the barrels then using spacers under them to jack them up to bring the transfer timing somewhere near. Copper head gasket, 0.7mm squish and still running standard ignition so lots of silkolene pro-boost! When it holds together for more than 20 secs its awesome. So are the blow ups though! Sorry for the thread drift Paul, by reprofiling I meant changing the width and angle of the squish band so that the fuel air mix is concentrated as best as possible. It allows you to run more ignition advance and compression without getting pre-ignition and detonation and all the nastiness that comes with it. You can get a similar effect by reducing the squish to <1mm but for the full effect you need to reprofile. If you want to DIY it then have a look at any two stroke tuning books by one of the Gordons (Gordon Blair or Gordon Jennings). Gordon Blair also has created some software to aid tuning both the porting and expansion chambers of two strokes. It gets a bit physics involved if you're not used to it but both of them explain the concepts even if you don't bother with all the maths. If you want to get someone else to do it then I would look up either Harry Barlow (used to have the worlds fastest RD400 dragbike IIRC) or Mick Abbey, I think they are both still in business. Abbey can be a bit hard to get in touch with, he's pretty old school but his work is top notch. Once you do manage to get hold of him on the phone though he will quite happily talk for hours about tuning and will go out of his way to help you do bits for yourself. He managed to ressurect some barrels of mine that had had a shit home tune courtesy of a previous owner. They were ballistic when I got them back from him. He also does one off hydroformed pipes as well I think... Hope this helps, Ben Link to comment Share on other sites More sharing options...
paul8899 Posted July 28, 2010 Author Report Share Posted July 28, 2010 I'll have to give mick abbey a call, I don't want anything too mental ( expensive I wonder if the exhausts start out as flat sheet ? Link to comment Share on other sites More sharing options...
wazrs257 Posted July 29, 2010 Report Share Posted July 29, 2010 Fahron Engineering 0115 963 4123 (Based in Notts) Re-profiling the head also makes sure that the squish clearance is constant around the squish band. If the clearance is not consistant, hot spots can occur which can lead to detonation. All expansion chambers start out as flat sheet, its just the forming process (hydro-forming or individual cones) that differs. Hydro-forming gives a smoother internal shape, but it is much harder to get the dimensions correct (unless you really know what you are doing). I personally prefer the looks of a bare cone chamber, with all the individual weld bands! Make sure that your pipes & porting are designed to peak at the same revs. The best tune in the world coupled with the best pipes in the world wont work unless they peak at the same time! I haven't read the books that Ben suggested, but 'Motorcycle tuning, two stroke' by John Robinson is a very interesting read. Link to comment Share on other sites More sharing options...
2T Institue Posted August 5, 2010 Report Share Posted August 5, 2010 All expansion chambers start out as flat sheet, its just the forming process (hydro-forming or individual cones) that differs. Hydro-forming gives a smoother internal shape, but it is much harder to get the dimensions correct (unless you really know what you are doing). I personally prefer the looks of a bare cone chamber, with all the individual weld bands! Make sure that your pipes & porting are designed to peak at the same revs. The best tune in the world coupled with the best pipes in the world wont work unless they peak at the same time! Basicaly but not entirely true, the best pipes in the world on a crap engine will give a good kick, but not vice versa The RZ or YPVS engine will get the biggest kick from an aftermarket ignition/power valve control, there is not that much in the cylinders and a too good pipe will over scavenge the crankcase. Cone pipes are far more dimensionaly accurate, the 'smooth' look of hydroformed pipes is detrimental to performance. Header pipes are the only bit worth hydro forming. Link to comment Share on other sites More sharing options...
Devon Posted August 5, 2010 Report Share Posted August 5, 2010 Mick abbey is the guy that i would reccomend. i used him to tune my rs engine, very cheap adn the quality of the work was excellent, his after sales service is top notch, he kept ringing me for weeks after to check how it was etc. he can be a bit slow to get hold of but thats because hes also running a pub. Link to comment Share on other sites More sharing options...
paul8899 Posted August 7, 2010 Author Report Share Posted August 7, 2010 I got in touch with fahron eng and I'm going to get them to do the engine work , seems quite reasonably priced . I also got in touch with the people who made greengoat's exhausts and they said they would make a set of exhausts with me supplying the material the only downsides are that they are in york and there's a 3 month backlog at least it will give me a bit of time to get it finished ! The RZ or YPVS engine will get the biggest kick from an aftermarket ignition/power valve control Are you talking about a zeeltronic and how easy is it to get working ? Also, does anyone know if v-force reeds are any good ? Link to comment Share on other sites More sharing options...
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