OzVMX Forum
Clubroom => Tech Talk => Topic started by: ChrisACT on February 05, 2013, 09:56:49 pm
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Hi guys,
I have put a DT100D engine in a DT175a frame, and I now need a rear wheel which will fit the DT175A swingarm but has the same sprocket offset as the DT100D (70mm from the centre of the hub to the centre of the sprocket). The DT175A rear wheel puts the sprocket way too far wide of the mark.
I'm thinking that a 70's YZ125 or DT125 wheel might be about right. I'm happy to lose the DT100D cush drive anyway. A 12mm axle would be good as it saves me having to mod the swingarm.
Anyone know what the sprocket offset is on those bikes?
Thanks,
Chris
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why not space the 100 motors countershaft spocket to match the 175 rear wheel ???could be easier then trying to make the wheel work with the 100 motor ;)
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I'm not really sure how I could do that. The countershaft doesn't have enough length to space the sprocket 6mm further out.
As it is, if I go with the DT175 rear wheel, I'll have to run a 428 chain instead of the 420 and the extra thickness of the front sprocket will take up any of the shaft that is left.
So, unless an offset front sprocket exists which would fit the counter shaft, it'll probably have to happen at the rear wheel.
But thanks for your reply.
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ok got you with the lack of countershaft length so why not machine the desired amount off the hub or cush drive hub where the spocket bolts on to get everything to line up again
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Not totally sure but off the top of my head the DT100 cush drive should fit into the DT175 rear wheel.
Or,
The MX/YZ125A/B rear wheel should be a close fit/offset.
Im currently putting a DT100 donk into a TY175 frame and the MX/YZa wheel is a good fit/offset etc
I thought the rear axle was 15mm not 12...
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Hi, might be thinking back to front, but would a 'dished' AG100 type front sprocket get it close to working [ie' in line with rear], or if you were real desperate [i'd do it haha], machine the teeth off the dished front & weld another sprocket outside that to step it out even further after machining the middle out of it so as to get at the nut. Agy's are 428 as are DT175 of course but if you wanted a 420 & found a rear i'm sure you could organise a front 420 to weld on too. [I'd stick with 428] Good luck. ps, like i said, hope i'm thinking right & not got story back to front.
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Chris, the hub centre to sprocket distance did differ across early YZ125 hubs. Nathan S knows all the details, and may (may) be able to help you with a hub with the right amount of offset.
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Chris, you should ring me.
Super shortened version:
YZ125A/C have a dished rear sprocket.
YZ125X has a flat sprocket and more meat on the hub to put the sprocket in the same spot as an A/C.
DT175 mono shock has even more meat, to move the sprocket further to the left.
0400023847.
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I'm sure you've seen these but here's a pic of a worn out one. Is AG100 but would have to be the same spline as a DT100. Have an XR200 type motor [made up from bucket racing leftovers] which is in a PE250 frame & had to do the sprocket "step out" thing to get it somewhere near lining up with rear. Been ok for 10+ years.(http://i1276.photobucket.com/albums/y476/gasgirlings/PIC_0840_zps42eb8072.jpg)
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Hi guys,
Thanks for all your comments.
The AG100 sprocket might fit the bill if I can get them in a 15 or 16 tooth.
Matt, the part of the DT175 hub on which the sprocket mounts is 10mm thick. Machining 6mm off that wouldn't leave much left of it for the sprocket to hang onto. This is an odd project involving methanol and much higher speeds than the old DT's were ever designed for. I'd hate to lose a rear sprocket along the way.
Vandy, you're absolutely correct. The DT175A has a 15mm rear axle. Oops. But the DT100D cush drive will definitely not fit the DT175A rear wheel. Although the DT100D did have a totally different frame and swingarm compared to the DT100A - C so potentially the rear wheel and hub was also different.
Nathan, what I need if I'm going to change the rear wheel, is less meat under the rear sprocket. YZ125A might do it. I'll call you tomorrow.
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Where have you been Chris, uni finished and back into the shed? ;D
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LOZZA!!
Yeah, mate. Uni is all done and I'm gainfully employed again. I'm writing software for mainframes these days. It's very nice to have an income after three years in the financial wilderness. I can get back to building silly motorcycles. I have plans to visit Lake Gairdner next year (which is what this thread is all about). It could be hilarious. ;)
You still up Newcastle way?
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A friend is off to the salt very soon actualy everyone is pumped after 2 yrs of being washed out. Yep still in Newcastle. Good to hear you have some play money.
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Yeah the poor buggers have been pretty unhappy with the weather out there. But still, this year should be a big event. Obviously, I won't be ready by then so next year is the go. Lots of prep to do on the bike, dyno work etc. and I have to get the scrutineers to look it over before I set off. Running methanol requires a fuel shutoff and they want a bombproof chain guard etc. Lots of rules. Luckily the chief scrutineer for bikes lives near Canberra.
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What class?
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M/F 100cc
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what's the record in that class?
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In Australia it's open. Internationally, the fastest record I've found for this class is about 102mph at Bonneville. There's no "world record" as such.
A record would be nice and is obviously a goal but ultimately I just want to see how fast we can go with it.
The M/F 100cc class is for naked bikes, so no fairings on this one. Can't even have aero aids on my leathers or helmet. I reckon at least 30HP is required to hit 100mph.
What could possibly go wrong? ;)
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Hell, now i'm sitting up & taking notice. Good luck with the project in taking the speed record.
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Are you allowed water cooling? Aero will play a big part in top speed even down to how you have your feet on the pegs. What engine?
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The engine started life as a DT100D engine. It has had a fair bit of work done to the barrel (it was my old Superlight race engine) but I'm going to do a lot more to it. Planning to spin it to 12,000RPM which it'll do all day.
MOTA reckons that 30HP on methanol at 11,250PM is easy peasy.
If I can't get the required HP out of it on straight methanol, we'll start playing with nitromethane. A 10% nitro, 90% methanol mix should produce 40HP at 12,000RPM with the same pipe. The question is, will it become a 100mph grenade?
I can water cool it if I want to but that adds another degree of complexity and stuffing around. If we get the record, the next thing to do will be to streamline it and go with a cooling tank (no radiator to slow me down) and then run it in the special build class.
The record for that class is significantly higher (off the top of my head I think it's about 170mph), :o
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Hmm give me a ring one day or PM your number. Nitro will mean wrecked pistons as you will be WOT for 2-3 miles
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Awwww, but I only wanna use a widdle bit. :'(
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That's what every HP junkie tells me in the beginning ;D
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The plan is to do many runs on straight methanol before we start playing with nitro ... and even then, only if we can't get it to 100mph.
We should have some good data by then of EGT, CHT etc which will hopefully give us some idea of whether or not it'll take any more heat for that duration.
The track we'll do most of our work on is only 3 miles long so the most it'll be WOT for is 2 - 2.5 miles including the run up. Probably only on the redline for less than half a mile. There's no timed area on the short track so it's GPS speed only. Once we get it singing along, we move to the 9 mile track and run it there for a timed run. The timed area is only 400 metres long. So the trick is to peak at the start of the timed section and run it flat out for that 400 metres then shut it down. The data we get on the short track should give us a good idea of when to coast and when to run it hard so I'm not just holding it wide open for miles.
Rear drum brake only plus the surface of the salt itself means stopping quickly isn't an option which is only an issue on the short track.
EDIT: After reading the 2013 rules, it seems I won't be on the long track anyway. I'll be doing record runs on the short track where I'll be timed over 400m leading up to the mile 3 marker. Then I have to turn off before the mile 4 marker.
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After a bit more simulation work, I agree with you Lozza. There won't be any need for nitro. I can get 35HP @11,000RPM on methanol without too much trouble. Will run cooler and there's less chance of making mistakes with the mix. No need to muck about with Hygrometers at the salt then either.
Another mod I'm looking into is a V-Force reed block. Apparently the '93 - '01 YZ85 reed block uses the same bolt mounting pattern as the DT100. The V-Force item for that model should almost bolt straight in (might need a spacer and maybe a little die grinding - a little more crankcase volume might be a good thing anyway). Simulation says another 1HP across most of the curve. Every little bit helps.
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Lozza, what EGT do you reckon I should be shooting for on this baby?
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I don't think you will see 35hp from a 100 you would need to spin to 14-15000 rpm (which is where I would be tuning it for). Would use a CHT and EGT, if the CHT stayed stable at say around 100deg C might be able to get away with 1150-1200F.
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I know guys who were allegedly getting 32HP on e85 in Superlights (Honda H100 engine). I'd believe it too. They were blowing everyone else into the weeds. They were spinning it to 14,000 RPM though and regularly eating small end bearings. The H100 has a longer stroke and smaller bore than the DT100.
I have EGT, CHT and EGO for it. Running a Mychron 4 2T data logger and dash with all the fruit.
I'm also looking into whether or not I can graft a Yamaya KT100J head onto it. The bolt pattern is almost identical (haven't measured one yet) to the DT100 head and it has more cooling fins. And being a dedicated race head, presumably it's up for a bit more torture than the RT100 head I have on it.
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would a KT100 cylinder work too [or be allowed], should be same 52x46.[46.5] used a piston in my bucket once when de-stroking & over boring my TF100 [another cock up of mine but did work ok for a bit, used an Rd200 crank [one side of]. KT100 is piston port of course but [have 'kart sport manawatu' down our road] the modified ones fair scream. Was a bit slow off the mark other day & missed what it was, but something down there sounded "off the planet" for revs & bulk power--possibly a rotary valve 125 Italian motor i had to chase the noise of once. Sorry, that was a lot about nothing wasn't it. ps, KT100 pistons go in very small increments ie 52.25--52.30 etc etc. long ago but think that's right, plus very thin single ring.
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I know guys who were allegedly getting 32HP on e85 in Superlights (Honda H100 engine). I'd believe it too. They were blowing everyone else into the weeds. They were spinning it to 14,000 RPM though and regularly eating small end bearings. The H100 has a longer stroke and smaller bore than the DT100.
I have EGT, CHT and EGO for it. Running a Mychron 4 2T data logger and dash with all the fruit.
I'm also looking into whether or not I can graft a Yamaya KT100J head onto it. The bolt pattern is almost identical (haven't measured one yet) to the DT100 head and it has more cooling fins. And being a dedicated race head, presumably it's up for a bit more torture than the RT100 head I have on it.
Except when all the big HP buckets get put on a proper dyno they all read way way less,e85 isn't allowed in buckets either ;) Last 3-4 years there has been no H100's near the front, and if they are Lindsay McKay's been riding it
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Yes. That H100 went well, didn't it? 8) He used to outrun all but 2 or 3 of the Motolites.
I didn't think e85 was specifically outlawed until it had been available for a year or two. I was considering it as an option.
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Lindsay's bike is a 125 and water cooled running in P5 125. Fuel is as per the GCR's and you can only have 100 RON fuel and e85 is 115 RON. It's a good alternative to methanol, tuning is half way between ULP and methanol.
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I can't say I remember them ever checking fuel at a PCRA meet. Mind you, I was told by the engine builder that they got that HP out of it on a dyno on e85. In no way am I accusing anyone of cheating in a race.
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Marcus de Caux has this takes 2 min to test and use of e85 was uncovered.
http://www.digatronfueltester.com/
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pcra have check fuels at a meet ask the phantom next time you see him.
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;D
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I think Marcus must have acquired the fuel tester after I stopped racing with them.
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A friend is off to the salt very soon actualy everyone is pumped after 2 yrs of being washed out.
for those interested
Todays News 8)
http://www.abc.net.au/news/2013-02-19/racers-make-speed-assault-on-salt/4526670
home base ;D
http://www.dlra.org.au/forum/index.php
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http://www.apriliaforum.com/forums/showthread.php?247737-RS-250-Land-Speed-bike
some reading for you Chris ;D
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http://www.apriliaforum.com/forums/showthread.php?247737-RS-250-Land-Speed-bike
some reading for you Chris ;D
Thanks, Lozza. I've been following his progress on the DLRA forum. There are some great machines being put together. Mine is a bit of a laugh by comparison. But it's a start.