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Post by triffid on Sept 8, 2015 11:17:53 GMT
Hi Steve, might just be me but in the picture the fan seems to fit right inside the new bit of cowling and I can;t see where the air will exit to get pushed around the barrell?
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Post by tzsteve on Sept 8, 2015 15:26:52 GMT
it`s an illusion,
there is plenty of room round the side of the fan as the coweling tapers and the fan don`t. also the fan is about 40 ot 50mm smaller than a standard one at a guess
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Post by tzsteve on Sept 8, 2015 19:35:15 GMT
someone else also mentioned to me that the cowel looked a bit restrictive. never ask and never post if you are not open to sugestions and ideas( that`s what forums are about). heres two pics from the back of the cowel with the fan in position, i have marked the edge of the tapered portion with a little white marker for clarity. i`m still convinced that there is enough space for air flow. opinions welcome as things can still be modified.
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Post by tzsteve on Sept 9, 2015 9:20:45 GMT
as an engineer i like numbers so i did a couple of simple sums and ended up with these figures about the fan clearance and areas etc. the dark blue is the fan and the light blue is the cowel. i think i have enough clearance around and behind the fan.
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Post by triffid on Sept 9, 2015 11:32:15 GMT
Ah, that's much clearer, didn't think you would have made such a mistake, good to see the detail in your workings though
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Post by tzsteve on Sept 16, 2015 14:49:38 GMT
DRT con rod kit has been ordered and should arive in the next day or two. specs for the kit are 105mm polished rod, silver plated big end bearing and £55-ish delivered. the theory is that plated big ends are less prone to stress (i feel that if a maker is going to go to the trouble of plating a bearing they are more likely to get a good bearing to start with) also a longer rod can raise the red line of the big end by a few hundred rpm. a longer rod does reduce the port timings by a small amount but as the the angle of the rod at mid stroke is reduced in theory the engine is more efficiant (thats what i was told at big word school). the inlet port on the case has already been opened out leaving about 1.5mm sealing on the pad. with a standard ETS crank that gives an inlet that opens at 110 BTDC closing at 63 ATDC. total inlet timing of 173 Deg. i have found that an inlet in the region of 195 Deg is ample for a fast road scoot, i know some people often go as big as 205, but i find that 200 or more can make for a very peaky engine. OK for racing. i did a couple of simple calcs and it works out that each mm that the inlet port is extended gives about an aditional 1.2 Deg of inlet. if i take 15mm of the crank i get a timing of 193 Deg, 19mm would give 198 Deg so after splitting the crank i marked it at 15mm with a bit of tape. a bit of time on the bench grinder and i end up with this then sit on the bench in the garden with plenty of coffee, a Rotozip fitted with a 12mm diameter stone, followed by a small round file and some emery cloth. i ended up with this the inlet was opened up by a total of 17mm by the time i had done all the grinding and removing of the forging marks and the flash (rough edge left over from the forging process) inlet timing is now about 195-196 Deg next job is to press the crank back together and alter the end of the taper for my flywheel bolt. if i was not replacing the big end or rod i would not split a crank just to cut the inlet, i would do the inlet with a diegrinder / rotozip and plenty of tape as every time the crank is split the hole for the big end gets a tiny bit bigger meaning that an oversize pin or welding could be required. oversize pins can be very difficult to find as the normal thing is for the makers to only supply standard size pins. if you are lucky your local crank man may take the time to go through a number of rod kits and dig out just the right pin. (normaly they just fit the first kit they get hold of and tell you "thats right mate" "it`s one of the best i`v done").
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Post by unclechufty on Sept 16, 2015 15:54:01 GMT
Buddy, as always, impressed with your engineering skills, finesse and knowledge. There's always something to learn from one of your posts.
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Post by tzsteve on Sept 16, 2015 16:14:13 GMT
chufty you are easily fooled, i know nout that you cant find in a book. but thanks
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Post by potatopl on Sept 16, 2015 21:09:19 GMT
Nice. What about balancing the crank?
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Post by tzsteve on Sept 16, 2015 21:32:22 GMT
i normaly drill a hole of some size (about 10mm dia) in the web at a later stage. i will post pics later. i dont try to work out the exact balance but rather just take a bit out of the web to try to help a little. balancing a crank assumes that the preasure on the piston is constant i don`t think it is.
in theory the crank shold be balanced to about 65% of the weight of the piston, rod, and small end. i rather think crank balancing on twostrokes can be a bit hit and miss especialy once you start swapping pistons and rods. i think it`s more importent to get the flywheel well balanced especialy if it`s a big heavy sod.
just to give you a headache i will dig out some of the maths and post it here
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Post by henri on Sept 17, 2015 6:43:23 GMT
quick maths thing , standard balance for a single is 60% , you can balance to 100% but engine will still vibrate/jog , just up n down instead off back to front , an thats my clever fact for the day ,back to being the village idiot now an lookin n learning from this thread . H
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Post by tzsteve on Sept 17, 2015 14:46:56 GMT
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Post by tzsteve on Sept 18, 2015 15:21:18 GMT
one hell of a bad day, the DRT rod kit arived.
the pin was smaller than the pin already fitted by 0.015mm and of course the bigend eye is a good fit with the pin supplied and did not fit on the pin that i already have. so out with some french poilishers rubbing powder extra fine (grade 000) its about as fine as ciggy ash i used an old pin with an old bearing and put the new rod on this lot and used the rubbing powder and a bit of oil, then spent 40-50 minutes spinning the rod on the pin and testing the fit on my old unused pin with the new unused bearing every couple of minutes.
eventualy the fit of the new rod and the old unused pin i already had felt right. so now it was time to press it all back together.
BINGO! next problem, a standard rod has a small chamfer on one side of the bigend eye where it sits in a recess in the crank web. the new rod did not have this chamfer so more time spent on the lathe getting this sorted.
so tomorrow i should get the crank back together, then hope that my mate who`s a better welder than me will weld the bigend in for me. no pics with this post as i was running out of time and had to get to my job.
the really annoying thing is that this is advertised as fitting vespa 90/125`s etc i have a hunch it`s probably for a T5. the porblem with the size of the bigend pin is typical of scooters in general i.e. most dealers don`t give a fig about what they sell
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Post by henri on Sept 18, 2015 20:52:17 GMT
you need to take satisfaction in knowing " they wouldnt of sold it to ya if they didnt have confidence you could fettle to fit" , its a personal triumph over the vicissitudes of scooter life , we have faith in ya steve , deep breath n carry on , an for the doubters , well i'm dwunk an the censors acting on this forum wont let me express my pain , you get my drift , H
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Post by tzsteve on Sept 18, 2015 21:40:13 GMT
thanks H, your very generous. it`s just annoying that NOTHING EVER FITS! as prommised
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Post by vader19 on Sept 18, 2015 22:18:44 GMT
the really annoying thing is that this is advertised as fitting vespa 90/125`s etc i have a hunch it`s probably for a T5..... most dealers don`t give a fig about what they sell. Nothing surprises me anymore when it comes to the descriptions of parts from the vendors and what the reality actually is.. it's amazing how few things advertised for bike "X" actually fit bike "X" w/o modification or shipping back for a different part.. and how few parts (especially performance parts) are truly "plug and play"... Sorry you're getting stuck w/ this unneeded work Steve, but it sounds like you've got it handled of course.
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Post by tzsteve on Sept 19, 2015 14:35:11 GMT
just a few pics of the fun and games i checked the rod to make sure it was straight easy test. no it was not straight. the difference was 0.1mm when i compared the measurements from one side to the other fixed that with a number 2 copper mallet in a couple of seconds by holding the rod in the palm of my hand and giving it a few taps . the pic of the two rods shows the difference in the bigend eyes. this rod is not made for a smallie but as far as i know the sizes are the same as a T5. balancing the crank? this is typical of what i do if i split and cut a crank. i do not have a sientific aproach to this, i just drill a couple of holes and hope for the best. if i cut the crank but don`t split it i drill a couple of holes into the edge of the web rather than the sides again no scientific aproach it`s just what i do. the pic of the web balanced on a welding rod shows that the center of gravity for that web is still pretty close to the center line of the web. this is just good luck then check the crank for runout, it seems ok. i got the total runout to 0.0005inch after a few wallops with a number 4 copper mallet. as i have reused the original pin it is not a very tight fit in the crank so welding will be required this was obvious and showed up by the ease with which the crank could be knocked round when truing it up. i guess that if it was for a 5BHP scoot the fit would be ok but i dont think it would take long to twist out of true on anything with much more than that. my buddy the really good welder has a decent crank checking jig so i hope to check it on that aswell. the choice now is to weld the bigend with mig or tig. both have their own advantages. mig is cheap and quick but needs grinding back afterwards, tig looks nice costs more and puts more heat into the pin. the next thing to look at is gearing. 5 transfer quatrini m1 single exhaust port big inlet 34mm amal franz pipe any tips gents
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Post by henri on Sept 19, 2015 14:44:26 GMT
or instead of welding pin the crank , 1-2mm hole down the join line an hammer in with loctite a old needle bearing which is a tight fit to the size hole drilled . use to do that on cranks i knew i'd need apart again someday , interesting info on rod lengths being same as t5's , mate seized his tother day so was idly offering up the barrel to a set of cases n wondering "what if" ,would need serious welding n decking to get ports covered n studs spaced different .would be handy not to have to change rod on crank to do it ,will have to compare strokes on them . H
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Post by tzsteve on Sept 19, 2015 15:10:26 GMT
` i doubt that a primmie crank would be strong enough for pinning the big end, but it was standard pratice on a lot of the kawasaki tripples
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Post by henri on Sept 19, 2015 16:37:00 GMT
thats the sort of lump i use to do it on ,an big brit singles/twins , H
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