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how to make your d1 go as it should have gone
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Anderzander
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August 29, 2016 - 8:16 am
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Forgot to add - the D3 barrel and D1 cases were an excellent match too.

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stubaker58
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August 29, 2016 - 4:17 pm
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Would I be right in thinking that the work on the ports and ensuring the piston is not blocking them would also apply to the 175 Bantams?

My D10 head already has a squish band and I have a B175 centre plug head which I keep meaning to fit.  Is there anything else that I could attempt using only hand tools?

When I get my D10 Bushman engine together it'll need a new big end so I'll get the crank balanced at the same time and clean up the ports following the rebore that will be needed.  What do you find is the best tool for radiusing the ports?

thanks.

D7/14 hybrid (4 speed with D7 crank etc.) on the road, D10 Bushman awaiting rebuilding.

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cocorico
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August 29, 2016 - 5:54 pm
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The only suggestion I can make that I haven't seen anywhere else on the forum is that you 'index' your spark plug.

i.e. On an angled head you ensure that the open end of the spark gap faces the centre of the combustion chamber, that way your feeble spark at kick speeds has a better chance of igniting the charge. You may need a few spare plug washers to do it.

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ferguson
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August 29, 2016 - 9:00 pm
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i do quite a lot of porting work-mostly on car engines but some m/cycle.

die grinders with assorted carbide bits work well.air powered much more controllable than most electric ones which rev far too high and can chatter/throw a wooblie far too easily.a very safe way of doing it without serious expenditure is using an electric drill-but not with carbide bits.instead get a bit of approx 1/4 round bar .cut a slot down middle of one end with a hacksaw[1/2 inch plenty] and use the fibre backed flexible emery paper-as used on metal sanding belt sanders etc.2" long strip and just slot it in the bar and wrap rest round bar[facing  'correct' way] pop tother end in drill and off you go.slow and steady but effective.use smaller/larger diam rods and different lengths as required for whatever the job asks for.pop's yoshimura used that method for all the tuning work he did back in the 70's/80's on the likes of the 812 honda.if grinding cast iron carbide burrs run nice and clean-but in alloy they clog terribly .best way round it is keep touching spinning carbide with a candle.stops alloy sticking so badly.oil works but much messier and gets thrown all over the place.

on a different note-i rebuilt a flatpacked bushman for a bloke a few years ago and still had a box of leftovers-included in the pile was a bare d1 carb body so decided to drill it out to see just how far i could take it.the answer is 18mm and the slide still functional.any more and it would start rattling.much to my surprize the inlet side and outlet side didn't quite match up[so i suppose as good a finish as the rest of the bantam!] but with careful drilling they now do.only problems i could see is that the bike might now have a tickover as hole under slide slightly bigger-and you will definitely need to take some off top of slide.in due course i will put it on my bike and see if an improvement and see how the main jet copes.-i will need to slightly taper in the inlet stub on the head to let it breath as well as it can.

ferguson

nearly forgot-yes d7etc  ports respond the same way-just love been tidied up and crisp up the performance.

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ferguson
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August 30, 2016 - 11:54 am
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as an added note on drilling out the carb-used nothing high tech to do it.just a good drill bit and a good pillar drill.hardest bit[as usual ]is clamping the carb true and straight.when drilling alloy it has quite a tendency to try and grab and turn with the drill bit so lots of lubrication and done very slowly.if i'd played safe and drilled it at 17mm then would have increased potential fuel/airflow by a staggering 7.4%.done at 18mm it has a potential fuel/airflow improvement of 12.5%-which in terms of engine tuning is just a huge amount.total time taken 30 minutes-most of which spent sorting clamping of carb body.actual cost -nil -cos already had range of drill bits to cover both sizes

ferguson

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Anderzander
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August 30, 2016 - 8:47 pm
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Topically - I've just got another D1 head, both 55mm stud centres, both obviously measuring 52mm bore size.  However the raised machineed section on the bottom of the head (that the combustion chamber sits in) are quite substantially different heights.

one you could only machine less than a couple of mm off before reaching the limit - perhaps 1.5mm ?   The other I think you could cut it back about 3mm before reaching its limit.  Putting a straight edge across the stud centres and measuring the depth of the chamber though produced the same size.

So they must be just very different castings that give very different opportunities for machining.

I'll use the one with the most metal - skim it and then cut it out to 57mm bore with the extra width giving a broader squish band. I'll also see if I can get that cut off centre so the squish tapers quicker on the plug side.

I'll report back.

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ferguson
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August 31, 2016 - 10:53 am
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laugh now you should realize why i spent my youth measuring bantam bits in the quest for speed.if you find the crank with the longest con rod-match it to the piston that's slightly taller than its peers and find the head with the most meat on and you are onto a winner.we found ,with the right combination, the piston at tdc was level with the barrel top -instead of approx 1mm lower-combine that with a skimmed head that had lotsa meat on it and you have the basics for a bike that will really boogie compared to its peers!

ferguson

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ferguson
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August 31, 2016 - 8:50 pm
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HERSELF decreed i should have a day off today[she watches how much i limp,and knowing i get kinda grumpy when my legs misbehaving,tries to pre-empt the situation by banning me from working].so was pottering around tidying up my workshop and sort of accidentally rebuilt the carb and fitted it to the bikewhistle.pushed it out down the lane and bumped it off cos going downhill.everything as standard with the settings except for the 18mm bore.well fired up no bother but within 50 yards i'd stopped it and was resetting the needle position.lifted it two clicks and bike ran better by miles but definitely needs a bigger main jet as will not run over 3/4 throttle and plug deathly grey by time i'd done 1/2 a mile.unfortunately she heard me return so could not go out again.

so got bored and looked at a couple of other small carbs i had-none will fit the bantam but was more interested in the venturi shape-so decided to put one on the 361 carb.its a subject people write their thesis on and show pages of maths to justify their perfect venturi-so i just copy a wee japanese carb i've got-far easier!on the strangler side i opened it up to 21mm and put a 9mm deep taper on it[jap carb went in 10mm but i didn't have a cutter with right profile so 9mm near enough. on the engine side it has similar but unfortunately the cutter did not have a long enough shank to fit in that far so marked it up with a sharpie and used a carbide cutter and freehanded it with an air die grinder and just finished it by hand with assorted files.made it the same as the strangler side as was on the jap carb.tomorrow HERSELF is at work so testing can begin.

while i was at it i tweaked the main jet.took it out one size with a reamer.the main jet is vastly underrated on a tuned bike and you can tune your jet!-i dont mean by size but by how well it works.amal sizes relate to the flow not the size.a 75 means it will flow 75cc of petrol in one minute[from a set height] unfortunately most dont.they normally reach about 90 to 95% of their flow rate so your max top speed is plainly just unobtanium.if you look at the bottom side of the jet-the bit sitting in the fuel not the needle side- you will see a machined out concave with the jet hole in the middle.that concave shape crucial to the flow rate and amal normally leave them pretty rough with circular machining marks left.if you burnish out/polish out the rings and get it gleaming then miraculously the true flow rate is achieved.dont change the shape just polish it up till rings about gone.easiest way is whittle a piece of dowel down to right size and with jet held in the vice practice on trying to light fires without matches.-i.e. spin dowel,with a wee bit of tcut or similar in the end of the jet.polishes up in seconds-or simply burnish it if you have some dentists tools etc.then max flow achievedclap

ferguson

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Anderzander
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August 31, 2016 - 9:09 pm
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I handed my spare D1 head to an engineering friend tonight 🙂

looking in the barrell tonight I was surprised how much carbon is in the barrell - the plug is a nice chocolate brown though. The transfer are almost uncovered at BDC.... and I've already mentioned the inlet isn't quite uncovered at TDC.

So I'm thinking I might run it with no head gasket, two base gaskets, and take some off the bottom of the piston... and the head done too of course.

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ferguson
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September 1, 2016 - 7:52 pm
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so more torque with barrel lifted a touch and quite a lot more oomph with head gasket in bin and head skimmed-losing head gasket more than compensates for added base gasket-infact you could add one or two more or get one of the trials ones which used to be about 1mm

ferguson

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ferguson
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September 2, 2016 - 2:07 pm
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finally got to test the 'modified' 361 carb.it fired up first kick and settled down to a perfect tickoverrofl.it sat for 5 minutes ticking over before i decided that it was time to ride it.main jet is approx an 80 or 82 tops and needle still 2nd from top .well it set of like a startled ferret.romped up to 35mph in 2nd gear and was pulling way better in top.have not gone for a top speed yet as wanted to do a plug test first and its a light chocolate compared to a slightly darker chocolate as in standard format.however it effortless cruised along 5mph faster than it did before.much more oomph.will see how it gets on with a longer run before i change any of the settings but pulled well on full throttle up hill and did not find it easier if i gave it 3/4 throttle so main jet near enough spot on it seems.if i'd drilled it at 17mm instead of 18 i'd guess it would probably stall if throttle shut but at 18mm it has a perfect slow tickoverdoh

ferguson

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grubsie
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September 3, 2016 - 6:25 am
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OK. Trying to simplify this topic for myself. I am a show me type of guy and not very good at reading and applying kind of guy.

Since I am across the pond in the States, finding one of you guys to show me isn't an option so I will explain back how I understand the conversation so far.

1) Make sure that the piston skirt at TDC fully clears the top of the intake port. Mod to the piston skirt to accomplish this may be necessary. (Wouldn't that mod to the skirt change the timing as to when the full close of the intake should happen?) Mods to the intake port a better option?

2) Make sure that the dome of the piston fully clears the bottom of the exhaust port at BDC. Slight mod to the top of the piston if needed. (Wouldn't that mess with the timing as to when the exhaust should start leaving the cylinder?)

3) Make sure that the fit, inside of the carb to the intake stub of the cylinder is a smooth transition. Some grinding may be needed on the cylinder stub.

4) Resurface the cylinder head to reduce the volume of the compression chamber for higher compression. Throw away the cylinder head gasket.

5) Match the transfer ports of the engine casings to the cylinder. Some grinding may be needed.

6) Carb jets may need to be made once all the above is done.

7) Throw away the D1 engine and retro fit a Honda 750 four cylinder engine into the the frame. (Just kidding).

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cocorico
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September 3, 2016 - 8:01 am
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grubsie said
OK. Trying to simplify this topic for myself...

1) Make sure that the piston skirt at TDC fully clears the top of the intake port. Mod to the piston skirt to accomplish this may be necessary. (Wouldn't that mod to the skirt change the timing as to when the full close of the intake should happen?) Mods to the intake port a better option?

2) Make sure that the dome of the piston fully clears the bottom of the exhaust port at BDC. Slight mod to the top of the piston if needed. (Wouldn't that mess with the timing as to when the exhaust should start leaving the cylinder?)

 

I intend trying these mods, and I will start by working on the piston, as described, - mainly because if I get it wrong, a replacement piston is easier and cheaper than a new cylinder!

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Anderzander
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September 3, 2016 - 12:50 pm
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I think you can get good gains without touching the cylinder - making sure all the ports are fully opened is in effect blue printing it. Doing the head is relatively straight forward as they are easy to come by and easy to change. I'll take pictures of mine as I go.

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ferguson
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September 3, 2016 - 6:07 pm
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if i wanted a nice crisp perky little bantam -this is how/what i'd do.

firstly just radius all the sharp edges on the ports-if only to extend the life of the rings-and then make sure cutaways on crankcases match the barrel.then make sure bottom of piston not masking the inlet port at tdc[cocorico-shortening the piston right round actually helps the timing as gives a dwell period but just easing bit masking inlet port does nothing except let it breath better-can explain dwell period if that helps you get your head round it]

then IDEALLY the piston top edge is spot on with base of exhaust port at bdc.smile if just below and bring port down to level.if above just a wee bit off the piston edge in the area of the port sorts it but lifting the barrel does too.if you lift the barrel you alter the whole of the port timing -more torque but slightly less go go .-which is why trials bikes done-its horses for courses and most people get 'queasy' about attacking the piston but it is fine to do so if you choose that option.[i found that worked best for a road bike]

skim head[if got an early head just smooth the angles round the plug as quite sharp and can cause pre ignition when hot-later heads have this done at factory.]and get a wee squish band machined in.

get crank alignedsignprettyplease_gif.do it last and handle with kid gloves once done-just dropping it on the bench a bit clumsily can throw it out by lotsa thousands-and put whole back together.clap

i personally would bore a 361 out to 17mm and put a taper on each end to create venturi-did ten miles on mine this morning and a big grin on my face the whole way.then ease the inlet port to match.

that will give you a perky bike that isn't quite such a liability in traffic and great fun to play on with probably better than factory fuel consumption.-and you have done nothing to overstress/interfere with the overall integrity of the bike-more just done what bsa should have done!

ferguson

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ferguson
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September 7, 2016 - 2:58 pm
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finally set the carb up properly.was running ok but felt a little light on power at full throttle even though plug looked fine.raised the needle and that only made it 4 stroke more at light throttle openings so next tried the needle jet.got a 107 in stock so swapped it for the 106 and it just made it 4 stroke throughout the entire rev range as increased fuel supply at all stages of throttle opening.so went back to the main jet and increased it just a tiny amount[wound in reamer just an 1/8th inch more than it was before] and it now it revs cleanly at full throttle and pulls well up the hills-infact it will now get up one in 2nd that has always been a first gear grind.

wee bit of 4 stroking on part throttle and light loads but i approve of that cos its cooling the piston down while 4 strokingclap.

overall taking carb out to 18mm has improved acceleration and lets me keep up a higher average speed.top speed in first and second is higher but very little in it in third gear-i presume the deficiencies in the porting are too big a hurdle for just tweaking the carb to overcome.next week i'm going to find time to treat it to a new little end bush so will properly check out the ports and see how worn the bottom end is.just looking for an excuse really to pop out the crank and get it aligned/balanced[but it really does need a new little end bush as starting to tinkle on light throttle settings-honest].

ferguson

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Anderzander
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September 9, 2016 - 2:49 pm
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Ferguson 😊  I've made a start ..... Have a look in my thread: [Permission to view this media is denied]

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