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Post by Monglord on Thu Jan 10, 2019 7:14 pm

In readiness for the FuP and maybe R&S I've finally started looking at getting the pitbike running again.

Having bought an original Honda C50 engine (complete minus piston/ carb/ exhaust) for £20 at the R&S autojumble last year (well spotted EsoX- seems like a very reasonable price to me) I've had the head off to start investigating.

Rewind to R&S 2015 and some unknown numpty thrashing it around the field for ages in 1st gear after I'd torn the meniscus ligament in my right knee coming off it and couldn't care less about it right atm.
Turns out the inlet tappet lock nut had come loose and fallen through the valve gear which ended up bending a valve- hence no compression.

Fast forward again to summer last year and VJ made a herculean effort to get it running only to find the issue I've just described after having swopped the stator plate to sort one of my previous fuck ups and fiddled about trying to get it to run for ages on one of the hottest days of the year.
(Btw VJ, remember you weren't convinced there was a spark once you'd soldered the new stator connections? I had a look at that and I think you may have had one of the wires connected wrong, one that wasn't actually soldered?- not a criticism, just saying.)

So having removed the head from the Honda lump and cleaned it up I noticed a couple of differences:
a) The Honda engine is 49cc compared to 48cc of the Chinese one (marked '48ml' incidentally).
b) The valves in the Honda are two diff. sizes- inlet larger than outlet (quite a pronounced difference), in the Chinese head the valves are both the same size- incidently slightly larger than the inlet on t'other head.
c) The diameter of the inlet tract (where the carb joins the head) is drastically smaller on the Honda lump compared to the Chinese one.

Anyone have any thoughts on any of my findings?
With my limited knowledge I would expect it to run still even with these differences.

The Honda head will go on the Chinese barrel- will the (supposed) capacity difference matter?
I'm guessing the fuel/air mix won't flow quite as well if there's a sudden reduction in the inlet tract?
Maybe all it'll need is a fiddle with the mixture screws?

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Post by virusjohn on Fri Jan 11, 2019 10:32 am

yeah I cant remember what I had for breakfast yesterday, fucked if I can remember a colour code for 2 chinese pitbike parts Razz if I left one unsoldered and you hadnt run out of solder I would guess I was unsure about the connection and didnt want to make it permanent though.

Capacity difference is negligable, I wouldnt expect major compression changes there. If you were really anal you'd measure the combustion chamber volumes on both heads but Id be very suprised if it mattered. Especially if the piston at TDC has the same height exposed/not exposed above the bore (Crown height above headgasket face)

smaller exhaust valve = better breathing at high rpm rather than low down torque. Probably good for something thats going to live fairly high in the rev range anyways.

aside from carb fitment issues the only real change inlet tract length does is move the peak torque around the rev range, shorter intake tracts push the peak torque up the rev range.


I expect you might need to fuck with the idle screw and mixture screw to hold an idle but overall I wouldnt expect much problems (apart from that fucking wiring).


Have you worked out that honda design better heads than the chinese yet? Razz

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Post by Monglord on Fri Jan 11, 2019 12:43 pm

Cool, thanks for the feedback- much appreciated.

Re the wiring you were doing I did wonder if you were leaving it that way deliberately.
I can see from what you're saying about the valve and inlet tract differences that the Honda was designed for road running and the Chinese for twatting about off road- seems to make sense.

Thinking about the capacity difference, the piston crown doesn't breach the head gasket face so that should be ok.

The carb should fit fine and the difference in bore where the carb inlet meets the Honda head is a reduction of only a couple of mm, the original Chinese head was a good 8mm bigger!

I've now got the head totally ready to fit and soldered the wires for the stator.

Next is to check wiring for continuity then fit the head and time it up/ set valve clearances before spinning it over in the hope it sparks.
Then drain what oil remains and refill before fitting the carb and bodging the throttle cable back into action.
After that it's refitting tank and seeing if the bugger'll start.

Progress will continue at the w/end 'cos I've now got to see if I can get my washing moshine to work- joy.


Last edited by Monglord on Fri Jan 11, 2019 12:50 pm; edited 1 time in total
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Post by virusjohn on Fri Jan 11, 2019 12:48 pm

make sure you crank it over slowly by hand at least 4 rotations to be sure its all good before you try and start it. if youve fucked up and got a valve meeting a piston its better to do it slowly at spanner speeds where you can feel the resistance and stop rather than 6 foot of knobhead jumping on the kickstarter Razz

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Post by Monglord on Fri Jan 11, 2019 12:54 pm

Good reminder, thanks.

I'll even splash out £14 on a new kick starter for it if it's a runner! Shocked
(The one off Maxs PY is a proper ankle grazer and he'll need it to start his- the plan is that we can ride together if mine runs.)
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Post by esox on Fri Jan 11, 2019 4:58 pm

Aye, just bolt it all together and carefully turn it over (plug removed so you don`t confuse compression with any valve/piston interface scenario) then a gentle kick (starter).
So the valves on the Chinese head are both larger than the Hondas? Interesting, i suppose it`s tuned for a slightly more sporty power delivery, the Pit with the Honda head may make it a bit tamer which is no bad thing - less potential trips to A&E after unplanned monowheelery...


Whats the matter wiv the white goods - i used to be a washing machine repair man in a previous life..
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Post by Monglord on Fri Jan 11, 2019 6:30 pm

Yes, even with only 48cc of POWER the little beast was very torquey- short wheelbase probably exaggerates it.
Mind you if there's potentially more top end (hahaha) that's not great for the sphincter muscle as it was proper squirrelly at speed, maybe the worn out knobblies didn't help but I suspect the size and weight of the rider had more bearing on it.
I never got to do a satnav measured top speed run before but I'd like to try at R&S maybe.

Washing machine repair man! (read in Monty Python Bicycle repair man style)

It tripped the fuse board part way through the cycle so I called the local appliance shop monkey out- ever heard of mechanical sympathy? No, neither has this bloke- should have been a blacksmith I reckon although that's doing blacksmiths a disservice.

Anyway he diagnosed a fecked heating element- £30 call out charge + £80 to supply and fit the element= me finding the part on eBay for £17 delivered and fitting it myself thereby saving ££s Very Happy
The element was properly caked in limescale and gunk so I can see how it might be knackered although without proper electrical knowledge I don't know if it was the thermostat in the element or the element itself?
There was continuity through the element although who knows what that means- it's all smoke escaping from tubes in my eyes. Neutral

I'll plumb it back in tomorrow and providing that was the issue all should be good.

While you're around did you catch wind of the possible change of FuP date?
Also you bringing your pitty? There's scope to use it at this site Smile
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Post by virusjohn on Fri Jan 11, 2019 7:17 pm

I wanna see esox on pit vs hoon on pit vs mouse on electric powered fucking death machine :p

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Post by esox on Fri Jan 11, 2019 7:56 pm

I did our WM heating element last week - mine was open circuit (water not getting hot) but also caked in shitey limescale. Well done for fixin` it yerself. (diagnosed by third party, though...) I was going to suggest element as first thing to check on an earth leakage fault..
****Washing machine chat on Ratbikezone****

Have you settled on a Fup date yet?

Pit is only trailerable on the CBR which is un-MOT`d at the mo, but i might know of a cunning temporary plan to work around that Idea - let me know if your PittyMcPitface is a goer first, though.
I`m sure my 125cc pitty has more potential speed available, i`m thinking of a sprocket swap and maybe bigger carb to unleash it`s full potential, it runs out of speed really quick and first gear is almost useless it`s so low.

Let the games begin.....




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Post by Monglord on Sat Jan 12, 2019 8:59 am

It's times like this that I wish electrics and I got on better, I did a week of electrical training in my apprenticeship but it never really sank in or 'clicked' with me.
So what is it about a heating elephant that causes the open circuit?
It was the first thing the 'engineer' (oaf) checked so I guess it's a common fault.

Currently waiting for Mouse to get a date from the social club for the FuP, I'm hoping we can have the original date 22nd-24th Feb or the following week 1st-3rd March- any later than that and it's more of a SpringUp but no worries.

What's your pit like at speed then- any death weave?
Is it 4 speed? Mine's 3?

After a little research it seems like that engine I bought might be an 'Economy' model with 4- speed box.
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Post by Monglord on Sun Jan 13, 2019 12:12 am

Washing machine- fixed.
Saved £63 by fitting the new part myself- fuck the heavy-handed mother fucker who comes to mend stuff Cool

Back to the pitbike:
Tried fitting the Honda head to the Chinese barrel but alas the piston hit the head.
I'm currently trying to find out the piston diameter of C50/ 70/ 90s 'cos I'm not convinced the pitbike is a 50 due to the difference in bore between the Chinese engine and the Honda.

Next step is to try and order a replacement valve for the pitbike head and be done with it.

I'm looking forward to making my own valve compressing tool, it's an interesting project overall.
I have scavenged a rocker adjusting screw and lock nut from the Honda for the pitbike so it's not been a totally wasted purchase- the spare engine also potentially provides spares for the C100 waiting in the sidelines.

I will get this feckin' pitbike running again!!!
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Post by esox on Sun Jan 13, 2019 6:19 am

Does the pit not have the cc cast into the side of the base of the cylinder?
Does the piston reach the top and is level with the top of the cylinder at TDC?
If so measure the where the piston is at BTC - you`ve got your stroke, then.
Then measure bore diameter and work out cc from pi r squared x stroke. I`d be surprised if it was a 50 as it had some poke i seem to recall.
Pitbike spares are rediculously cheap, a complete head is prob only about £30, the trouble is knowing exactly what engine/make you`ve got there`s so many knock-offs.

Shame the Honda lump isn`t usable - maybe you could improvise some use for it next time the washing machine needs fixin`.
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Post by virusjohn on Sun Jan 13, 2019 11:54 am

im probably missing something here but why not bolt the c50 in complete and ditch the chinky motor?

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Post by Monglord on Sun Jan 13, 2019 12:12 pm

The only marking on the cylinder is '48ml' whereas the Honda has '49cc' in the same place which I thought was a chinglish way of saying 48cc but am now inclined to think is the diameter of the bore having measured it and it being 48'mm' (so 'ml' is chinglish for mm it would seem).

Yes it is, after looking on eBay I found a piston for a C70 marked as 48mm (+1mm oversize).

So owning a chinky pitbike makes for interesting detective work and dangerous fun Smile

After investigating the gearbox on the Honda lump I think I've found out why it was so cheap, 2nd gear feels very crunchy and jumps in and out- it definitely has issues inside it's metallic little body!
Worth having on the shelf though as possible spares for the C100 I reckon plus I got the all important tappet adjuster Pitty needed.

4stroke washing machine Laughing
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Post by Monglord on Sun Jan 13, 2019 12:26 pm

VJ- that's always an option I suppose but it's missing its piston (which I knew about) and as I discovered yesterday 2nd gear is fecked.
Nothing to stop me trying to sort all that out or cobble Pitty gearbox parts into the C50 cases but I'm thinking a new valve will be cheaper and quicker to sort.

This is meant to be a quick project for fun at the Fup/ R&S, my main priority is getting the CBR back on the road 'cos I REALLY miss riding a solo!

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Post by virusjohn on Sun Jan 13, 2019 8:25 pm

if you wanted to be a complete reckless nutjob you could but a YX190 engine in that makes 18bhp lol





i mean its about 800 quid for that engine but thats a lot of shits and giggles watching people punch themselves in the face with the headstock whilst you sit and drink beer right?

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Post by june_whitfield on Mon Jan 14, 2019 3:34 pm

Jesus H. Christ, that thing is turning into "Trigger's Broom"

surely you can get a whole entire new pit bike for £12.99 quid on Chinese Ebay!
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Post by Monglord on Tue Jan 15, 2019 10:50 am

Update:
Just ordered a complete set of valves and springs/ collets/ seals from Amazon for £7 which should arrive just in time for FuP.

Esox- I'll let you know as soon as I have it running.
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