Honda MB80-H100a?

[Piercee100]

Could anybody confirm or deny that the Honda MB80 / MT80 is the same engine as the H100a (MB100) engine? I believe I read somewhere that they are but not the same as the later H100's.

Reason I ask is that I found this whilst trawling the web and was curious whether it could be bolted onto my H100a giving me a genuine 70mph on tap rather than the 67.9mph i'm getting at the moment.

https://www.vsmotoparts.com/brands/honda/mb80/athena-cilinder-125cc-honda-mb8-mt80
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Rides: Honda H100a (Retired), VT500e (Sold), Kawasaki ZX400 (sold), Kawasaki GT550 (Sold), Suzuki Inazuma (Daily), Honda CD185t (Broken), LML Star 2t (Last run edition).

[truslack]

is it worth all the hassle for 2.1mph?!
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Current: Suzuki RG 125 Gamma, Honda H100, Triumph Tiger 800XC, Suzuki SV650 (minitwin)

[Teflon-Mike]

Curiousely enough.... er NO they are NOT the same engine. Clue is sort of in the fact they have different capacities and different numbers.

HOW different they may be and whether they share any common components, now THAT is a SLIGHTLY different question.

May be that they share the same crank-case castings, and are interchangeable between frames, which I THINK is true for the MB50/80 & H100.

How much inside may be the same, very different matter, Could have different cranbk shafts for different strokes, almost certainly different barels and different pistons to get the different capacities, whether the barels are on the same flance patern and are interchangeable, I wouldn't know, nor whether the pistons would be interchangeable on teh con-rod.

But swapping entire 'lump'... be more concerned with things like the kick-start and the out-put shaft.

Quite likely, gearbox ratios are different inside, but on a swap, it will be the length of the output shaft and where the sprocket sits that's likely to cause a problem, likewise kick-start and kickstart shaft.

Other one is where the exhaust port is located on the barel, and possibility bigger motor uses bigger pipe, or is mounted higher, or at a different angle to clear frame rails in intended frame...

Then in alternative, where exhaust lines up with mountings, clears foot-pegs or fould stands etc.

Which exhaust do you use, one that fits bracketry on bike, or one with resonance tuned to engine porting?

Offer enlightenment?
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[cb1rocket]

it will go slower, true speed is just on above 58mph on a proper measured speed run for the H100. Speedo is over reading as per usual.

Only upgrade to this, which I have tried to do is change the reed block for a freer flowing one and a custom exhaust upgrade.

Only way to make these things quicker!

[Piercee100]

I've tested mine with a GPS for a laugh and it did genuinly hit 66mph and the speedo registered 69 so its not so far out actually and thats with 15 stone me on the bike laying across the tank. Honda claim with their gearing 77mph is possible but that must have been in a wind tunnel or something with no load.

Exhaust is easy, since I've researched and the MB8 and H100a versions have the same size outlet and fortunately their are many performance exhausts for the mb8 (one I was looking at suits engines 80cc-125cc) its just a case of creating a bracket which is a few inches further forward to make the rear mounting fit.

Carb is also easy since Molassi do a replacement carb kit with manifold and reed block and has a selection of jets. Gearbox from a mb8 also fits in the H100 case giving six speeds which the Australians use in their bucket racer series and again seem easy enough to obtain.

My question that I cannot find any answer for on the web was simply whether that 125cc cylinder head and piston (designed for the MB8 block) would fit on my H100a block. I'm guessing its a no because somebody would have done it by now but it seems that europe didnt have the H100a where the MB8/MB5 is popular with their moped laws and the Australians didnt have the MB8 where the MB100 (H100a) was popular and we... Just get a bigger bike.

So why bother, get a bigger bike. Simply this, I have a brick shed behind a steel gate which is 3.5' wide and then down an alleyway beside my house to my 5' X 4' brick shed and the H100a fits inside at an angle perfectly. And due to living in a pretty rough area (looks like the estate out of Only Fools and Horses) I have a lockup where I keep my other bikes but is 3 miles away and because I'm lazy I keep riding the Little bike because its closer to me, more reliable and cheaper to run. Friday I rode the little Honda 2-up for 160mile round trip. It did it well, averaging 55mph and cost me £9.75 in fuel. I even came home 2-up via a downhill stretch of the Motorway at 65mph indicated and was overtaking. Only downside was the numb arse, white knuckles and a sore nutsack. Wife on the back thought it was hilarious.

So the little H100a serves its purpose well and could be more useful to me if it was a little quicker. being able to pull a larger sprocket and sit at 70 would be useful, cruising at 65 would be nice.
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Rides: Honda H100a (Retired), VT500e (Sold), Kawasaki ZX400 (sold), Kawasaki GT550 (Sold), Suzuki Inazuma (Daily), Honda CD185t (Broken), LML Star 2t (Last run edition).

[cb1rocket]

[stevo as b4]

I think it is impossible for any tuned 2stroke exhaust pipe to closely suit any capacity from 80cc to 125cc. Engine capacity and expansion chamber volume are very closely related. Fit a big bore kit to a 125cc that takes it to 150-160cc, and while the extra capacity will give some power and torque improvement. The tuned length and the volume of the original exhaust system, will not suit the bigger capacity motor, and it's most likely that the top end power will be mostly affected.

If i remember what Keith said, the H100 has very low gearing and makes maximum power around 11bhp at 6800-7000rpm. to even get to 65mph it is revving quite a bit past peak and so the power is dropping away fast.

I think a custom expansion chamber, some reedblock mods and a clean up of the porting is probably the best way to get some extra go out of the H100, but even with these mods you might need to look into options for raising the gearing, which might mean custom sprockets. Did you say you can fit a 6speed gear cluster into the crank cases? if so that might be one answer.

If you wanted alot more performance then you would probably find the MBX80 liquid cooled engine can be tuned much further and easier with big bore kits and aftermarket parts etc. The performance and reliability would probably be better than a messed about with H100 by a long way too IMO.