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Repair-Honda Engine with box of parts...

This is a discussion on Repair-Honda Engine with box of parts... within the Honda forums, part of the Manufacturers category; Great thread. Being a new owner of a '76 XL and having spent the last few months learning about Honda ...


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Old 07-22-2012   #11
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Great thread. Being a new owner of a '76 XL and having spent the last few months learning about Honda 125 related expectation/disappointment, I read your process with interest. I bought the bike on the strength of the sellers intimation that it had recently had a top end rebuild, which may have been so. Nonetheless on it's first excursion post cleanup and tuneup it seized. Teardown revealed a mess. Had 1mm oversize piston and bore but rings seized to piston and piston/bore ruined. Extracted a ring, inserted it into bottom of bore, lo and behold zero gap between ring ends.

So bought two parts engines supposedly 125s, one is a six speed, turned out to be I think from an XL100, but has the same rotor/stator as yours.

I don't have the CDI controller or pulse generator, and as the alternator wires had all been cut just outside the left crankcase cover, decided to experiment.
I put a points housing and points on where the pulse generator goes, hooked them up to the black wire and it seems to generate plenty of spark and runs well.
I tested the other wires, not sure which is which but at idle one presents about 6.5V AC and the other about 14V AC. Will try to find a suitable zener regulator and hook up the low one to charge my battery, and maybe get a 12V headlight bulb to make use of the other one.

Ben
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Old 07-22-2012   #12
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Also, I think that your engine is very similar to that of an XL125, principle difference that I can see being the head. Yours has the 384 stamp, smaller valves and chamber than the 383 head which apparently was maybe the main upgrade the XL125 engine received upon evolving from the SL. The 384 head was still used on the XL100 though. I've deduced that my XL sadly had it's engine replaced with that of an SL, and haven't yet been able to find an actual XL engine. I can only imagine the joys of the gut-wrenching power produced by the larger valves..

Ben
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Old 07-25-2012   #13
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Very interesting insight,

I did get a spare head in the box of parts. I didn't consider it at the time, as the engine had a head on it and I considered it complete. This spare head has the "mounting-eye-hook" on it, that I've seen in every picture of the XL. It is complete with valves etc.

So, you're saying that this other head should have larger valves and a larger chamber...lower the compression ratio? I will go out and look at it to see if it has the 383 stamping...

If this is the case, would swapping in this head produce more power?
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Old 07-25-2012   #14
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Well I certainly think it'll increase it's potential flow. Of course if the inlet manifold is tiny and or badly matched to the head it'll not make a lot of difference, also the carb throat size will have some bearing on that as well, along with the exhaust.
As for the compression ratio, I'm not entirely sure what the original piston profiles were for the different models, but I've found a number of different ones in the parts motors I've acquired. I have one which has a slight dome with valve recesses which I think is probably the OEM for the XL125, but I've also got a flat one and one that is kinda concave. The Powroll website has a tech article saying that the compression ration doesn't make a huge difference to power, within reason I guess.
I also suspect that the chamber isn't much different in volume overall, but is definitely has a larger diameter at the mating surface with the cylinder. The 384 head has a combustion chamber which is the same diameter as the 100cc cylinder.
All of this is just research based speculation on my part though, as I haven't got a 383 head to compare/try for myself.

Ben
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Old 07-25-2012   #15
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Ha, ha...I like this:

"All of this is just research based speculation on my part though"

Is there any other kind? he..he..Maybe direct designing info from the original head tech; who's probably long since dead...

This is the first I've heard mention of the head numbers and any related designing, so, you're research seems to have paid some dividends..

Interesting that you mentioned the carbs, as I did get two. The venturies are the same size but the noted difference is the plunger size. One is bigger than the other and are not interchangable but, the main needles are; they are identical. The rest of the carb also seems to be identical, with the exception of the idle jet. One was removable, while the other was not. The manuals I have mentions this fact (idle jet) in passing, attributing no special significance to this fact.

Too bad about you're rings...can you believe I've seen this in big blocks as well. Sometimes learning costs money. The rub here, is that it cost you the money, and the seller learned nothing...
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Old 07-25-2012   #16
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:) well I can easily speculate without research and possibly sound believable but I wouldn't be able to sleep so easily. Also I've noticed that assumptions have a way of ingraining themselves into the psyche, from which I potentially end up making bad decisions based on my own bullshit. Best avoided.

Mine originally had a badly corroded 24mm throated carb which I swapped for a 27mm chinese one, with a noticeable power increase, but that was with the 1mm oversized bore which took it to somewhere around 127cc from 124. Having now rebuilt it with a standard bore I found that it didn't run so smoothly at low-mid revs. Reconditioned and refitted the 24mm carb which made a huge difference. So it seems there's apparently a very fine balance to be found between all of these flow variables.

Yeah, it's frustrating to know that I'm the sucker in the end, but on the bright side I've now learnt plenty about these motors, and I've got enough bits to make 4 good recon'd ones eventually, which I think should sell for around NZ$500 each, hopefuly recouping my loss.
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Old 07-25-2012   #17
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...


Yea, I'm the same way. I don't have any respect for people that BS their way through an opinion just to be right for the sake of being right. Like a politician, they would rather have a majority agree with a contention, than a minority; regardless of whether that information or contention holds any weight when put up to the evidence of experience, wisdom, or proof.
I consider it a waste of my time...like politicians, best avoided.

Actually busy with other things right now but I'll get back to her next week. This is the bike that it will be going into...





The whole thing got started because I just happened to put my spare tire in the right place at the right time...





Then the piston started to rattle...again. So, summer project...


...
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Old 07-25-2012   #18
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Ha, that's brilliant. That picture has done a lot to brighten an otherwise rather dull day at work. Thank you sir.
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Old 07-26-2012   #19
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No worries, Batman Bike...

It's all just for fun anyway, but it's got to be real.


I think Honda made something similar in the mid 80's for the North American market...
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Old 07-27-2012   #20
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Yup, Honda called it the "Fat Cat", AKA, TR200, 86 and 87 only...

As far as what I have; my spare head is an "E-2", NOT a 383...(for the XL)...
Has the weird kind of mounting bracket, but, looks like, smaller valves, and smaller spherical chamber...Maybe for a 100cc...?

Go figure...Still thinking, still working, still asking for help...


...
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