Opinion on engine choices?

BobbedSled

BobbedSled

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I have a 1971 motor pulled from a running bike with 34,000 miles on it from a reputable moto recylcler on ebay with 99.6% and well over 10K items sold. Full rebuild should not have too many surprises I would guess. I have all new Koyo bearings top and bottom end already for any rebuild btw.

I figure buying a newer motor of unknown state could be a gamble. I could buy a running bike but even then it may need top end and seals after all this time but that would cost as much as a rebuild of my 71 motor before I did any maintenance.

If I rebuild my motor competently top to bottom, would those in the know be saying I should have used a newer motor to rebuild. Is there any reason to a source a newer late model motor over an older one that I have? Is a late model motor have an advantages assuming both use Pamco and same Mikuni carb set ups?
 
Parts for the earlier bikes, 70-73 are harder to find. These are the 256 engines.
The 74 up used the 447 engines. The 256 engine has a needle bearing in the small end of the rod. This makes the walls around the bearing thin. This lets the end of the rod go egg shaped when ran hard.
In 74 they deleted the needle bearing yet used the same size piston pin. This made the hole in the rod smaller, so the walls were thicker, no egg shaping of the rod on hard running.
The earlier 256 engine head different head specs, valve angle, port shape and some other things that let it squeak out a bit more power.
As gggGary mentioned the main reason to keep the 256 engine completely 256 is for the looks. With all four valve adjustment covers just three holes, 70-71 and the decompressor, 72-73.
Now you can swap the internal parts from the 447 into the 256 and keep the look.
Everything, crank, cam, cam chain and tensioner all swap as a unit.
This is a bit of work but some feel it's worth it.
Any way you rebuild your engine, if properly maintained and not beat it will hold up fine.
Leo
 
Funny thing is I learned all this 2 years ago then forgot it as life got in the way. Now I am back to finish by build, this all rings a bell. Thanks for the info, I may just look to source a mid 70+ motor with low miles if possible.

Thanks cheers!
 
77D should have "points, advance rod and advance unit" already in it. If not, why. make sure it is a 77 engine, if not, and its 80 and later the cam will need bushings.
 
From what I have learned yes. They are all the same, its just that the TCI bikes (80-83?) did not have them.
 
Yes, but as a caution, the cams for the 80-84 models have to have some work done to receive the bearing, if not and the bearing is forced it will split the end of the cam.

Have you checked the engine no?
 
Right, ENGINE# 447-720328, I looked up the part number and it lands IT3 at 1977.
I assume the e-advancer has advantages over mechanical. This is the Pamco kit for the motor ya? -> https://www.mikesxs.net/product/24-2613.html

$_57.jpg
 
Tell me this, if you can, if rewinding the stock unit and using that works with aftermarket regulator/rectifier and coils then why not do that? Is there something else that the aftermarket PMA'a do that a rewound OEM alternator won't do?
 
Yes I hear you, I suspect not, clearly not made in the USA or Japan, this is the reason I spent the last 12 months sourcing every bearing and bushing internal to the engine from Yamaha or Koyo. No way I'd stick Taiwan or Chinese bearings in there. I get it.

So my question is, does rewinding stock stator accomplish he same thing? Basically just buy everything but the PMA and have the stock stator rewound. How is it functionally different than a rewound stock stator. The name PMA implies that it is somehow different.
 
Why not do a diy retrofit PMA kit, but use a brand new OEM stator, or an aftermarket USA made one?
 
I'm very happy with my 256 motor with a 447 tranny installed. My PMA works great in my motor. A pma puts out more juice and is able to run my motor with no battery and only a small capacitor. No issue with the lights being too dim at idle. They do dim a tiny bit but not excessivly.
I would like to rephase it when funds allow.
 
weekendrider, I just bought the motor I don't know, but in general I think I just want one. I am going to use a battery also mainly because the frame is so big I had to put one there to take up space. More I think about it it seems like what Terrible1 says is where I landed as well in my thinking. Get a PMA kit get it in to get the bike working then have a stator rewound or use a Banshee stator or what and swap them not as a second step.
 
You can get the bike up and running without the charging system. Get the Pamco, get the bike running on the battery.
Between now and then read up on the stock alternator and the PMA.
Just to add a bit of info, the stock alternator is a Field Excited Alternator. It uses battery power to create an electro magnet in the rotor to excite the stator to make electricity.
The PMA or Permanent Magnet Alternator uses permanent magnets to excite the stator.
Use Google to find more info on these types of alternator.
The only advantage the PMA has is it doesn't need a battery to function. Others will say the PMA is more powerful, less maintainence, yada, yada, yada. All just hype to sell PMA's.
The only maintainence the stock system needs is the brushes changed every 5 or 6 years and keep a good battery in the bike.
Leo
 

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