Best engine year

acebars

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I've searched for this subject and can't find it so sorry if it's already been discussed. For the uninitiated what is the best year of XS650 engine and why? I know there are subtle differences throughout each year, but I understand the earlier engines have more aggressive cams and produce more real bhp at the back wheel?

I have a '73 bike on it's way but I've been thinking of buying another engine as a spare to work on while I ride the other, this is what I've done before successfully with previous bikes. So would like to look for the right year.

P.S. I will be stripping the electric start and running a magneto setup so e-start is not a consideration for me.
 
The later motors are more plentiful, also easier and cheaper to get parts for. The old ones have a design weakness. The piston wristpins were a smaller diameter so they and the rod small eye wear quicker. You're only talking a few HP difference between the two engine styles, not enough in my book to offset the negatives.

You can swap an early cam into a later engine if you change the sprocket, something I'd like to try some day. Also, the early heads are supposed to be ported nicer. I wouldn't mind trying one of them as well. What I really need is a 2nd 650, lol. A test bed for all this stuff.
 
Has anyone tried this on this forum?

So a later engine with an early head and cams? (What is considered early?) I mentioned before I have a '73 is that early?
 
Yes, '73 and earlier are what's called the "256" motors. '74 and later are "447" motors. In Europe, they also got a variation of the 447 which is called the 533. It had different length rods and different pistons. Not sure why they did that.

I know a few people have done the head and cam swaps because I've seen them mentioned on these forums. That's where I got the idea for trying them. The cam sprocket is pressed on so swapping them is probably beyond the capabilities of most home mechanics. Besides the pressing part, you have to ensure it's aligned properly so the cam timing is correct too.
 
So early heads/cams must be rare finds? Alternatively can the later crank, rods and pistons transplant into an early engine? Or are there other shortcomings of the early engine?
 
Well I have found some threads but the information is conflicting/confusing:

256 vs 447? Here we go...

447 rods onto 256 crank

Apparently the wrist pins are bigger not smaller on the older 256 engines:

inxs said:
- the numbers are cast into the conrod
256...136mm conrod, 22mm wrist pin, 26mm crank pin, no starter cog...306...same with a starter cog
447...130mm rod, 20mm wrist pin, 26mm crank pin, starter cog
533...140mm rod, 20mm wrist pin, 29mm crank pin...mostly sold in europe

From that data, I'd prefer to stay with a stock 256 over a 447.

So still would be nice to hear what the negatives of the early engines are? So far only positives compared to the newer ones as far as I can see.

I like a torquey engine so I suppose the 533 looks like the best crank/rod for me.
 
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In my limited experience,(motors from72, 73, 75, 78, 81) the newer motors are less vibratory. I don't know why. Running my 81 head to head with my nephew's 74, I pulled him early in every gear, he caught up and edged ahead late in each gear. We called it a wash. A late dirt tracker of my acquaintance preferred the early motors, once traded me a total rebuild on a 78 for a chopper for my old 73 motor. Like I said, my experience is very limited.
 
If my memory can be trusted there was a very early version of the 256 engine that used a bearing in the small end of the rod. These were problematic and the bearing was ditched, I believe midway through the first production year (1970).

Parts for the 256 engines are often harder to find or more expensive when you do find them. New rods are a particular problem. Sometimes a mod is only available for later bikes, like the higher 5th gear mod. Other times you'll be told "that part works for all years of XS" and it doesn't, or it does but the fit is a bit ugly because it was patterned from a later part. It's definitely more work and surprises working with the 256 than the 447. Either one can make a good engine.
 
The XS1 "256" engines vibrated a lot but they were stronger than XS2 etc.
Some say the best - but that is only an opinion.
However the very early ones (up to engine number S650-003268) had a different con rod with a bearing at the small end which caused problems on some.
The con rod was changed at XS1 engine number S650-003269.
 
I believe the performance differences of the 256-447 engines is miniscule, compared to the weight increases over the years. I also believe the 447 superior in support and parts availability. Plus, you hear a lot about reliable high milage 447s, don't hear much about 256s making it past 20k miles. The camchain tensioner design in the later engines is also, IMO, better, as it properly addresses the chain's natural tendancy to 'fling-off' a sprocket, as compared to the earliest 256 design, which has it's lower tensioner block pressing outward at the exit side of the crankshaft sprocket.

If you want a torquey engine, your best bang for the buck efforts will be best achieved with a 750 kit, and a performance cam. The 'large fin' cylinder kit would be an excellent choice, as it also gives the engine more cooling, and, more importantly, bring it closer in appearance to the (highly admired by me) Royal Enfield Interceptor!

This kit is available in 447 configuration. But I understand that it can be done in 256 thru Hoos Racing, which I am considering.
 
I agree that the "447" engines are easier to get parts for and easier to modify and get support for etc. They are also a lot smoother.
However that does not necessarily mean they were "better" engines at the time. The XS1F engine was almost bulletproof. It depends what the individual wants. Personally I would prefer an unmodified XS1 / XS2 / TX650 around town any day. I'm sure others have different views.
There were high mileage early 650's around. I knew of one mechanic who had a 100,000 mile XS2 in the 1980's. I have a XS1F with 49,000 miles and had no engine problems (in storage since 1985).
But I think if the engine is going to be heavily modified, for whatever reason, it is probably better to buy a "447" bike such as TX650A / XS650B etc.
 
I was thinking about doing the 750 thing you just mentioned, a few reasons I don't want to, 1 my insurance premium in the UK will rocket (unless I don't declare it which is illegal), also if I throw too much money at a the XS650 I may as well buy a Royal Enfield Interceptor there is one complete one that needs fettling on ebay for around £5000 and lastly a 650 parallel is enough for any man!

Luckily being in the UK I have access to the 533 long rod engines. I'll be putting 533 crank, rods and pistons with the 256 cams pressing a sprocket over form a 533 engine, probably be upgrading the cam chain tensioner as well I hear the later ones are better.
 
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