FNG in Northeast Texas

Stubby

Stubby

XS650 Member
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Gentlemen,
It appears that I've arrived a little late to the XS party. I appreciate the wealth of information that I've gathered before I signed up. I hope I can return the favor from time to time. In a previous life I was a machinist and engine builder for about fifteen years. Been out of the business for longer than I was in it but have been craving it for awhile. After reading about the xs650 engines and the wild possibilities they offer, I purchased a used engine. Then I purchased a basket case with another engine. Trying to keep it a low buck build. Trying...….. I have disassembled the second engine, cleaned it up and rephrased the crank. The bottom end is buttoned up and now I'm going to tackle the camshaft.
MrRiggs, GGGary, Hugh, Kopcicle, Hoos and many others are to blame for my temporary lapse of reason.

Gary Stubbs
 
Indeed it is. My web searches kept bringing me here. All of the information was new and exciting till I looked at the dates of the post and then I felt like I was late to the party. However, it's new to me. The main feature I don't like about the XS650 engine is the lack of a squish band. These engines would benefit greatly from it. I've seen it's possible with the big bore kits and I will probably explore this later. I have set up dirt track motors so tight that there wouldn't be any carbon in this area.
The other area of concern is the valvetrain. Your write up has detailed it nicely. Thank you. At some point, I'm certain that I will attempt to make some aluminum rockers with a roller on the cam side. I have also wondered if those tiny hydraulic lifters from the rockers of the Chrysler v6's of days gone by would handle the loads of these springs and larger valves. It would require oil pressure on the valve side of the rocker. Or maybe rollers on both sides and move the rocker adjustment up into the rocker cover and adjust it at the fulcrum. :)
Things like these engines don't actually quieten the voices in my head. They just get the voices to talk about things that I like.
 
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I like the way you think!


borescope shot into a 750 cylinder.
2018-08-21-10-28-11.jpeg
 
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gggGary said:
I like the way you think!


borescope shot into a 750 cylinder.
View attachment 126114
Click to expand...
That's what I'm talking about. Most engines have free power and efficiencies that only require a little machine work to acquire. However, these engines seem to have engineering constraints and limited options for parts. Hemi engines have always had this trade off. Remember, I'm trying to keep it low buck.
 
Low buck would be cleaning the carbon out of the topend and replacing the rings, lol. You're a bit beyond that already I'd say, lol.

I assume you've never ridden one of these? It's a wonderful engine with great low end and midrange power. It's just perfect for blasting around locally on the secondary and back roads. It's not much for sustained high speed highway use, but it was never intended for that purpose. It's your basic, "old school" type motorcycle. It's easy to work on and there are a huge amount of little improvements you can do, many not too expensive.
 
5twins said:
Low buck would be cleaning the carbon out of the topend and replacing the rings, lol. You're a bit beyond that already I'd say, lol.

I assume you've never ridden one of these? It's a wonderful engine with great low end and midrange power. It's just perfect for blasting around locally on the secondary and back roads. It's not much for sustained high speed highway use, but it was never intended for that purpose. It's your basic, "old school" type motorcycle. It's easy to work on and there are a huge amount of little improvements you can do, many not too expensive.
Click to expand...
Having spent many years building race engines, I have learned a few tricks for squeezing more power from engines without throwing money at them. Basically optimizing what is there. This is what fascinates about the XS650. The rephrase is what hooked me for sure. I pressed the crank apart, cleaned and inspected the parts, reassembled the crank, removed all of the starter parts, reassembled the bottom end and all I have purchased so far is a seal set, aviation Permatex, and a gasket set. I will need a set of rings and maybe a timing chain and probably chain guides. Trying to resist the urge for a new performance cam, and springs and retainers and locks and, and, and...….. :)
 
Can i come back to the start of this thread for a minute. Having just bought a 750 kit I'm nearly ready to assemble I called the guy at Smedspeed, he sold me the kit, who was packing for a race weekend and I just got out the word squish when he said maybe 30 thou 40 if I was lucky.
Surprisingly he had time to add " Don't go by what's on the website that was written by my Dad and I am getting engines Dad built in from racers who can't start them."
His Dad died several years ago so if they are only coming in now they must have worked for a while, nice to know he wants to build on what his Dad learned and not just learned to build what his Dad did.
Any way I just have one question "Squish?", no two " Is there an answer already on the forum that I am too dumb to find?"
 
I have had a little success on this point, as can be seen from the image pistons supplied for enlarged bores have the squish band on the outside edge of the crown and the actual depth is governed either by using thicker head gaskets or by skimming the head to achieve the ideal depth. The vendor said this should be at least 30thou but 40thou is better.
It also needs a bit of a polish

BBK Piston.jpg
 
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