Holy Grail of XS400 Big Bore Pistons

It may take me all year, but if I go ahead with my plan to mod the bike (going to take me a few weeks to get it all back together and cleaned up), I will definitely do this!!!!

Drewpy, what was the charge for the machining from your guy...just curious?
 
Make sure you add it all up, it will get expensive quick for very little gain. It makes sense for Drewpy since he is cramming more air into the motor, and it makes sense for guys road racing since every little bit helps. But you have top take into account that you are stuck with your intake valve size and that is a huge limiting factor.
Rods will be $226 here in the states. Pistons will run you about the same. New cam grind to take advantage of it- $375. Head work- $75. Will need slightly bigger carbs- $300-500. Liners are probably a few hundred. What about big end bearings? Are you going to have the shop match them to your crank? Machine shop work- figure a hundred for the liners machined and $250 to set them in, a 'correct' bore and hone to match to the pistons is about $75 a cylinder, and taking the top off the pistons will cost you whatever the hourly rate is most likely.

Just a thought. For that much money you can buy a beast of a motorcycle. If you still want to do it, go for it :)
 
Thank you wolfe...I'm hoping to finally pick up the bike this weekend and see if I can get it running before the Florida heat really kicks in and I wont be able to work in the garage.
 
So...After 8 pages...I have a few questions:
- I have the DOHC would fj 1200-1300r rods fit..?...it would follow that the conrod bearings would fit...but they are not the same part #...:umm:
- would taking the balancer shaft out give a little extra oumf...?....is it doable/advisable?
...kinda lost track...
 
Jeff0133 said:
- I have the DOHC would fj 1200-1300r rods fit..?...
Click to expand...
Yes.
Jeff0133 said:
it would follow that the conrod bearings would fit...but they are not the same part #...:umm:
Click to expand...
The difference is the oil hole.
bearing.jpg
 
Hey everyone, especially Hey Wolfe! I registered to revive this several year old thread so you could tell us which pistons would fit onto the XJR rods since you kept it a little secret. I'm planning on upping the compression in my '79, already did an indebt head overhaul, the xs360 crank switch, so upgrading to lighter, sturdier rods would be the last thing on my list.

Much regards from Germany
Sebastian

Wolfe_11B said:
Might have found a piston that will work on our bikes with no modification, other than switching to the XJR rods. Just bought a used piston from ebay, will need to find a used rod somewhere, then I can get to measuring.

The nice thing about these pistons? They are readily available in sizes from 69 to 73mm, and can be grabbed for cheap. Only downside is having to switch the rods. But for a $200 rod change, it may be worth it to be able to use readily available, cheap pistons. Before I say what they are from I want to make sure that no piston crown modifications are needed. they do have valve reliefs, and they look right, but the angle may be totally different for all I know. I'll report when I can find a junk rod.
Click to expand...
 
young_gun said:
Hey everyone, especially Hey Wolfe! I registered to revive this several year old thread so you could tell us which pistons would fit onto the XJR rods since you kept it a little secret. I'm planning on upping the compression in my '79, already did an indebt head overhaul, the xs360 crank switch, so upgrading to lighter, sturdier rods would be the last thing on my list.

Much regards from Germany
Sebastian
Click to expand...

Rod 1TX-11631-00-A0 for FJ1200
Piston 4PU-11631-00-A0 for XJR1200
 
Time to resurrect this yet again

Have my new xs400J dohc waiting for me to bring her back from the brink after buying her for $250... very curious to look inside.
As I rebuild, and going for a tracker/scrambler type build, I'd like to plan ahead for the internals, and would love your help.

xs360 crank is waiting in my ebay cart, just curious how much worse the vibrations get? I'd like to use this bike frequently, and be okay with taking it longer distances without losing too many fillings.
I understand the pistons from the xjr1200 need to be machined down, is that the case?

Really appreciate your guys' bold dives into modifying these bikes. Very excited to start on this project. Thanks for your inputs!
 
xschris said:
Ok, this is what I would like to know. I don't think the stock stuff will work for the sizes you are talking about. I know the are a few xs650 guys boring there's out to 900+cc but they doing major machine work to them also there is aftermarket blocks that can use larger piston. And the cranks on them are custom made. I just don't think the xs400 crank and clutch setups can handle the big power jump.:shrug: Even if you could shoe horn a bigger set in there would it not be easier to get a bigger bike setup for more power? Don't let me stop ya:laugh: Like to see it:thumbsup: You do know they made a DOHC xs500:)
Click to expand...


Cool. I would like to do the same thing.
 
Not to necromance, but I've found some pistons on Ali for anyone interested. 2mm overbore, bolt to stock rod.
I am looking for a source for DOHC performance camshafts if anyone has any leads.
 

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