Stiffer Valve Springs?

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NA3S

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I'm in the process of resurrecting a SOHC XS400 and was wondering if anyone knew of any sources of stiffer valve springs, be they new or re-purposed from another bike...

As of now, the plan is a Megacycle cam, stock rockers hardfaced by Delta, gentle porting/polishing to remove castings/marks/flaws, custom 2 into 1 exhaust, and very likely different or modified carbs; opinions welcome as I'm still exploring options.

The Megacycle cam is listed as working just fine in stock heads, yet I've seen valve float mentioned as a noticeable issue in many threads I've read through; hence the desire for stiffer springs.

I had considered attempting a big bore but the wrist pin seems to be the major prohibitive element to utilizing the stock pistons and rings from another 2 valve bike; GS500/GS850/etc....

I'm not looking to spend thousands, re-invent the wheel, set any land speed records or turn this motor into something it simply doesn't have the genes to be. My goal is to merely maximize the available potential these motors seem to hold and build a fun and fairly reliable bike.

As a side note, I was also wondering if anyone knew whether or not the DOHC clutch baskets will mate up to the SOHC? It's my understanding they're 6 spring as opposed the the SOHC's 4? Will the stock clutch, with fresh plates/springs, struggle with the mods mentioned above?

Thanks!
 
The clutch basket wont work as is much larger that the sohc bikes. I have not heard of any springs that will work on a sohc motor.
 
Thanks for the insight on the clutch baskets!

I've read through that thread a few times...

Was tempted to source an XS360 crank, but would prefer staying out of the bottom end as this motor seems pretty sound with only 11,xxx miles on the clock. Although if it is as light as claimed and drops right in.....

Can anyone definitively confirm this?

In regard to the XS360, I've also read it's carbs give a nice boost in performance but they require a different diaphragm which isn't available and none of the offerings from JBM fit? Can anyone confirm this or know of a diaphragm source?

The XT225 pistons look appealing but more hassle than its worth for only 1mm over.

It seems anything else requires opening the wrist pin hole in the rod and that requires far more math than I'm willing to tackle, in addition to new sleeves and opening the crankcase spigots.

Thanks!
 
Once you have the top end off, splitting the case really isn't a big deal. And its all pretty simple in the gearbox, I was surprised how easy it was to work on the gearbox.
 
Good point, my primary concern lays with swapping in the XS360 crank, are all the bearings/tapers//seals/specs going to mate appropriately.

It appears straightforward and proven....http://www.xs400.com/forum/showthread.php?t=4854

If someone can confirm 1st hand that it works, I'll likely go for it.

Is the XS360 crank really 2+ lbs lighter?

I'd just prefer to keep the guinea pig engineering to a minimum on this build.
 
Yes the xs360 crank is lighter. From some reading on a lighter crank you will get up to rpm's a bit faster but you will loose stored energy. People that have done dyno testing on other motors with lightened cranks found little or no change to hp or torque. The xs360 carbs are pre-emission standard carbs and run much richer than any xs400 carb. I have run both and prefer the xs360's over the xs400's I run large uni foam filters and a free flow 2-1 exhaust on my 80 and run stock jets and settings with my xs360 carbs. You can find xs360 carbs from time to time but the hard parts to get is the metal support cover for the intake manifolds. The diaphragms that they use where only used in the 76-77 xs750 carbs and the xs360's no others will work:(
 
There are two straight looking xs360 cranks on ebay now for under $75. Seems a no brainer to shed over 2 + lbs of rotating engine mass that cheaply if ill be doing a full tear down anyway.

Are the xs400 carbs not capable of being jetted to run richer, equivalent to the xs360s?

The limited years of production, scarcity of parts, and lack of an aftermarket diapragm source in this age of ethanol infused gas causes me significant reluctance....Not sure Ill burn many calories to seek out a set of xs360 carbs.

Thanks for the insights.
 
Based on my readings on the subject a lightened crankshaft is only beneficial while the bike is already in motion and braking is not traction-limited (oval track racing).

A heavy crankshaft is desirable for launches like at the drag strip.

There are pros and cons to lightened crank shafts.
 
NA3S said:
There are two straight looking xs360 cranks on ebay now for under $75. Seems a no brainer to shed over 2 + lbs of rotating engine mass that cheaply if ill be doing a full tear down anyway.

Are the xs400 carbs not capable of being jetted to run richer, equivalent to the xs360s?

The limited years of production, scarcity of parts, and lack of an aftermarket diapragm source in this age of ethanol infused gas causes me significant reluctance....Not sure Ill burn many calories to seek out a set of xs360 carbs.

Thanks for the insights.
Click to expand...

Xs400 carbs can be jetted but will never run like the xs360 carbs. I know I tried:laugh: The xs360 carbs are setup more like the bs38's used on the mid 70's xs650's
 
have you tried beehive springs, they can run much higher revs.

you'll have to do your own research on fitment though
 
I spoke with an engineer at Kibblewhite last week and was quoted $600+, if they even had anything which could be adapted.
 
I agree with Chris the xs400 is just too limited on what mods can be done along with scarcity of aftermarket parts.Heres somethings I know of that can help push a a bit more horses out of the xs400 398 cc engine.
A 2 in 1 Mac system or home made similar type exhaust.
A free flowing exhaust with the unifilter pods.
Rejetting the mains up 2-3 sizes and 1 size up on the pilot.
Changing sprockets
Like you mentioned mild porting and polishing of the heads with maybe larger valves if you can find them.I would enlarge the intake and exhaust ports on the heads.Possibly shave a few thousands off the heads to raise compression.
Lighten your bike by removing anything unuseable on the frame.
Change carbs.
This wouldn't break the bank and all these mods would be fairly easy with the right tools.
Heres what I have read after these mods about 10mph faster but I don't know the torque value from a dyno.
 
I maybe wrong a bit off on the cc number its been a while since I read all about the specs on our bikes.
Also I believe I read about using banshee pistons as a alternate larger piston size for our bikes.:shrug:
 
Chris that Im not sure about 2 stroke but Im almost certain about reading the about using banshee pistons.It was the site where I read it and last year sometime.They started at 250 and went up as high as 500cc
 

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