XS400 big bore

Bear Hands

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Hey guys, I know this topic has been covered before, but no-one mentioned what they did about the head gasket?
I found a company which makes custom head gaskets to order, I imagine probably expensive.
I also considered using annealed copper sheet and getting it water jetted or lasered, but again, its going to cost big time.
Any other ideas?

I have ordered a set of used XJR1300 rods (I had to buy all 4, so if anyone else wants to do the same, let me know and we can deal) with 18mm wrist pin.

I'm thinking:
GS500 pistons and liners (74mm) (think this may require the piston crown machining for valve pockets) these use 18mm wrist pin.

Stock liners bored to 72.5mm and GPZ900 pistons, but I know they need the crowns modifying a lot (4 valve piston) and that scares me a bit without a drawing showing exact details.

Stock liners bored to 72.5mm and GPZ1100 pistons, not sure if the crowns need machining but at least its a 2 valve piston. Not 100% on this, but some 1100s use 17mm and others 18mm pins, and to make it worse I *think* the 17mm pins are in 2 valve pistons and the 18mm pin are in 4 valve pistons...
 
i got the gpz900 pistons, but moved them on as they didn't suit my purpose.
I have the gs500 liners and the xjr rods. as I am (still) doing forced induction, i got honda pistons xlr250 I think to see how they work (their deck height is lower to lower the compression )

good luck in what you decide, my project had to take a long hiatus till other things get sorted first
 
See if Cometic will cut you a gasket..................also, even if 2 valve piston you have to watch the valve angle, which has been changing over the last few years to get flatter. Liners may be needed but if thick enough to remove too much stock from the aluminum cylinder casting then the cylinder will tend to leak and may even crack when torqued to spec. You may have to open up the case holes too. Or custom shorten the liners. Watch how deep the liner impinges on the cam chain tunnel too.
 
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It depends which route I take, if I go with the GS500 (74mm) pistons then I will need to machine both the liner OD and the barrels and case to take the larger liners, but this has been done before by others, I just hope I can convince the machine shop at work to sneak it in...

Regarding the valve pockets, I remember seeing a trick where a small piece of tool steel was brazed to the head of an old valve, then the engine loosely assembled. With the piston at TDC the valve was spun in the head with a hand drill and lightly pressed down to cut into the crown of the piston, creating the appropriate valve pocket.
Obviously this has to be done with great care to ensure the same amount of material is removed from each piston etc. But my concern is that I dont remove to much material from the crown and make it thinner/weaker, hence wanting to go with a 2 valve piston (which *may* not need anything at all).

I'm going to try and get the head gasket drawn up in CAD today and get some prices, if anyone else needs a big bore gasket let me know, I'm sure it gets exponentially cheaper per unit the more I order.
 
You take a measurement of the cutting tool height before cutting and then one after the cut and simply set a drill stop to let the other cylinder plunge cut the same amount.

If they change the valve angle even on 2 valve that easily may not work, your piston pocket will not be at the same angle as your valve and cut one side lopsided from the other. You as well need to know how thick the valve pocket material is, often different from the rest of the piston deck.
 
I'm going to try and get the head gasket drawn up in CAD today and get some prices, if anyone else needs a big bore gasket let me know, I'm sure it gets exponentially cheaper per unit the more I order.

put me down for one if your going to cad it :)
 
No worries Drewpy, had a feeling you might be in the market for one!
Are you running 75mm barrels tho?
Phoned a company in the UK today, they guessed at less than £100 each but said it would be cheaper if I did the CAD work, that’s in fibre with metal fibre rings.
 
No worries Drewpy, had a feeling you might be in the market for one!
Are you running 75mm barrels tho?
Phoned a company in the UK today, they guessed at less than £100 each but said it would be cheaper if I did the CAD work, that’s in fibre with metal fibre rings.
I'll have to check. Its been a while
 
Thanks for the video link Drewpy, I'm more inclined to save a few quid now and make my own copper gasket, anybody on here ever done it?
My only concern is how much torque is required on the head nuts, I'm thinking as the whole cylinder head surface needs to seal now, rather than mostly relying on the thin metallic inserts/fire rings (around the bore) in a conventional (much SOFTER) fibre gasket?
 
Thanks for the video link Drewpy, I'm more inclined to save a few quid now and make my own copper gasket, anybody on here ever done it?
My only concern is how much torque is required on the head nuts, I'm thinking as the whole cylinder head surface needs to seal now, rather than mostly relying on the thin metallic inserts/fire rings (around the bore) in a conventional (much SOFTER) fibre gasket?
when you anneal the copper, it softens it so it will seal. Make sure your barrel deck is smooth to give the gasket a chance to seal.
I would think standard torque settings as that is what the head studs will take before snapping.
I have Allan on my facebook friend list so could always ask him
 
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