Source for XT350 piston

**xwhatsit** · 10th June 2008, 23:05

Hullo,

Where do we buy cheap Yamaha bits around here? An 86mm XT350 piston (rings, too, please) would be nice to have right now.

**Ixion** · 10th June 2008, 23:27

Which XT350 ? DOHC or SOHC?

**xwhatsit** · 11th June 2008, 00:26

Originally Posted by Ixion

Which XT350 ? DOHC or SOHC?

I couldn't tell you to be honest -- it has an 86mm bore, I believe circa 1983-85.

**pete376403** · 11th June 2008, 00:29

Have you tried Yamaha? I bought a piston for a FZR1000 recently (older, pre-EXUP model) $130 IIRC 13 days ex Japan. (no rings, pin or clips)
The only option was Wiseco, but would have meant buying a set of four at around $600-something.

**xwhatsit** · 11th June 2008, 00:36

`Tried Yamaha' -- do you mean go through a dealer? I've never spoken to one of them before. I've seen a few Wisecos on eBay, but they're expensive, and tend to be oversize or high compression.

Rather hoping there was an Econohonda/David Silver equivalent for Piano Bikes?

**Motu** · 11th June 2008, 18:00

How about a nice XT400 piston at 87mm.Take some photos and measurements.

**pete376403** · 11th June 2008, 19:31

Originally Posted by xerxesdaphat

`Tried Yamaha' -- do you mean go through a dealer?

Yup, that price was from Motomart in Lower Hutt

**Ixion** · 11th June 2008, 19:55

86mm is common size. Lots of bikes used it. G80 Matchless, B34, short stroke Manx Norton

86 x 86 gave a square 500cc.

If it's just an 86mm bore you need you could have a pretty wide choice.

**xwhatsit** · 12th June 2008, 00:11

I think the important bit is that it can bolt up to a CB250RS conrod without hassle, and clear the valves. Apparently the XT350 can fulfill that.

I believe, based on some basic googling, that it is the DOHC.

I would also assume that the TT350 would have the same basic sort of piston?

@Motu -- I'll try and track down some specs about the piston. Gudgeon pin, height etc. New sleeve at +12mm or +13mm; don't think it'll cause too many problems.

**Motu** · 12th June 2008, 21:20

The XT400 piston is 87mm - 20mm gudgeon and 27mm gudgeon height,and about 1mm dome.Looks nice - you wouldn't think I'd thrashed the ring out of it to look at it.I did weigh it once....oooh?....about that much.

**xwhatsit** · 14th June 2008, 02:21

CB250RS (and therefore presumably XT350? Trying to find specs on the piston but turned up SFA) uses a 19mm gudgeon pin, so no joy there.

Then again, just checked the crank I had in mind, and there does seem a tiny amount of radial play in the small end, at least when using the old gudgeon pin from a fecked piston. Except if going from small pin to big pin, you normally bush the piston, not bore out the small end, right?

**FilthyLuka** · 14th June 2008, 11:37

Wiseco XT350 Piston:

- 9:1 compression ration
- 86 x 59.6 (bore x stroke)
- Available in 1mm and 1.5mm oversizes aswell

Piston part no = 4674M08600
$172.82 USD per piston

Repl. Ring Set part no = 3386xc
Repl. Pin and Clips part no = S475

Grand total = $219.92 USD and you can order straight from wiseco

**xwhatsit** · 14th June 2008, 11:51

Problem is with the Wisecos, is that the piston crown tends to be pushed to the limits in order to raise compression ratios (although 9.1 is a mild increase). When you're sticking a different cylinder head on top, valves hitting worries me. Plus, I think I want slightly lower compression ratio as well, save the bottom end from too much pain.

Once I've worked out crankshaft situation, I'll call some of these Yamaha dealers.

**FilthyLuka** · 14th June 2008, 12:03

Originally Posted by xerxesdaphat

Problem is with the Wisecos, is that the piston crown tends to be pushed to the limits in order to raise compression ratios (although 9.1 is a mild increase). When you're sticking a different cylinder head on top, valves hitting worries me. Plus, I think I want slightly lower compression ratio as well, save the bottom end from too much pain.

Easy solution. Get two head gaskets and some goop. Put the two head gaskets together with goop inbetween em. Extra 5ft/lbs on the cylinder head bolts.

Worked on a cortina with a skimmed head...

**xwhatsit** · 14th June 2008, 12:19

Originally Posted by FilthyLuka

Easy solution. Get two head gaskets and some goop. Put the two head gaskets together with goop inbetween em. Extra 5ft/lbs on the cylinder head bolts.

Worked on a cortina with a skimmed head...

What I mean, is that putting an XT350 piston in a CB250RS motor is a marginal thing to begin with. The only reason I know it works is that it's been tried a couple of times and that it works. Fiddling with it by using a high-crowned high(er)-compression piston is fiddling with the magic formula to great success

Yep, I remember you posting up that double-head gasket trick; was just thinking last night that'd be a good solution to employ.