New piston for 1985 Yamaha SRX600?

[bacon]

Hi Guys,

I'm looking at ordering a new piston and rings set for my 1985 Yamaha srx 600 engine and I'm wondering if I have this correct. Now before I am nailed to a cross for abusing this engine, this is how I brought it (hopefully my imaged was attached ok). Just to be sure, I need to order a 95.50mm piston right? I'm assuming this because of the 50 printed on the top of the piston (hopefully meaning .50 oversize). Probably a really stupid question, but I'm not too keen on ordering a piston only to find to find I need to bore it out to fit, or worse still to order one and find it's too small in which case I will straight up cry.

Any help is greatly appreciated.
Cheers,
Chris

http://i.imgur.com/bC03KkP.jpg?1
http://i.imgur.com/RZZ1xk8.jpg?1

[SS90]

It's easy to tell. If you can get hold of a set of Verniers, simply measure the bore, even if it is worn, Verniers are accurate enough to tell if they are oversize, or original bore (over sizes are generally in .25 increments)

[Grumph]

Yes, that's a .50mm oversize piston...but no, that may not be what you order.

Looking at the skirt of your piston, the bore is going to need a hone as an absolute minimum.

Take it to a pro engine recon shop and get them to measure the bore as it stands. Tell them the standard bore clearance figure - get that either from a manual or the internet - and they'll tell you if it will have to be bored or if you'll get away with a hone.

Edit - on the last SRX I did 50 on the piston was indeed .50 oversize...

[AllanB]

Just get a big bore kit. Oh yeah :yes:

[Grumph]

Just get a big bore kit. Oh yeah :yes:

Ha - pretty well all the SRX 600's in NZ are kick start....I did a hot one for a very large gentleman who could leave it unattended with key in, in the certain knowledge no one could start it....He's still a friend and i call on him when i want a Z1 or GS Suzuki motor lifted and moved...

[bacon]

Yes, that's a .50mm oversize piston...but no, that may not be what you order.

Looking at the skirt of your piston, the bore is going to need a hone as an absolute minimum.

Take it to a pro engine recon shop and get them to measure the bore as it stands. Tell them the standard bore clearance figure - get that either from a manual or the internet - and they'll tell you if it will have to be bored or if you'll get away with a hone.

Edit - on the last SRX I did 50 on the piston was indeed .50 oversize...

Thanks for the info, I'm a little on the broke ass nigga side of things so getting the pros in and having a rebore might break my bank a little. The cylinder isn't too bad, I think a hone will clean it up nicely. By the looks of things I suspect the old owner had it rebored and new piston installed, then probably thrashed it during its run in time. I've been looking on ebay for cheap piston kits with the 0.5 oversize. Was thinking about this:

http://www.ebay.com/itm/390270044972?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I have a bad feeling those are made in China though.

This would definitely be made in China but is so cheap and therefore tempting:

http://www.ebay.com/itm/Piston-Kit-with-Pin-Rings-Clip-Set-For-YAMAHA-XT600-0-5mm-Oversize-Bore-95-5mm-/171268837760?pt=Motorcycles_Parts_Accessories&hash=item27e06b1180&vxp=mtr

[bacon]

Just get a big bore kit. Oh yeah :yes:

That would be pretty dam cool if I had the bank. What can you get them to? 640?

[Grumph]

Thanks for the info, I'm a little on the broke ass nigga side of things so getting the pros in and having a rebore might break my bank a little. The cylinder isn't too bad, I think a hone will clean it up nicely. By the looks of things I suspect the old owner had it rebored and new piston installed, then probably thrashed it during its run in time. I've been looking on ebay for cheap piston kits with the 0.5 oversize. Was thinking about this:

http://www.ebay.com/itm/390270044972?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I have a bad feeling those are made in China though.

This would definitely be made in China but is so cheap and therefore tempting:

http://www.ebay.com/itm/Piston-Kit-with-Pin-Rings-Clip-Set-For-YAMAHA-XT600-0-5mm-Oversize-Bore-95-5mm-/171268837760?pt=Motorcycles_Parts_Accessories&hash=item27e06b1180&vxp=mtr

Namura seem quite good but the choice is yours....i would do as SS90 suggests and confirm bore size by measuring prior to ordering.
Most pro shops will measure free of charge if you don't have the gear.

[HenryDorsetCase]

Thanks for the info, I'm a little on the broke ass nigga side of things so getting the pros in and having a rebore might break my bank a little. The cylinder isn't too bad, I think a hone will clean it up nicely. By the looks of things I suspect the old owner had it rebored and new piston installed, then probably thrashed it during its run in time. I've been looking on ebay for cheap piston kits with the 0.5 oversize. Was thinking about this:

http://www.ebay.com/itm/390270044972?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I have a bad feeling those are made in China though.

This would definitely be made in China but is so cheap and therefore tempting:

http://www.ebay.com/itm/Piston-Kit-with-Pin-Rings-Clip-Set-For-YAMAHA-XT600-0-5mm-Oversize-Bore-95-5mm-/171268837760?pt=Motorcycles_Parts_Accessories&hash=item27e06b1180&vxp=mtr

If you look up the definition of "false economy" on the internet, that post comes up. If I have learned anything pissing about with stuff it is that it is a sure way to make a grown man cry is to half arse something (Nah, man CBF actually checking and KNOWING I'd rather just apply credit card and hope for the best). Seriously, do it properly. Measure it then order the correct bits.

I used to own an SRX: great little bike. Not that bad to kickstart even for my pissy arse weak little legs. they have a decompression system. Would start from hot first kick, from cold second kick. Woe betide you if you rode it for like 5 mins then turned it off. cue 20 minutes of kicking.

[SS90]

I used a Namura piston in a DRZ400 last year, purely because they came in a larger oversize than OEM (this had seen a few miles), never had a problem with it, but it was only one. Certainly felt and looked top quality to me.

[mr bucketracer]

I used a Namura piston in a DRZ400 last year, purely because they came in a larger oversize than OEM (this had seen a few miles), never had a problem with it, but it was only one. Certainly felt and looked top quality to me.i think the bucket boys are missing you

[bucketracer]

............ :killingme

[TZ350]

Thanks for the info, I'm a little on the broke ass nigga side of things

The piston has probably collapsed a bit from being squeezed in the bore, otherwise it does not look to bad, so if your really keen on saving a dollar. And there are no cracks in the piston that you can see and the bore cleans up with a hone and the rings are not to bad then have the piston lightly knurled on the thrust faces by an engineering shop.

This and micro peaning is an old trick to expand pistons, and don't worry if its a bit tight afterwards, it will soon adjust itself. This little trick worked a treat back in the day of engine reconditioning shops and real tradesmen who could make a new piston from a blank or tickle up an old one when things were desperate. It is something that you could try yourself if you want to, to get your ride going again without spending many $$$$ at all.

Then again if your wanting to be really cheap, after cleaning the piston up, heat it until its smoking hot, then gently squeeze it in a vice across the pin bosses, to much and it will crack, just enough and it will be a snug fit in the bore again.

[F5 Dave]

Which considering it will be doing a lot more revs than a 60s car in a vibrating single. . . Expect to be walking home.

If the Namura(sp) piston has worked ok for others that would seem the best option. Trying to find a new barrel if the $70 'you have no regrets' version goes putt would be more expensive and they've been used up by singles racers so harder to find I'd think.

$200 landed plus a bore, say $80. And whatever gaskets cost, Suck it up.


but more importantly - why did this happen? Probably has a tiny driven oil pump which may have failed or stripped plastic cog. Guess should be possible to test with a battery drill, but I'm not up on 4 stroke stuff.

[TZ350]

If the Namura(sp) piston has worked ok for others that would seem the best option. $200 landed plus a bore, say $80. And whatever gaskets cost, Suck it up.

but more importantly - why did this happen? Probably has a tiny driven oil pump which may have failed or stripped plastic cog. Guess should be possible to test with a battery drill.

Good advice.


Which considering it will be doing a lot more revs than a 60s car in a vibrating single. . . Expect to be walking home.


Good advice to. if you are in the habit of letting fear hold you back from success.

You're not working with a 60's piston and the techniques of metal forming are as relevant today as they have always been. Think it through for yourself and don't let other people limit your ambition.

[F5 Dave]

Shout yourself an apostrophe and an 'e' when spelling 'you're'

[husaberg]

i think the bucket boys are missing you

http://media-cache-ec0.pinimg.com/236x/2d/e6/3b/2de63b3b3604bbd8152cf7b6930231bd.jpg

[Paul in NZ]

I looked at SRX 600's a lot at one point and I still think there is one in my future - not sure why...

Making them bigger than they are seems to be not recommended. In fact increasing the power output full stop seems to a little fraught unless you are spending big big dollars to beef everything up. Of course this is not actual experience...

[HenryDorsetCase]

If you get one hang out for the slightly later version. Same engine and very similar chassis and styling but has three spoke wheels, rear monoshock and a way better front brake only a single disc but larger rotor and 4 piston caliper. also 17 inch wheels when the earlier one had 18's. Lot of fun particularly on a twisty road.

[Grumph]

I looked at SRX 600's a lot at one point and I still think there is one in my future - not sure why...

Making them bigger than they are seems to be not recommended. In fact increasing the power output full stop seems to a little fraught unless you are spending big big dollars to beef everything up. Of course this is not actual experience...

Not really...The rod and pin will take anything you throw at them. Forged piston isn't really needed unless you're racing it. The heads respond to porting very well indeed on stock valve sizes. Cam profiles as std are very mild so not much more cam gives a big boost..Carbs must be changed - the OE part slide part CV setup is so hard to retune it's not funny. decent pipe helps too.

Biggest problem - if you'd call it that - is that while it's apart, you'll logically look at the gearbox too. Because most of them have spent their lives in town at low speeds, 2nd and sometimes 3rd gear will be through the hardening. Top can be the same too. It's the "big single" effect - bang, pause,bang, oscillating low frequency loadings on the most used gears. Can get costly....

[HenryDorsetCase]

Not really...The rod and pin will take anything you throw at them. Forged piston isn't really needed unless you're racing it. The heads respond to porting very well indeed on stock valve sizes. Cam profiles as std are very mild so not much more cam gives a big boost..Carbs must be changed - the OE part slide part CV setup is so hard to retune it's not funny. decent pipe helps too.

Biggest problem - if you'd call it that - is that while it's apart, you'll logically look at the gearbox too. Because most of them have spent their lives in town at low speeds, 2nd and sometimes 3rd gear will be through the hardening. Top can be the same too. It's the "big single" effect - bang, pause,bang, oscillating low frequency loadings on the most used gears. Can get costly....

replacements available or is it a call to Mike Jones and a cubic foot of $10 bills later?

[Grumph]

replacements available or is it a call to Mike Jones and a cubic foot of $10 bills later?

If it was the dogs it would be Mike...but it's always the teeth going through the hardening. Last time i asked , they were available.

[RDjase]

If you get one hang out for the slightly later version. Same engine and very similar chassis and styling but has three spoke wheels, rear monoshock and a way better front brake only a single disc but larger rotor and 4 piston caliper. also 17 inch wheels when the earlier one had 18's. Lot of fun particularly on a twisty road.

There is a later model twin SRX400 with three spoke mags, 320 rotor and 4 pot caliper, 17 front but 18 rear. Sport demons or BT45'swork well on them so the 18inch wheel isn't a problem anyway. The first model had wheels and brakes like RZ350. The bikes were the same apart from the wheels

The later single shock bike was heaps different, and electric start I think

http://www.srx400.co.uk/

http://www.srx600.net/

The front sprocket is different on the 400 to 600, fine spline and course spline, cant remember what has what. Maybe different gearbox internals?

[bacon]

Hi again guys,

Sorry for the super slow reply, I hope my old dead threads aren't clogging up the place(sorry if they are, I can delete one maybe?). I've decided to take the majority advice and spend a few extra $$
I currently emailing around engine restorers trying to find someone who can do me a rebore and a camshaft recondition (without charging an arm and a leg). If you know anyone who fits that description and is in Auckland, I'd like to know. Once I've got that sorted I was thinking of:

Wiseco 1mm oversized, 11.5:1 compression piston kit $180..or so (is 95 octane high enough?)
Maybe having the lobes enlarged on my cam making it hot? (I'm really no expert on cam tinkering, I'll let the engine reconditioner tell me what I can do)
If I'm going be cam tinkering I guess I'll need to find some custom valve springs ( Hopefully a good reconditioner can help me out there)
full gasket set
Also have a 2 into 1 carb manifold and a 38mm mikuni flatside ready to go ( Will
will need a 2 into 1 exhaust collector section made up so I can fit a supertrapp I have lying around (anybody know someone who can do that for cheap?)

I also have some pretty good nick srx400 engines and some xt400 stuff around. So I'll canabalize whatever fits.

I figure, if I'm going to spend a few hundred getting it running, why not a couple hundred more and try squeeze 50 ponies out of the old girl. Hugely grateful for your advice guys, I'd buy you all a beer if we were at the pub.....and I wasn't a peasant

[ducatilover]

11.5:1? I personally wouldn't bother with that on a road going single you'll never pull the revs to justify it, nor will the engine flow enough to justify it either.
Does it have an electric start? It may not like it, and you'll need some mighty legs if you haven't got a de-comp on the kick.
Hard to say if 95 will be enough without experiencing myself how good the knock resistance is on one of those :crazy:

[Grumph]

If the squish is set correctly, the knock resistance is quite good - but yeah, that's too much com for road use. If you've committed to the piston buy, I'd drop com by laying back the chamber walls around the valves. 10 : 1 for road use on pump fuel would be max as they don't have a lot of finning....maybe an oil cooler too.