Rebuild RZ350 - Go full stock or upgrade?

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kobra
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Re: Rebuild RZ350 - Go full stock or upgrade?

#16 Post by kobra » Thu Oct 11, 2018 12:03 am

WOW Thank you guys so for the detailed input.

Out of paranoia before dumping more time into it - I checked the crank tolerances tonight. According to my service manual, crank-side bearing play is spec'd at .010-.030" and mine fell at .022" and .023". Small end 'wiggle' is spec'd at .014-.039" and mine fell at .048" and .052"! It doesn't *feel* like too much wiggle, but apparently this is too much! Is that an assembly tolerance that is normal to open up, or is this thing trashed?

Is this the kit you're referring to, or should I just buy a crank and then get OEM seals separately?
http://www.hotrodsproducts.com/ProductI ... em_id=5655" onclick="window.open(this.href);return false;

Suddenly, it starts adding up...
$500 bottom end kit
$250 bore&hone both cylinders
$200 piston kits
$100 misc top end gaskets

:smt030

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kobra
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Re: Rebuild RZ350 - Go full stock or upgrade?

#17 Post by kobra » Thu Oct 11, 2018 1:43 am

Video of engine:
https://youtu.be/4vQ7prsUAtI" onclick="window.open(this.href);return false;

I feel zero perceptible radial play on both. Zero on the piston side either.

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Questo vecchio rz
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Re: Rebuild RZ350 - Go full stock or upgrade?

#18 Post by Questo vecchio rz » Thu Oct 11, 2018 2:57 pm

Yes that's the kit. Do that or the OEM Yamaha Banshee crank. Either will last you the life if your bike.

Do you have pipes?

Also I forgot to mention, add a set of reeds, TDR fiberglass reeds work pretty good. A low buck part that really helps.

You should rebuild the bottom end to be safe and secure.

You don't need anything wild or too expensive to make the RZ a quick lil toy.

Stay away from unnessesary upgrades like Aftermarket heads,O ringed stock heads, larger Mikuni or PWK, cylinder port work etc.. While they all work, you DONT need any if it.

(Pipes are mandatory though)....gotta have them. You'll gain anywhere from 5-13 h.p. just from pipes and your RZ should be about a mid 50 h.p. toy

Just go OEM as much as possible, add pipes, reeds, gearing and the head milling.. & your good to go.
At 1000 miles a year ...it will never fail you, no matter how hard you pound on it, as long as it's built to specs with req parts?

TDR is Tony Doukas Racing, he's a member here and can provide all your parts plus milling your head, I think you can get a forum member discount too.
You might also try any of the following, all are trusted and reliable friends of the RZ community.
Fast from the Past.
Economy Cycle.
Wicked ATV.
Spec 2.

With the above mods, you going to have a bike that's a smile a minute, lil wheelie Machine. You'll always be happy to go out and ride...it's just the nature of the bike. Small light and fun fun fun. They haven't made anything much like it since.
Last edited by Questo vecchio rz on Thu Oct 11, 2018 3:14 pm, edited 1 time in total.
Banshee (Baja) race bike,+ 2 A Arms,L.E.Ds, Toomey, +4 stroker IMS tank, run flats.
96 GSXR SRAD, Future Yoshimura rep.
85 custom Tri-Z
RZ/YZR bike(project)
86 VFR750 RC24 Merkel replica (project)
Royal Enfield Bullet 500

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Re: Rebuild RZ350 - Go full stock or upgrade?

#19 Post by brrrappp » Thu Oct 11, 2018 3:13 pm

kobra wrote:Video of engine:
https://youtu.be/4vQ7prsUAtI" onclick="window.open(this.href);return false;

I feel zero perceptible radial play on both. Zero on the piston side either.
Watching your video, it looks like there has been some contamination dirt/humidity/blow-by especially on the right side. I have a lot of dirt-bike experience and can say that when you do a budget rebuild of an engine that looks like that and skip the bottom end, it will cost you more the second time around! If the engine internals were exposed to humidity for extended time, it's pretty likely the bottom rod bearing will disintegrate in less than a season of riding. Plus if those little specs I see in your video are dirt, you'll never be sure that you got it all out by rinsing air-blasting etc.

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kobra
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Re: Rebuild RZ350 - Go full stock or upgrade?

#20 Post by kobra » Thu Oct 11, 2018 3:48 pm

Questo vecchio rz wrote:Yes that's the kit. Do that or the OEM Yamaha Banshee crank. Either will last you the life if your bike.

Do you have pipes?

Also I forgot to mention, add a set of reeds, TDR fiberglass reeds work pretty good. A low buck part that really helps.

You should rebuild the bottom end to be safe and secure.

You don't need anything wild or too expensive to make the RZ a quick lil toy.

Stay away from unnessesary upgrades like Aftermarket heads,O ringed stock heads, larger Mikuni or PWK, cylinder port work etc.. While they all work, you DONT need any if it.

(Pipes are mandatory though)....gotta have them. You'll gain anywhere from 5-13 h.p. just from pipes and your RZ should be about a mid 50 h.p. toy

Just go OEM as much as possible, add pipes, reeds, gearing and the head milling.. & your good to go.
At 1000 miles a year ...it will never fail you, no matter how hard you pound on it, as long as it's built to specs with req parts?

TDR is Tony Doukas Racing, he's a member here and can provide all your parts plus milling your head, I think you can get a forum member discount too.
You might also try any of the following, all are trusted and reliable friends of the RZ community.
Fast from the Past.
Economy Cycle.
Wicked ATV.
Spec 2.

With the above mods, you going to have a bike that's a smile a minute, lil wheelie Machine. You'll always be happy to go out and ride...it's just the nature of the bike. Small light and fun fun fun. They haven't made anything much like it since.
I have stock pipes that are rusted out - so I will need new ones.

Thanks for your input. I need to think this all over. See below
brrrappp wrote:
kobra wrote:Video of engine:
https://youtu.be/4vQ7prsUAtI" onclick="window.open(this.href);return false;

I feel zero perceptible radial play on both. Zero on the piston side either.
Watching your video, it looks like there has been some contamination dirt/humidity/blow-by especially on the right side. I have a lot of dirt-bike experience and can say that when you do a budget rebuild of an engine that looks like that and skip the bottom end, it will cost you more the second time around! If the engine internals were exposed to humidity for extended time, it's pretty likely the bottom rod bearing will disintegrate in less than a season of riding. Plus if those little specs I see in your video are dirt, you'll never be sure that you got it all out by rinsing air-blasting etc.
I am pretty sure the right side is the one that melted the piston. Then this engine has sat open for the last 15 years with nothing but a t-shirt covering the hole. Assuming the crank was physically okay, my plan was to remove it and thoroughly flush it of any debris. I was happy to find that the bearings are thoroughly bathed in oil with no corrosion, and it spins freely and smoothly.


Okay here's the million dollar question. Let's say I cheap out and run it with the bare minimum to get it running. In X amount of miles, the crank has worn and is starting to make noise. What are the consequences? Is it just a simple crank swap and labor to replace it, or am I liable to destroy something else? I am not entirely familiar with 2-stroke failure modes. It's clear that when people melt a top end they can just replace the top end - so does a bottom end failure also destroy the top end or is it isolated?

If you can't tell I'm still on the fence about cheaping out vs a full rebuild. It hurts me a little bit to put $900+ into the engine alone when it still won't be pristine (cause of the cracked case near the cs sprocket).

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Re: Rebuild RZ350 - Go full stock or upgrade?

#21 Post by brrrappp » Thu Oct 11, 2018 10:45 pm

How long will it last?
Well it's hard to know for sure. It is entirely possible the thing never blows up. But what I've seen and personally had happen is this:
The rod bearing disintegrates, spewing very hard metal bearing bits that get sucked into the cylinder and into the main bearings. With bore-able iron liner cylinders, it might only need a new crank, top-end, cylinder bore and some resurfacing of the combustion chamber. Gaskets, seals, your time etc.
You will feel it as a vibration and loss of power. I've had this happen on a YZ490. I actually drove the YZ490 about six miles home on trails with a trashed lower rod bearing! Of course, with a single cylinder, rebuilding a crank and top end is simple and relatively cheap. I think that little escapade cost me about $400 back in 1982. My friends CR125 lower rod bearing went and the rod broke at the crank-pin. The down-force momentum from the piston and broken rod punched right trough the bottom of the cases. He was done for the year.

Now, here's real expensive scenario: Let's say you're hammering the bike, showing your buddy what a two-stroke 350 can do, the rod bearing disintegrates, the rod itself breaks above the pin and the good side of your twin cylinder continues to run. Half of the broken rod, still connected to the crank and spinning at high RPM, driven like a circular saw by the good cylinder, literally cuts the cases in half! It takes less than 5 seconds. This I saw on a Yamaha Phazer snowmobile 488cc twin. Total loss. It damaged the cylinder, destroyed the upper and lower cases and obviously the crank was junk. There was chunks of metal everywhere! I wish now that I had pictures!
If the con-rod breaks around the bearing area in a twin and the engine is at high RPM, the crank pin will cycle around and punch something through the cases every time. Even at low rpm, if you are riding, the momentum of the engine being driven by the rolling wheels through the transmission will spin the crank until something breaks or you pull the clutch. Usually by the time you know it it is too late.

The bad news gets even worse for us street motorcycle riders as we are on two wheels and often in traffic or have a passenger. Imagine your bike seizing up or throwing a rod during a wheelie, a turn, or in traffic on the hi-way. There is way too much at stake to half-ass an engine rebuild..... In my opinion.
Last edited by brrrappp on Thu Oct 11, 2018 11:48 pm, edited 1 time in total.

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Re: Rebuild RZ350 - Go full stock or upgrade?

#22 Post by kobra » Thu Oct 11, 2018 11:40 pm

brrrappp wrote:How long will it last?
Well it's hard to know for sure. It is entirely possible the thing never blows up. But what I've seen and personally had happen is this:
The rod bearing disintegrates, spewing very hard metal bearing bits that get sucked into the cylinder and into the main bearings. With bore-able iron liner cylinders, it might only need a new crank, top-end, cylinder bore and some resurfacing of the combustion chamber. Gaskets, seals, your time etc.
You will feel it as a vibration and loss of power. I've had this happen on a YZ490. I actually drove the YZ490 about six miles home on trails with a trashed lower rod bearing! Of course, with a single cylinder, rebuilding a crank and top end is simple and relatively cheap. I think that little escapade cost me about $400 back in 1982. My friends CR125 lower rod bearing went and the rod broke at the crank-pin. The down-force momentum from the piston and broken rod punched right trough the bottom of the cases. He was done for the year.

Now, here's real expensive scenario: Let's say you're hammering the bike, showing your buddy what a two-stroke 350 can do, the rod bearing disintegrates, the rod itself breaks above the pin and the good side of your twin cylinder continues to run. Half of the broken rod, still connected to the crank and spinning at high RPM, driven like a circular saw by the good cylinder, literally cuts the cases in half! It takes less than 5 seconds. This I saw on a Yamaha Phazer snowmobile 488cc twin. Total loss. It damaged the cylinder, destroyed the upper and lower cases and obviously the crank was junk. There was chunks of metal everywhere! I wish now that I had pictures!

The bad news gets even worse for us street motorcycle riders as we are on two wheels and often in traffic or have a passenger. Imagine your bike seizing up or throwing a rod during a wheelie, a turn, or in traffic on the hi-way. There is way too much at stake to half-ass an engine rebuild..... In my opinion.
Yikes!!!! And I thought my Kawasaki Concours 1000 gave me nightmares... (hydrolock)

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Re: Rebuild RZ350 - Go full stock or upgrade?

#23 Post by kobra » Mon Oct 15, 2018 11:52 pm

I've been reading up on setting the squish. From what I've learned, too little squish (stock) can't hurt, it just isn't optimal for power. Too much squish can lead to detonation. I had no idea it played such a big role in fuel mixing, the more you know!

I have read about some people simply peeling a layer or two off the stock multi-layer head gasket to achieve the correct squish values. Is that... normal, or frowned upon?

Regarding my rebuild - I am going to bring my engine to a reputable engine repair shop nearby who will be boring/honing the cylinders, to get a professional input on it. There are some things that are just based on feel and I quite grasp through the internet! Regarding the connecting rod wiggle, it is actually still within spec. Upon further research, the install spec is .014-.039" with a service limit of .080" (this value was not in my service manual, but instead in the Banshee manual).

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Re: Rebuild RZ350 - Go full stock or upgrade?

#24 Post by JanBros » Tue Oct 16, 2018 3:27 pm

kobra wrote:I've been reading up on setting the squish. From what I've learned, too little squish (stock) can't hurt, it just isn't optimal for power. Too much squish can lead to detonation. I had no idea it played such a big role in fuel mixing, the more you know!
squish has 2 main properties : the gap and the area.
a stock engine certainly does not have a too little squish gap, so I suppose you are talking about the area ? but area alone means little without the gap. too big gap can lead to deto.
if it runs, you can race it !

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Re: Rebuild RZ350 - Go full stock or upgrade?

#25 Post by kobra » Fri Oct 19, 2018 11:19 pm

Just wanted to share some info. I dropped off the cylinders to get reworked today. The shop is run by a seasoned engine builder who used to work at a Yamaha race shop and worked on RZ's and TZ's back in the day.

He checked my crank and noted it looked quite good. Everything is still tight and smooth. He recommended opening the webs to the maximum tolerance to help with oiling, and welding the crank if the bike will be hopped up or tracked. Since I plan to keep it stock and it hadn't walked at all I decided to leave it as-is.

We were trying to figure out why the piston fragmented in the first place. There is evidence that it was run for a little while before it finally stopped, as there is excessive black soot around the side of the piston. It's possible that the exhaust pipe was clogged or plugged up - which is plausible since this CA version has 3 catalytic converters. Or possibly it sucked transmission oil into the combustion area. He recommended running premix the first tank to be absolutely sure the oil delivery system is working, then switching over.

I decided to go with Wiseco's using the next available size up (still at stock 64mm bore, so whatever it takes to clean up the damaged side). It will take a bit of removal to clean up the one cylinder since it has some notable grooves. I've read a lot of mixed results on the Wiseco's online and researched it thoroughly. Theoretically a forged piston will be better in every way - stronger, tougher, lighter. According to my research if you bore the cylinder to the correct piston clearance spec it will work fine - it's when people put new pistons in an old worn out bore that they can have issues - either excessive play, or too tight tolerance.

I do tend to ride my bikes hard, so I am wary of doing any upgrades that will sacrifice longevity. I would rather have a slightly slower build that I can ride normally than a more powerful build that is more delicate, if that makes any sense!

Anyway, just thought I'd share that info! I could tell this guy was a wizard when it comes to these bikes. He accurately guessed the axial rod play within .001" just by feel. So I am comfortable with him doing the work.

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Re: Rebuild RZ350 - Go full stock or upgrade?

#26 Post by Questo vecchio rz » Sat Oct 20, 2018 11:27 pm

Jeeeez fixed all my Typos.. lol

For your purpose, and situation.thats good news, so just go with it.
The basic RZ mods I gave you are all you need to have a reliable quick RZ.

Do them all, FYI while desireable you don't have to go all technical about your head w squish etc.. you can get by just fine with a mild milling, The engine will run cooler w better compression as well. Spec 2 used to just fine this back in the early days. (Don't! Quote me in this) but I think it was 20 thousands. (Don't do it until you determine what you got 1st.)
Aside from pipes... this is all LOW buck!
You don't even have to rejet your carbs...just for now drop use in UNI filter w stock jetting. You'll have a (fresh top end, Reeds, smaller front sprocket, and hopefully pipes.
Check here for anyone with used pipes, any brand will work, even stock Canadien pipes are good performers..but they weight a ton. Look at DGs there often under $400.00.
Pipes are mandatory for good performance.
You'll have a fairly solid bike w/o stressing your engine. At 1000 miles a year you should get your dollars worth.
Good luck. Hopefully someone here has some pipes they can kick down your way!
Last edited by Questo vecchio rz on Sun Oct 21, 2018 11:34 am, edited 1 time in total.
Banshee (Baja) race bike,+ 2 A Arms,L.E.Ds, Toomey, +4 stroker IMS tank, run flats.
96 GSXR SRAD, Future Yoshimura rep.
85 custom Tri-Z
RZ/YZR bike(project)
86 VFR750 RC24 Merkel replica (project)
Royal Enfield Bullet 500

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Re: Rebuild RZ350 - Go full stock or upgrade?

#27 Post by kobra » Sun Oct 21, 2018 12:40 am

Definitely looking for pipes still. Toomey's and Wicked Racing seem like the BEST but they're $750-800...

I found the DG's on eBay for about half that. Are they any good, or will the RZ purists point and laugh at me for running them? Anything without catalysts and that lets it breathe, adding some ponies will be nice :). Also I would hope they fit well.

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Re: Rebuild RZ350 - Go full stock or upgrade?

#28 Post by JackB » Sun Oct 21, 2018 10:27 am

I have used wicked pipes,they did not look pretty but they ran and performed good. The original RZ I had had Toomeys on it and they ran good too. I have Jim lomas now,The performance does not seem to be all that but they sure look great. I have DGs on another bike with a RZ engine. I would say if your on a budget they may be the way to go for you. They are probably the cheapest you will find,and the performance is comparable every way to the others. The dyno might say something different but on the street they are fine. Like the wicked pipes the DGs are not the best looking. The overall look is similar to the others but the welds can bee sloppy looking.
1984 Rz350, Wicked Toomey rep pipes, Dynojet kit,Zeel unit,Toomey Y boot filter.

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Re: Rebuild RZ350 - Go full stock or upgrade?

#29 Post by Questo vecchio rz » Sun Oct 21, 2018 11:39 am

What he said above... DGs perform just fine. Not the best looking, but deliver the performance. Stick with them for now, unless a forum member can help you out with another brand.
FYI I've used about 6 different pipe designs. They ALL work, Toomeys are what your after but anything is good. So you'll be fine whatever your budget!
Banshee (Baja) race bike,+ 2 A Arms,L.E.Ds, Toomey, +4 stroker IMS tank, run flats.
96 GSXR SRAD, Future Yoshimura rep.
85 custom Tri-Z
RZ/YZR bike(project)
86 VFR750 RC24 Merkel replica (project)
Royal Enfield Bullet 500

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Re: Rebuild RZ350 - Go full stock or upgrade?

#30 Post by brrrappp » Sun Oct 21, 2018 12:28 pm

I don't have any ride time on the DG pipe but I would agree with Questo.
I have 3 US RZ350's. One with Toomey pipes, 1 with Factory Products and one with Spec 2.
The Toomey has a better sound, feels stronger in the mid RPM range, and has the best looking stinger.
The Spec 2 seems to Rev higher before they flatten out.
The Factory Products and the Spec 2 feel about the same at lower RPM.
Of these 3 pipes, my personal opinion is that the Toomey is the one to have if you are doing a restore for "Show" as well as GO."
The seat of the pants "GO" part is very close between these 3 pipes.


I'd buy whatever you can find on the cheap for starters and continue to look for what you really want over time. You can always sell RZ350 pipes on eBay and recover most, if not all, of your initial investment.

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