Rebuild RZ350 - Go full stock or upgrade?

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kobra
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Rebuild RZ350 - Go full stock or upgrade?

#1 Post by kobra » Tue Oct 09, 2018 1:13 pm

I started tearing into my motor rebuild last night, simply doing an inventory of what needs to be replaced in order to get an idea of cost.

So far I am looking at a good number of things. All the engine seals, carb boots (engine and airbox sides), carb rebuild kits, (possibly the reed valves- do they go bad over time?), pistons, gaskets, etc. It is coming apart to the cases so I can paint it too. Thankfully the bottom end looks good still.

So I got to thinking... this is going to add up quick to several hundred dollars. I want to make it bulletproof mechanically, but am also on a budget. So a $1200 stroker crank is not an option. However if you were doing this, would you revert back to stock, or could I do some upgrades for about the same cost while I'm at it?

:smt023

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

#2 Post by nokturnal » Tue Oct 09, 2018 1:54 pm

if it were me, I would machine the head for squish, buy some TDR reeds, and invest in a couple nice carbs from the for sale section.

bullet proof and will be a great performer.
:smt017

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

#3 Post by kobra » Tue Oct 09, 2018 2:05 pm

Squish = compression ratio?

I actually have two sets of carbs that came with the bike. Was planning on just vapor blasting and then going with one of those K&L rebuild kits. Is there something better?

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

#4 Post by nokturnal » Tue Oct 09, 2018 2:14 pm

i am talking about the the PWK 28s
:smt017

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Re: Rebuild RZ350 - Go full stock or upgrade?

#5 Post by evan_calgary » Tue Oct 09, 2018 5:05 pm

This is good info.

Best to think of squish as a motor optimization rather than bumping compression like a 4-stroke. Lots of clearances in machining equals less than desirable compression chamber gap in most of the motorcycles. You are essentially blueprinting. It is free HP with little downside. Ultimately you are adding compression but not in the same terms as high comp 4-stroke pistons.

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Re: Rebuild RZ350 - Go full stock or upgrade?

#6 Post by Hooligan » Tue Oct 09, 2018 6:39 pm

Squish and reeds will make a nice difference.

Clean and rebuild the carbs as well.
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Re: Rebuild RZ350 - Go full stock or upgrade?

#7 Post by gpaddict » Tue Oct 09, 2018 7:07 pm

USE OEM CARB PARTS, or do it twice!
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Re: Rebuild RZ350 - Go full stock or upgrade?

#8 Post by graham heise » Wed Oct 10, 2018 7:09 am

Quote. ;;bottom end looks good still. looks are not measurments. I'd split the cases and hand the crank to a guy who rebuilds them and ask if everything is in spec. used parts can be reused if in spec and cleaned up. Are you going to rebuild it?
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Re: Rebuild RZ350 - Go full stock or upgrade?

#9 Post by RuZty » Wed Oct 10, 2018 10:24 am

Regardless of how you build it, use OEM parts where possible (seals, gaskets, bearings) and confirm used parts to factory specs. You also need to verify your work. If you cut the head (recommended) measure the squish when reassembled. Once the engine is back together pressure/vacuum test it for leaks or all your other efforts could be wasted. Plenty of info on here on how to do it. Check your power valves and bushings for wear, new seals won't last long on oval shaped parts and you'll have an oily mess on the front of your engine in no time. Spend the money now and be done with it.

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Re: Rebuild RZ350 - Go full stock or upgrade?

#10 Post by kobra » Wed Oct 10, 2018 12:53 pm

graham heise wrote:Quote. ;;bottom end looks good still. looks are not measurments. I'd split the cases and hand the crank to a guy who rebuilds them and ask if everything is in spec. used parts can be reused if in spec and cleaned up. Are you going to rebuild it?
What I meant by "looks good" is that it's still covered in oil, there's no corrosion, and it moves smoothly. I plan on splitting the cases to measure tolerances, replace the crank seals, and just give everything a check. I hope to not have to rebuild the crank if possible!
RuZty wrote:Regardless of how you build it, use OEM parts where possible (seals, gaskets, bearings) and confirm used parts to factory specs. You also need to verify your work. If you cut the head (recommended) measure the squish when reassembled. Once the engine is back together pressure/vacuum test it for leaks or all your other efforts could be wasted. Plenty of info on here on how to do it. Check your power valves and bushings for wear, new seals won't last long on oval shaped parts and you'll have an oily mess on the front of your engine in no time. Spend the money now and be done with it.
Good call. It would suck to try to save $50 and have to spend 8 hours tearing it all apart again!

The power valve bushings still look good. A tiny bit of wiggle but no obvious ovalizing. I have the service manual and plan to inspect everything as I go to ensure it's within spec.

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Re: Rebuild RZ350 - Go full stock or upgrade?

#11 Post by MK » Wed Oct 10, 2018 1:29 pm

Budget or perfect. Pick one.

I've been on a budget for looooong and was very creative in re-using things.
In the first place: Why did you disassemble it? If it aint broken, don't fix it.

How many km does the crank have and how many do you ride annually? If you have a 25000 km crank and do 3000 a year, it'll be good for another 10 years.

If the carbs have no issues, just clean them. Aftermarket rebuild kits suck and stock is expensive.

If the cylinder base or clutch cover gaskets aren't damaged: use silicone seal like Dirko (grey) and re-use 'em after cleaning.
I even re-used stock head gaskets with Dirko HT (red).

Most important point: Don't ride like you stole it. Constant long high rpm and load is poison for durability.
Bye
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Re: Rebuild RZ350 - Go full stock or upgrade?

#12 Post by kobra » Wed Oct 10, 2018 2:09 pm

MK wrote:Budget or perfect. Pick one.

I've been on a budget for looooong and was very creative in re-using things.
In the first place: Why did you disassemble it? If it aint broken, don't fix it.

How many km does the crank have and how many do you ride annually? If you have a 25000 km crank and do 3000 a year, it'll be good for another 10 years.

If the carbs have no issues, just clean them. Aftermarket rebuild kits suck and stock is expensive.

If the cylinder base or clutch cover gaskets aren't damaged: use silicone seal like Dirko (grey) and re-use 'em after cleaning.
I even re-used stock head gaskets with Dirko HT (red).

Most important point: Don't ride like you stole it. Constant long high rpm and load is poison for durability.
Something in the middle... I don't think perfect is a reality, but also don't want to skimp.

I actually don't know how many miles on it. The ODO says 20k miles but the spare ODO says 5k miles - not sure if it was used on another bike or not. I probably will ride it 1000 miles a year if that.

I ride everything like I stole it. :smt040

Basically when I got it, the heads were already off. One piston melted. The previous owner stuffed a t-shirt into the bottom end and it sat for 15 years.

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Re: Rebuild RZ350 - Go full stock or upgrade?

#13 Post by Questo vecchio rz » Wed Oct 10, 2018 9:52 pm

Okay you have some good advice above.

Here's my take on what you should do, The following is the (cheapest) way to your (fast & reliable RZ. I've been riding these things since 1984, and logged 100,000 miles between 3 RZs, I feel I know 1st hand in detail what works well if not best especially at this mild level of tune.

Not knowing your miles or if you have afternarket exhuast. These ARE IMPORTANT. There's really way too many variables and unknowns about what you have for a difinitive answer.
So this is what I'll recommend.

Obviously start with all new seals/gaskets. Check your power valve assembly..and pressure test your motor when your done....or if your paying a shop to do it...make sure they do it!

1.) Buy a $450.00 Hot Rods crank assembly (stock stroke)! It's the heart of your engine..if you want (bulletproof) a new crank has to be in your list. There are no $1200.00 cranks..only billet ones for Banshees cost that..you'd never ever need one.

2.) KEEP your STOCK carbs! You can jet to stock, and keep your airbox with aftermarket pipes or buy Toomey racings "perfect jet & filter kit), for even more performance. The stock 26mm carbs are F-ing damned good..and there FREE !

3.) Buy Toomey pipes..period. Others are good pipes too, but Toomey are your best (do everything pipe). If your on a budget and already have aftermarket pipes, just keep em... they will work fine..no worries.

4.) Have your head at least shaved/ milled, (make sure it has NOT already been done!) or send it to Scott @ SCR racing in Calif.
He's one of the best at setting up RZ/RD cylinder heads and the only guy I'll recommend on the W.Coast

4 .) Replace your front sprocket to a 16 tooth.

5.) Any $60.00 E-Bay RZ/Banshee clutch will work just fine, no need for a performance setup. You may prefer stiffer springs especially if your not riding it alot.

This is I feel the cheapest way to a strong engine on a budget. Yes you can check your existing crank if it specs out okay..you can use it, but obvioully longevity & peace if mind won't be what it would be with a new Hot Rods crank assembly.

A (full tilt ,top quality)stroker crank performance engine will cost you around $4000.00-$5000.00 dollars all said n done. So gauge your cost vs that figure.
Doing the work yourself, should be able to do this for around $1500.00 including pipes?

If your cranks good and your motor is airtight and everything to spec, you can beat on these things forever without a worry.
Last edited by Questo vecchio rz on Wed Oct 10, 2018 10:03 pm, edited 1 time in total.
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Re: Rebuild RZ350 - Go full stock or upgrade?

#14 Post by Evans Ward » Wed Oct 10, 2018 10:03 pm

^ my latest build is exactly like what Questo outlines with a difference at #1. I used a $450 new genuine Yamaha Banshee crank. Also helps to use a reputable RZ guru to do your boring and clearancing for pistons and ring gap. If your power valves are worn with excessive play, there are. billet ones at Fast From the Past that look and work exceptional. Not a giant HP build but very fun!
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Re: Rebuild RZ350 - Go full stock or upgrade?

#15 Post by JonW » Wed Oct 10, 2018 10:10 pm

Im with Evans, why buy a Hot Rods crank when an OEM is the same money? I think people forget about OEM as they just assume its too expensive.

I agree also that OEM carbs work fine, if you want to gain a few more bhp use a Zeel perhaps.

I also agree with MK, not doing 12000 revs will mean much longer engine life.
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