Operation: RZ350N REVIVAL - Florida 1985 48H Project

[kobra]

Nice job. Amazing how bad those scratches on the piston look, only to realize they are cosmetic and have zero effect on the function.

[TwoStrokeNut]

Thanks. I have often wondered if shirt scratches had any affect on anything, but assumed that they did not. I know you normally do a lot of research on topics, so its good to hear another indication that it doesn't.

[TwoStrokeNut]

Service M35 - Compression and Leak-down Tests (Again!)...

The first test I did was a compression test. Even with the cylinders lightly oiled, I only reached 90psi on each cylinder. I was hoping for more, but maybe the rough surface of the new rings were contributing to that low number. At least it is up from the 80psi recorded earlier with the old rings. I will give it another go after the rings have a chance to break in and smooth out a bit.

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Next was a leak-down test. Having all the parts handy from the last time, it was a piece of cake. The lead hose from my compression tester attached to one spark plug hole. I am able to check vacuum and pressure with this setup.

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And here are the leak-down numbers.

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These numbers very closely matched those from last time. I also squirted a dishsoap solution all over the leak point to check for blowing bubbles… nothing. So I’m calling it good and will be getting on with the rest of the re-assembly.

M35 Total Cost: US$0.00 (Nothing needed)

[silverstrom]

Have you done the compression test with a different gauge?

[TwoStrokeNut]

Have you done the compression test with a different gauge?

I do not have another compression tester to verify readings. But if you recall, I earlier compared the compression tester gauge to another gauge (and my regulated air gauge) by hooking them directly to my shop air compressor and readings seem to be fairly accurate.

I guess there is still a chance of a leak in my quick disconnect fitting, and that could explain low readings here and some/all of loss in the leak-down test.

Maybe its time to invest in a good compression tester.

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[TwoStrokeNut]

Service M36 - Install new clutch springs...

Since the transmission had already been flushed with new oil after the cases were split and the new Motul oil only had 13 miles on it, I decided to capture and recycle it during this drain and refill. I feel pretty confident I didn’t introduce any extra dirt in it while draining.

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I wanted to get some hard measurement on the improvement, so I rigged up a way to measure clutch lever pull lever using my luggage scale.

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Enough though they were new springs, I wanted to measure them.

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I’m not sure it’s necessary, but I thought it would be a good idea to pair up matching lengths and install them across from each other for best balancing of force.

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They all are at the upper end of the range.

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Without disturbing the oil supply and pressure lines, I was able to carefully swing the clutch cover out of the way long enough to swap out the springs. Coolant was already drained during the piston ring swap.

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A closer look.

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I replaced the springs in pairs and found leaving the new ones about .25” from seated to signify which ones had already been replaced. Once all six new springs were installed, I tightened them up.

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Time for a final lever pull test and I got 5.26 pounds this time. An increase from 4.50 pounds to 5.26 doesn’t seem like much, but it represents a 17% increase, and hopefully enough to keep it from slipping during that 3 to 4th gear full power upshift.

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M36 Total Cost: US$38.46 (Clutch springs)

[JonW]

Good work. Most clutch slipping problems stem from weak springs. If you measure the plates you will often find them to be fine. i measured all the plates Id saved, had come out of engines i bought and ones i got with purchases in boxes of bits - quite a lot of full clutch packs, ie 10+. And.... {drumroll}... 90% of them were fine, but all the springs (yes ALL) were useless.

[Redline Junkie]

Great section on the clutch! I need to pull mine apart too, as I get some slippage under WOT sometimes. I have a new set of EBC springs in the shop I might install. I will be checking my pull force too before and after!

[TwoStrokeNut]

Good work. Most clutch slipping problems stem from weak springs. If you measure the plates you will often find them to be fine. i measured all the plates Id saved, had come out of engines i bought and ones i got with purchases in boxes of bits - quite a lot of full clutch packs, ie 10+. And.... {drumroll}... 90% of them were fine, but all the springs (yes ALL) were useless.

Thanks. My observation agrees with yours... My original plates measured on the high side for thickness but the springs were on the low side. I believe you suggested replacing the springs last time I had it apart, but I didn't have any on hand at the time and I was anxious to get the engine back together. So the old ones went back in, unfortunately, and proved to be weak.

In the back of my mind, I knew this engine was coming back apart, and here I am, see the inside of this engine again for some upgrades. Luckily, it is proving to be a very simple job that didn't cost any more than the spring cost now, so no harm done. Even the clutch cover gasket was reusable.

Thanks for you continued and informative input!

[TwoStrokeNut]

Great section on the clutch! I need to pull mine apart too, as I get some slippage under WOT sometimes. I have a new set of EBC springs in the shop I might install. I will be checking my pull force too before and after!

You probably have a similar situation to what I had... A hint of slippage at WOT. I have not reported it here yet officially, but the new OEM springs seemed to have solved my slippage issue completely. Don't quote me on it, but I seem to recall that EBC springs are a bit stiffer than OEM, and if so, that would help even more. Good luck to you. I would be interested to see what pull force you record. Thanks for chiming in.

[kobra]

I found that I wouldn't have slippage with the stock springs, but if I put so much as 1/4lb pressure on the clutch lever,it would slip. I installed 3 heavy duty springs (from Tusk) and 3 stock springs. Clutch pull feels about the same, and it's no longer on the edge of friction.

[TwoStrokeNut]

I found that I wouldn't have slippage with the stock springs, but if I put so much as 1/4lb pressure on the clutch lever,it would slip. I installed 3 heavy duty springs (from Tusk) and 3 stock springs. Clutch pull feels about the same, and it's no longer on the edge of friction.

I think this is a great approach to the issue. Although I believe my full power slippage problem is gone with the new OEM springs, I agree that even a strong headwind pushing on that lever can start disengaging the clutch (okay, I'm exaggerating a little, actually maybe a lot), but I do know what you mean. The lever pull on this bike is really light so I wouldn't mind it being stronger to closer match my other bikes.

Since I plan to keep the bike for a long time, and knowing springs lose their spring over time, I'm sure I will be re-visiting this issue again someday.

[TwoStrokeNut]

Service M37 - Install larger main jets (Mikuni VM4/042/260)...

Before the carbs went back on, I wanted to increase the main jet size just a bit. It has always ran fine with the 240’s in, but I have been warned about running lean with aftermarket chambers.

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So 260’s went in.

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Are 260’s still too small? Maybe, I don’t know… I’m no tuner. I will order some 280’s for the next time the carbs come off and we will see.

M37 Total Cost: US$15.90 (Main jets)

[TwoStrokeNut]

Service M38 - Install cooler spark plugs (NGK BR9ES)...

After reading about Kobra’s misfortunes on his newly rebuilt engine (still sorry to hear about that), I decided to go back to a cooler spark plug. This and slightly larger main jets should cool combustion temps down somewhat, I would hope.

Here are the BR8ES’s that came out. I am holding them respective to the side they came out of with the bike behind them. Again, I’m not a tuner, but it appears the right side cylinder has been running rich. Even when I pulled the bike out of storage and looked in the exhaust ports, I remember the right side having more carbon build-up. Is there any explanation for this?

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BR9ES’s are going in.

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I don’t remember the 9’s ever giving me any issues in the past, and I used to ride it quite a bit in the early 2000’s.

M38 Total Cost: US$5.84 (Plugs)

[TwoStrokeNut]

Service M39 - Replace coolant...

Since I hope to not tear this engine apart again for a while, it’s time to put the final coolant in. I don’t know if there is a huge difference in coolants, but I chose Maxima Coolanol because it is readily available, is an ethylene based glycol, safe for aluminum and magnesium, and the other characteristics sound pretty good. I know I’m paying extra for the premix 50/50 blend, but these bikes don’t use much of it anyway. I always mix my own for the cars that take 3 and 4 gallons though.

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M39 Total Cost: US$8.00 (Coolant)