RZ/RD 350 & Misc. 2-Stroke Tech BBS

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 Post subject: Blowing oil on new motor
PostPosted: Sun Sep 23, 2018 8:37 pm 
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Location: OKC & AUSTX
421 stroker, 30 miles total. 1988 F2.

Clearly it's blowing oil/premix. The left chamber is loose. The mechanic made a shim to snug the chamber up, ( when I bought it, it had two crush gaskets and at tube of RTV, the shim was to resolve this).

I assume the mess is from the loose chamber? Right?

Thanks!ImageImage

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PostPosted: Mon Sep 24, 2018 12:57 pm 
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Might be your power valve seals,


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PostPosted: Mon Sep 24, 2018 6:53 pm 
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Good point. Thank you.

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PostPosted: Mon Sep 24, 2018 7:25 pm 
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wow, did you reline the bores to get to 421 with the OEM cyls? Or was that a typo and its a OEM +4 and about 375 or so?

I'd also look at the PV seals/bushes, but seal the pipes up with sealant while youre there as well. The only way to tell is to take the fairings off and look and where its coming from.

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PostPosted: Tue Sep 25, 2018 5:05 pm 
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No, the mechanic said there is plenty of wall.

Note I just wanted to go the next size over, I pick the motor up and it's now huge...

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PostPosted: Tue Sep 25, 2018 5:40 pm 
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421 on stock barrels? not unless you went +8 crank and trenched the cases. 66.5 pretty much max unless you feel like working alum to alum which doesn't work.

Clean it up with brake cleaner and seal the pipe then find out if still leaking. Likely the pipe not sealing but you can't be sure until it is cleaned and isolated.


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PostPosted: Tue Sep 25, 2018 7:54 pm 
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Ohh, Id love to ride one of those really long stroke motors. I read that you can get +10 cranks now etc. I reckon the port timing would be all over the place and you could make so much more of ports etc, I also guess you'd need a spacer for the head as well. I'd not given it much thought until now, just never thought it would be worth the hassle.

From what youve said I'm still not convinced what youve got is a 421 as you'd need 68mm cyls and a +4 throw crank to get to that cc, or a as Evan says a longer throw crank and something that fits in the OEM bore and doesnt interfere with the PVs, but hey its your motor and youre not really telling us what you (your mechanic) did to it so I remain skeptical. Bear in mind that 66mm (really the sensible max for a PV) x +4mm throw crank is 396cc, you can work that stuff out here:

http://performancetrends.com/Calculator ... cement.php

I'd use a cheap can of degreaser, but simply looking at it with its clothes off might tell you where its coming from.

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PostPosted: Wed Sep 26, 2018 1:40 am 
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That calculator is handy. I've never seen it before. I'll bookmark that. Thanks Jon.

This formula I use is pretty simple and worth writing down for future use.

Bore (in cm) x bore (in cm) x stroke (in cm) x 0.7854 x number of cylinders.

Eg...a standard bore RZ350 would be 6.4 x 6.4 x 5.4 x 0.7854 x 2 = 347.43 CC

Using that same formula we can deduce the following:

To get a 421 you use a 68 mm bore and a +4 stroke. So...6.8 x 6.8 x 5.8 x 0.7854 x 2 = 421.27 CC

You can use a +7 stroke and 66 mm bore to get 6.6 x 6.6 x 6.1 x 0.7854 x 2 = 417.38 CC

Or, as Jon points out for the 396 motor 6.6 x 6.6 x 5.8 x 0.7854 x 2 = 396.85 CC

Hellgate hasn't told us the stroke, but based on his use of standard RZ350 cylinders and him being told there is plenty of sleeve material remaining I suspect he has a 66 mm bore and a +7 stroke to get the 417 motor. Or as Jon notes, it has to be a + 4 and 396.

If it is a 421 he has and 68 mm bores on standard RZ350 cylinders, the liners must be paper thin now and the valves significantly reworked to clearance the pistons.

As for the oil leaking issue, I'd also verify that the 3 oil seals were actually installed correctly. Often they'll be installed backwards and will leak profusely.

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PostPosted: Wed Sep 26, 2018 2:41 am 
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Thats very true John, if someone not familiar with them fits them backwards all bets on sealing will be firmly set to off...

I reckon, fro whats been said that this motor is a 65mm x +4 = 385. Just my view... maybe the OP will tell us whats in it? I'll be tickled pink if it really is a 421 with the OEM cyls as I'll plan to build one too. :smt023

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PostPosted: Wed Sep 26, 2018 1:49 pm 
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The last one i looked at had the seals in backwards. They basically just fall out. Can't imagine they hold any pressure when in backward.

Maybe the 421 is a joke we aren't getting?


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PostPosted: Sat Oct 06, 2018 9:06 pm 
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Leak solved.Image

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PostPosted: Sat Oct 06, 2018 9:13 pm 
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evan_calgary wrote:
421 on stock barrels? not unless you went +8 crank and trenched the cases. 66.5 pretty much max unless you feel like working alum to alum which doesn't work.

Clean it up with brake cleaner and seal the pipe then find out if still leaking. Likely the pipe not sealing but you can't be sure until it is cleaned and isolated.
That's pretty much the motor. Runs better and better everyday. Still breaking it in. Only 112km so far. At 300km it will go on the dyno for a step test.

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