how much blowby is acceptable?

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geraldtson
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Re: how much blowby is acceptable?

Post by geraldtson » Sat Aug 04, 2018 6:58 pm

Other than the color of the blowby (blue smoke) it sure sounds comparable to water getting into cylinders somewhere. I'd pull of the radiator cap and bring the temperature up and look for bubbles (compression) in the water system. I don't care for the MLS gaskets have had them leak water slowly after a few months with only minimal usage with brand new blocks and heads (especially aluminum) and fasteners and such. I go out of my way to not use them but one failing so quickly in your case is unlikely. Everything has to be right to have success with them.
Did you tell your machinist you were using a Steel-PlasMoly ring? What finish did he put on cylinders? 400-600 grit? Was a torque plate used?
Like someone else posted Why the 320? And what type of honing fluid did you use for the 320?
If there's no air bubbles (compression) in radiator or losing water out exhaust next thing i think i'd do is pressure test on water system if that show's nothing then do a cylinder leakdown test that will tell you about the blowby as well as any other issues you might have.

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Re: how much blowby is acceptable?

Post by AC sports » Sun Aug 05, 2018 12:11 am

I got round to doing a compression test yesterday.
Dry: all 176-180 psi
Wet: all 200 psi +-3psi

So does everyone agree the 320 grit flexhone I finished with is too fine?
What's appropriate for those rings ?

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Baprace
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Re: how much blowby is acceptable?

Post by Baprace » Sun Aug 05, 2018 1:29 am

AC sports wrote:
Sun Aug 05, 2018 12:11 am
I got round to doing a compression test yesterday.
Dry: all 176-180 psi
Wet: all 200 psi +-3psi

So does everyone agree the 320 grit flexhone I finished with is too fine?
What's appropriate for those rings ?
On a CK-10, I use either 820 or 818 ( 400 gr) finish with a couple of strokes of brush on most High Perf engines that I am going to start on the dyno, if the customer is going to start the engine then I use 625 or 623 (320 gr) finish and have no issues with rings seating. I use a minimum of 4 stages of stones and a couple of strokes of brush on customer starting engine and a maximum of 5 stages with an additional brush set on engines we start. I do not use a flexhone. I can't say anything bad about flexhones , just stating how we do it at my shop. We also use only Brad Penn oil.

AC sports
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Re: how much blowby is acceptable?

Post by AC sports » Sun Aug 05, 2018 1:59 am

Looking at the wet-dry compression test results would you all agree there is a sealing issue? It's about a 12% variance . New engine just clicked over 1000mls.
BTW is a 320 flexhone finish the same as a 320 stone finish? It looks way finer to me.

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Re: how much blowby is acceptable?

Post by user-23911 » Sun Aug 05, 2018 5:52 am

It's not so much the blowby gas that's the problem, it's the oil which lowers octane and makes a mess.

To me the fix is to strip it, take it back to the machine shop, get them to hone it properly AGAIN.
The clearances will be a bit more.

This time leave it alone, don't use the crap flexihone.

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Re: how much blowby is acceptable?

Post by mag2555 » Sun Aug 05, 2018 6:27 am

Your hate for Flexhones leaves me scratching my head as to why!
I have never had issues when using the proper grit for a given type ring.

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Re: how much blowby is acceptable?

Post by geraldtson » Sun Aug 05, 2018 7:36 am

320 is not to fine for that ring package. Call JE and see what they recommend.

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Re: how much blowby is acceptable?

Post by Baprace » Sun Aug 05, 2018 5:23 pm

AC sports wrote:
Sun Aug 05, 2018 1:59 am
Looking at the wet-dry compression test results would you all agree there is a sealing issue? It's about a 12% variance . New engine just clicked over 1000mls.
BTW is a 320 flexhone finish the same as a 320 stone finish? It looks way finer to me.
I wonder if your 320 flexhone has glazed the cylinder wall from not having enough stone pressure on the surface.

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Re: how much blowby is acceptable?

Post by JoePorting » Sun Aug 05, 2018 8:16 pm

I was thinking that over-heating the motor may have glazed the cylinders. But in either case, I wouldn't worry too much about it. If the motor runs and sounds good, then just keep driving it. Just keep an eye on the water and oil level.
Joe Facciano

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Re: how much blowby is acceptable?

Post by MadBill » Sun Aug 05, 2018 8:59 pm

You mention not exceeding 50% throttle during break-in. Recommendations vary, but many (including me) feel that short bursts of WOT are important for ring seating. At this point I'd try flogging it as hard as possible to see if the higher resulting ring forces can do the job.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.

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Re: how much blowby is acceptable?

Post by user-30257 » Sun Aug 05, 2018 9:23 pm

MadBill wrote:
Sun Aug 05, 2018 8:59 pm
You mention not exceeding 50% throttle during break-in. Recommendations vary, but many (including me) feel that short bursts of WOT are important for ring seating. At this point I'd try flogging it as hard as possible to see if the higher resulting ring forces can do the job.
Yeah, pretty much we get the engine to temp, check for leaks, timing, lash. And beat the piss out of it until it makes what it makes.

I don't see any reason in pussyfooting an engine. If it's meant to spend its life a 2000rpm, cool.. but thsts rarely the case.

Unless you bought some rings from 1960 that need to be lapped into a round shape, run it like you stole it.

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Re: how much blowby is acceptable?

Post by AC sports » Sun Aug 05, 2018 11:26 pm

Do the wet - dry compression test results confirm its a ring issue? What sort of variance should there be between wet and dry?
Dry: 176-180 psi
Wet: 200 psi

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Re: how much blowby is acceptable?

Post by bentvalves » Sun Aug 05, 2018 11:32 pm

how did you clean the bores before final assembly ?

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Re: how much blowby is acceptable?

Post by Leftcoaster » Sun Aug 05, 2018 11:54 pm

You don't say whether the pistons are flat top, dished, or a combination - -

How do you know the fluid, presumably oil, introduced for the wet compression test was bathing the top rings?

- - unless you added a substantial quantity, which of course increases the compression ratio and therefore cranking pressure regardless of ring seal

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Re: how much blowby is acceptable?

Post by AC sports » Mon Aug 06, 2018 12:16 am

Bores were scrupulously clean prior to assembly.
Pistons have a 13cc truncated conical dome.
Minimal engine oil was squirted into the bores and then engine cranked to disperse it. It would not have been more than 1 cc. The pressures also came up quicker on the wet test.
I stuck a micro camera down the bores. The cross hatch is visible and they don't seem glazed as far as i can tell.

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