Trying to do a leak down test on my cylinders.

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NP317
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Re: Trying to do a leak down test on my cylinders.

Post by NP317 » Mon May 03, 2021 1:15 pm

You should be able to easily determine a valve timing problem by reassembling the engine, leave the valve covers off, and manually rotate the engine to observe valve action vs piston position.
A can't imaging valve timing where NO steam/air ever gets to the cylinders! Especially when it operated before.

Separate from that, your are correct that the valve surfaces should be resurfaced, based on their visible condition in the photo.
That present condition would prevent them from sealing, allowing steam/air to leak to the exhaust ports.

Mysterious, because your described symptom implies NO steam or air are getting to either valve chest.
That issue needs to be resolved first, checking from the throttle onward. Split-point trouble shooting.
RussN

Harold_V
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Re: Trying to do a leak down test on my cylinders.

Post by Harold_V » Mon May 03, 2021 6:41 pm

Emfinger wrote:
Mon May 03, 2021 10:45 am
Anyone know where I can buy new rings 2.350" x .090" ?
Seems a rather strange bore diameter. Before you place an order for rings, double check your measurement. I'd be inclined to think that the bore is 2.375" (2-3/8"), not 2.350", which is bastard.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

Emfinger
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Re: Trying to do a leak down test on my cylinders.

Post by Emfinger » Mon May 03, 2021 6:43 pm

Harold_V wrote:
Mon May 03, 2021 6:41 pm
Emfinger wrote:
Mon May 03, 2021 10:45 am
Anyone know where I can buy new rings 2.350" x .090" ?
Seems a rather strange bore diameter. Before you place an order for rings, double check your measurement. I'd be inclined to think that the bore is 2.375" (2-3/8"), not 2.350", which is bastard.

H
Thanks....I know how to read a micrometer !

Emfinger
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Location: Yucca Valley, CA

Re: Trying to do a leak down test on my cylinders.

Post by Emfinger » Mon May 03, 2021 6:45 pm

It turns out there no surface grinders in Yucca Valley, CA

Harold_V
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Re: Trying to do a leak down test on my cylinders.

Post by Harold_V » Mon May 03, 2021 6:47 pm

Emfinger wrote:
Mon May 03, 2021 6:43 pm
Harold_V wrote:
Mon May 03, 2021 6:41 pm
Emfinger wrote:
Mon May 03, 2021 10:45 am
Anyone know where I can buy new rings 2.350" x .090" ?
Seems a rather strange bore diameter. Before you place an order for rings, double check your measurement. I'd be inclined to think that the bore is 2.375" (2-3/8"), not 2.350", which is bastard.

H
Thanks....I know how to read a micrometer !
So do I, and I've been reading them since 1956. Doesn't mean I haven't made a mistake in my reading. <shrug>

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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Bill Shields
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Re: Trying to do a leak down test on my cylinders.

Post by Bill Shields » Mon May 03, 2021 8:18 pm

Could be 60 mm..

But given the profiles of the slide valves it could well be that the bore started at an intended 2.3125 and ended up there they are by the time they were finished.

Questions

...what is the OD of each piston?

Is the bore of the cylinders consistent from one end to the other? Before you think about rings you need to know what you have to work with.

Note: you do not necessarily need surface grinder to get where you want to go.
Too many things going on to bother listing them.

Harold_V
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Re: Trying to do a leak down test on my cylinders.

Post by Harold_V » Tue May 04, 2021 1:53 am

Bill Shields wrote:
Mon May 03, 2021 8:18 pm
Could be 60 mm..
A bit undersized for that, so not likely.

That the bore may measure as posted isn't a surprise, assuming the builder made his own rings, or had a source for bastard sizes. If that isn't the case, I'm more than perplexed on why anyone would choose a size that isn't standard. It really complicates things when you need parts.
Note: you do not necessarily need surface grinder to get where you want to go.
I agree. There's more than one way to accomplish an acceptable surface (flat and smooth), although a surface grinder often makes it a lot easier. Personally, assuming I didn't have access to a surface grinder, I can't see any reason why I wouldn't fly cut the surfaces. An exceptional finish can be achieved in the hands of someone who understands machining.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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David Powell
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Re: Trying to do a leak down test on my cylinders.

Post by David Powell » Tue May 04, 2021 3:52 am

I have met some really weird and initially baffling faults with slide valves and their associated pieces, Be quite sure that the valve rod actually moves the valve as intended. I have met valve rods with partially stripped threads that would drive the valves when turned by hand but jump free or change position when trying to drive the valve when there was air or steam pressure on the valve. Similiarly some that were secured with set screws where the screws had worn the dimples they originally fitted in to endways into slots, Be suspicious of everything. Regards David Powell.

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Bill Shields
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Re: Trying to do a leak down test on my cylinders.

Post by Bill Shields » Tue May 04, 2021 3:59 am

For just such real world experiences I have made a set of lexan valve covers so that I can watch the valve action while operating under pressure.

As David says....never be surprised by what you do or do not see
Too many things going on to bother listing them.

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