Author Topic: Stuart 7A Build  (Read 11851 times)

Offline Gas_mantle

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Re: Stuart 7A Build
« Reply #15 on: May 18, 2018, 07:58:29 AM »
Does this valve rod hole/guide actually do much to affect performance on small engines ?  Presumably the inward steam / air pressure will seat the valve adequately?

The casting I have for a no4 engine doesn't have the cast protrusion although there may be sufficient thickness in the valve chest wall to drill into. (I haven't got that far yet so haven't properly looked into it)

Offline warrenmaker

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Re: Stuart 7A Build
« Reply #16 on: May 18, 2018, 09:37:21 AM »
I spat the dummy with the old part and started afresh. MB when I get the urge I will go back and repair it the way you suggested Jason. Thanks for the tip.

Here is new valve chest from scratch and the cover.

Offline Gas_mantle

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Re: Stuart 7A Build
« Reply #17 on: May 18, 2018, 05:50:30 PM »

Yes the castings came direct from Stuart. I also have a #4 part set of casting I picked up at a flea market. They are dated from 1977. They are FAR Superior to the #7 I have purchased for this build .

The old style 10v trunk guide I was given is far superior to the modern set of castings I recently bought, it also has a better profile. (the old one is on the right)





I'll be interested to compare the two after machining.


Offline Larry Sw

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Re: Stuart 7A Build
« Reply #18 on: May 18, 2018, 06:49:43 PM »
It looks like the old style has much better support for the Cylinder with larger braces.

Larry

Offline Jasonb

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Re: Stuart 7A Build
« Reply #19 on: May 18, 2018, 08:16:20 PM »
If that is a genuine Stuart one it must be over 35yrs old as the one I made in my teens has the same taper as the "new" one in your photo

Offline Gas_mantle

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Re: Stuart 7A Build
« Reply #20 on: May 18, 2018, 08:18:08 PM »
It's the one Jo gave me so I don't know anything about its origin

ChuckKey

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Re: Stuart 7A Build
« Reply #21 on: May 18, 2018, 10:19:06 PM »
Does this valve rod hole/guide actually do much to affect performance on small engines ?
The valve rod needs guiding at the tail end to stop it waggling about in the stuffing box, making it wear quickly and therefore hard to keep steam tight.
The more complicated alternative is an externally guided valve crosshead. In full size you often have both so that the gland is not required to support the rod at all and can float.

Offline warrenmaker

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Re: Stuart 7A Build
« Reply #22 on: May 20, 2018, 08:20:04 AM »
Bit more done today,

The alignment shaft is an extremely useful item for aligning the bearings Standard and cylinder.   :cartwheel:


Offline warrenmaker

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Re: Stuart 7A Build
« Reply #23 on: May 20, 2018, 10:16:59 AM »
I have no idea how to cut the radius shown on the drawing in the end of the crosshead.... :headscratch: :headscratch:

I'm guessing I need to grind a rounded trepanning tool....

Here is my half hearted attempt using a DCMT insert.    :facepalm:

Any suggestions would b appreciated thanks..

Offline Jasonb

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Re: Stuart 7A Build
« Reply #24 on: May 20, 2018, 10:29:17 AM »
Triangular file will have it done faster than you can make a bit and set it up for the cut. But It won't put back the bi of metal you did not need to remove.

Offline warrenmaker

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Re: Stuart 7A Build
« Reply #25 on: May 20, 2018, 10:43:14 AM »
AH ... yes,, I see what u mean.  It seems I have created a difficult situation for myself. A tri file will be little use to me now with what I have done..  :Doh:

Oh well. Its a custom cut cross head.  8)

Offline warrenmaker

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Re: Stuart 7A Build
« Reply #26 on: May 22, 2018, 06:33:23 AM »
OK.... it seems I have fooked up BAD this time.... :help:   :help:   :help:


Offline warrenmaker

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Re: Stuart 7A Build
« Reply #27 on: May 22, 2018, 06:35:14 AM »
I basically tried every which way to stuff this piece up. and finally I did, second last operation and it grabbed whilst trying to drill the pin hole.

I don't think this is fixable.... :facepalm:

My biggest problem I think is not having the correct "order of operations",, which I am finding out is critical with these types of parts that have so many operations per piece.

Would any body be so kind as to list them for me please for this part. ...I am gutted ! 

Offline Jasonb

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Re: Stuart 7A Build
« Reply #28 on: May 22, 2018, 07:06:41 AM »
I'll leave the method to one of the casting fans.

You could save the bottom half and make a top from steel. If you cut off the rod about 6-8mm above the bearing it can be drilled out and tapped to take a new forked rod. Or cut it off flush and make a steel one with a flanged end which is more prototypical of a marine conrod. Either way you won't have to contend with soft gunmetal.

« Last Edit: May 22, 2018, 07:12:47 AM by Jasonb »

Offline warrenmaker

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Re: Stuart 7A Build
« Reply #29 on: May 24, 2018, 01:11:02 PM »
OK.. so. after some judicious panel beating ... and a little end bushing. we r back on track...  ;D

 

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