Author Topic: ETW's Wyvern Gas Engine  (Read 25704 times)

Online Dave Otto

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Re: ETW's Wyvern Gas Engine
« Reply #135 on: July 24, 2013, 12:42:39 AM »
Hi Rod

I have been following along with your build of the Wyvern and enjoying your progress.

I feel your pain on the head; I did a similar mistake on the exhaust valve chest for my Pacific engine. When I milled the D shaped exhaust port I did it upside down and cut into the valve seat instead of underneath it  :wallbang:. As you have decided I could have also fixed it but found it easier to just order a new casting and get on with it.

Thanks for taking the time to document and post your build here on MEM.

Dave

Online Jo

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Re: ETW's Wyvern Gas Engine
« Reply #136 on: July 24, 2013, 09:30:29 AM »
Rod, Have you thought of boring it out and making up a cast iron "plug" and having another go?

Jo
Usus est optimum magister

Offline steamer

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Re: ETW's Wyvern Gas Engine
« Reply #137 on: July 24, 2013, 09:33:39 AM »
Rod, Have you thought of boring it out and making up a cast iron "plug" and having another go?

Jo

Yes....Give it a shot...you have nothing to loose but trying at this point.

Dave
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Damned ijjit!

Offline NickG

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Re: ETW's Wyvern Gas Engine
« Reply #138 on: July 24, 2013, 11:15:04 AM »
Rod, sorry to hear about this. Hope you come up with solution.  :ThumbsUp:

Offline tangler

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Re: ETW's Wyvern Gas Engine
« Reply #139 on: July 24, 2013, 01:00:23 PM »
Hi guys, thanks for sharing my pain  :)  OK, I've had a restless night to think about this.  A cast iron plug is out, bearing in mind this is an aluminium head, because the thermal expansion co-efficient of ally is about twice that of iron so the plug would probably become loose at operating temperature.  Here's an extract from the drawing (Moderators - is this OK?).  The exhaust valve is the same as the inlet valve in my version (apart from the flange)



An ally plug might work.  It would need to be a light press fit to keep things gas tight.  The valve assembly would keep the plug from moving upwards and if I put a small top hat flange on the plug that would stop it dropping down - like this



 I think it would work but I'm still inclined to think it's a bodge too far.  I'll give it a go, if only as an exercise.


Online Jo

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Re: ETW's Wyvern Gas Engine
« Reply #140 on: July 24, 2013, 03:13:47 PM »
I was planning on putting cast iron plugs in my Galloway head as I am not happy on the aluminium valve seats. I have seen one of Malcolm Stride's drawings with an iron valve guide in an ali head  ;).  But my Centaur has studded on brass ones  :headscratch:

The head is fairly small, so relative expansion will be only a little .. a good press fit to start...

No problem with the extract. Uk copyright law allows you to publish extracts for the purpose of supporting discussion.

Jo
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Offline NickG

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Re: ETW's Wyvern Gas Engine
« Reply #141 on: July 24, 2013, 06:31:42 PM »
Yeah I initially thought yes you are right - but then as Jo said, lots of aluminium heads will have steel or iron valve seats and guides pressed into them - probably quite an interference fit mind you and not sure whether you have enough meat left for such a fit? Certainly worth a try.

Online Roger B

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Re: ETW's Wyvern Gas Engine
« Reply #142 on: July 24, 2013, 06:53:34 PM »
Almost all full size engines with alloy cylinder heads have cast iron or steel inserts. I think some used to roll a lip over the insert to keep it in place.
Best regards

Roger

Offline michaelr

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Re: ETW's Wyvern Gas Engine
« Reply #143 on: July 24, 2013, 07:12:31 PM »
When I built my Wyvern I had a problem with the valves hitting the spark plug electrode, got wrong with the boss size.

Rather than putting packing washers under the plug, I bored out the spark plug boss and pressed in a shouldered steel boss, I lightly knurled the boss and pressed it in with a coating of JB Weld on the knurling, it has never moved under running conditions or plug removing/ tightening.





Offline tangler

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Re: ETW's Wyvern Gas Engine
« Reply #144 on: July 24, 2013, 08:26:21 PM »
Many thanks for the comments guys.

I think the use of cast iron/steel is a bit of a red herring since I've used bronze inserts to overcome the valve seat in ally issue.  What I need to ensure is that any insert doesn't provide a leak path during compression.  I'm a bit reluctant to use too much pressure on a force fit since I'm not sure how much strain the the head casting can take. It is after all a slightly porous sand casting, not a hi tech alloy.  I'm very interested by michaelr's use of JB weld as a caulk since his use suggests that it can stand up to whatever temperature the head will get to.   

Thanks again

Rod

Offline Maryak

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Re: ETW's Wyvern Gas Engine
« Reply #145 on: July 24, 2013, 11:21:02 PM »
I agree,

JB Weld is your friend when inserting cast iron valve seats into aluminium heads. It's considerably cheaper than loctite and has a higher end point working temperature.

Best Regards
Bob
Если вы у Тетушки были яйца, она была бы Дядюшкой

Offline tangler

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Re: ETW's Wyvern Gas Engine
« Reply #146 on: July 28, 2013, 03:07:24 PM »
Experiments complete, I've decide to Ali weld the exhaust valve socket and JB weld the inlet.  I've bored both the sockets with a slight recess.





The exhaust plug has a screw thread to ease handling. 





First I "tinned" the plug by melting some blobs of the braze and then spreading it all around with the stainless steel brush.  The head was then heated and some braze blobbed onto the socket and stirred around with the stainless steel rod.  By this time the plug had cooled somewhat but I placed it in position on top and directed the flame at it until it slid into the socket and then twisted it around.





Looking pretty good from this angle  :)





After cooling, the inlet valve plug and socket were liberally smeared with JB weld and the plug pushed home





Ready for milling and drilling when the JB weld has cured.  The excess braze from the exhaust plug is clearly visible butting up to the JB weld on the inlet


Offline tangler

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Re: ETW's Wyvern Gas Engine
« Reply #147 on: August 01, 2013, 08:04:03 PM »
With the JB weld set I've re-bored the seats for the valves and everything now fits snugly.  The ally braze seems to have worked very well, certainly an option for fabrication.

I drilled the stud holes for fitting the valve assemblies by clamping the cylinder head seat face to an angle plate and lining up the inlet/exhaust port face with a set square, which is at 90 degrees to the valve faces.



Then drilled through, using the valve assemblies as jigs,  and tapped on the pillar tool





8BA studs for the exhaust valve



Both valve assemblies in position



Here's a couple of pictures of the combustion space.  I cleaned up the inside in the same way as I did the first time, together with a bit of tidying up with a burr in a Dremel to smooth the transitions a bit





I still need to drill through for the spark plug but as I've not decided which plug to use yet I'm leaving that for now.

I guess it will do but there's a nice new cylinder head casting on the bench whispering "do it properly" to me. I shall turn a deaf ear for the present as the inserts have become something of an experiment and I'll carry on with the botch.

Online Dave Otto

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Re: ETW's Wyvern Gas Engine
« Reply #148 on: August 02, 2013, 12:41:19 AM »
Nice save Rod!

The repair looks great :ThumbsUp:

Dave

Offline steamer

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Re: ETW's Wyvern Gas Engine
« Reply #149 on: August 02, 2013, 12:18:52 PM »
What repair I don't see no stinkin repair!...... 8)


Great job of that Rod....Like the pillar tool too!
 :ThumbsUp:
Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!