Author Topic: 15cc Seal and 30cc Seal Major  (Read 11290 times)

Offline b.lindsey

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Re: 15cc Seal and 30cc Seal Major
« Reply #90 on: July 02, 2019, 09:56:54 PM »
Halfway there on the Pistons for both engines. Nice work. Hope the ring making goes just as smoothly for you.

Bill

Offline Jo

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Re: 15cc Seal and 30cc Seal Major
« Reply #91 on: July 02, 2019, 10:06:13 PM »
Thanks Bill  :)

Hope the ring making goes just as smoothly for you.

Its not the making that I am worried about. The Seal ones are 16mm diameter and 1mm square so there is a high probability of breaking them when trying to fit them to the pistons if the heat treatment is not spot on  :paranoia: The Major's ones are not much better 

Jo
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Offline Roger B

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Re: 15cc Seal and 30cc Seal Major
« Reply #92 on: July 06, 2019, 10:45:00 AM »
1mm square is big for a 16mm bore. I think I ended up with 0.8mm deep having broken most of the 1mm ones. 0.5mm was too thin.
Best regards

Roger

Offline Jo

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Re: 15cc Seal and 30cc Seal Major
« Reply #93 on: July 06, 2019, 07:55:27 PM »
Thanks Roger  :) I made a point of discussing ring thickness today at the Guildford show and the boys agreed with you 0.7 to 0.8mm thick is probably good  :ThumbsUp:

I was in trouble with Vixen as I failed to take these two engines to the show today   :facepalm2:

Jo
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Offline Jo

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Re: 15cc Seal and 30cc Seal Major
« Reply #94 on: July 07, 2019, 02:17:02 PM »
Piston Rings are done  :)

These are a simple turning exercise: Turn the outside to fit the bore, bore the inside to leave the required ring thickness (1mm for the Major and 0.75mm for the Seal) score the inside with the boring tip then using an old slitting saw blade as a parting off tool slice off the rings.

Finally give the rings a rub on wet and dry paper on each side to clean up the surface. This is not as easy as it sounds  :ShakeHead: It is very easy to end up with a ring that is thinner on one side than the other so it is worth checking with a micrometer. I used a pot chuck to hold the ring while giving it a rub on the paper.

Split the ring by holding the ring in a vice with the score line right on the edge and using a pair of parallel action pliers gently rock the ring until it breaks. I clean up the ends after heat treating.

My version of heat treating is to spring the rings round a bit of steel then hang them in the hearth. The rings are then gently heated and as they take the set they loose their springiness so drop off the bit of steel. These are then allowed to cool at their own pace still surrounded by the heat in the hearth. Once cool the rings can have their ends filed to give the appropriate gap when fitted to the bore.

I checked one ring to make sure it did not want to break when sprung over the Major piston and it survived so now that I have my set of rings it must be time to finish off those pistons.

Jo
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Offline b.lindsey

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Re: 15cc Seal and 30cc Seal Major
« Reply #95 on: July 07, 2019, 02:24:18 PM »
Nice work on those rings Jo. Did you make any spares....just in case?

Bill

Offline Jo

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Re: 15cc Seal and 30cc Seal Major
« Reply #96 on: July 07, 2019, 02:25:31 PM »
Thanks Bill, there is one spare ring for each engine so I will have to be careful  :paranoia:

Jo
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Re: 15cc Seal and 30cc Seal Major
« Reply #97 on: July 07, 2019, 08:03:22 PM »
Jo, They look great! The rings Kirk supplies are .8mm thick. How much smaller did you make the pistons for the Seal? I will make mine this week, liners were lapped and fitted yesterday, hope to make the valve cages later today
cheers
Mark

Offline Jo

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Re: 15cc Seal and 30cc Seal Major
« Reply #98 on: July 08, 2019, 07:45:43 AM »
Is the 0.8mm for the Major or Seal Mark? I did my Seal ones about that size.

How much smaller did you make the pistons for the Seal?

I made mine a rattling good fit  ::) What that means is reasonable fit in the liner but if you put your fingers over top and bottom and shake it too and fro it is free moving in the liner  :) If I had done cast Iron pistons they would have been lapped to fit and would wear in on the first run.

Jo
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Re: 15cc Seal and 30cc Seal Major
« Reply #99 on: July 08, 2019, 09:29:14 AM »
Jo, .8 for the Seal. Well actually 1/32" in the old language . So do you think .1mm smaller for the Pistons? Or a bit more??

Thanks
Mark

Offline Jo

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Re: 15cc Seal and 30cc Seal Major
« Reply #100 on: July 08, 2019, 12:26:44 PM »
Nearer to -0.02mm. Test the liner on the piston as you turn it down.

Jo
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Re: 15cc Seal and 30cc Seal Major
« Reply #101 on: July 08, 2019, 07:59:57 PM »
Jo,
thanks, thats not as much as I was thinking!

cheers
mark

Offline Jo

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Re: 15cc Seal and 30cc Seal Major
« Reply #102 on: July 09, 2019, 11:59:53 AM »
All the rings are on the pistons. They are a bit fragile and there was one breakage  :Doh: The biggest challenge was getting the bottom ring on. I chose to put them on in reverse and slide them up the piston by pushing the piston into the bore of the cylinder.

The drawings show the bottom of the liner is chamfered, this is to enable the pistons with their rings to be easily inserted into the liners. Of course this has not been done on either of the engines  :ShakeHead:. It is possible to put the pistons in from above but it is a bit of a challenge so I have decided to add the chamfer, which would have been so easy on the lathe before fitting the liners  :facepalm:

This is going to be done from the bottom which needs a longer boring bar than I have so I have had to make another chamfering bit out of silver steel. I will cheat and do this machining holding the cylinders in a vice. This will require my big heavy vice on the table so time to get the roller skate out.

I probably won't get this finished today as I have other jobs to do  :toilet_claw:

Jo
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Offline Laurentic

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Re: 15cc Seal and 30cc Seal Major
« Reply #103 on: July 09, 2019, 12:19:10 PM »
To put the pistons into liners from the top generally needs either a clamp making up which clamps around the piston compressing the rings into their grooves but not too tightly done up so as to stop the piston being gently pushed through it and into the liner, or, a fixture fitting around the top of the liner with a bore tapering from uncompressed ring diameter down to liner bore diameter, with a short parallel section at liner bore diameter at the bottom, to push the piston and rings through.  Both methods benefit from the use of oil, copious amounts in the case of the second method, which is how we did it on big ships.

I appreciate this is teaching granny to suck eggs stuff to most folk on here but I mention it to others who might not know.   :old:

Chris

Offline Jo

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Re: 15cc Seal and 30cc Seal Major
« Reply #104 on: July 09, 2019, 12:22:45 PM »
Thanks Chris, it is always worth mentioning other methods  :ThumbsUp:

 :thinking: I could make a tapered brass piston fitting jig... rather than doing all the chamfering - it would be much quicker..

Jo
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