What is that bore measuring device? I've never seen one like that. Please, teach me something.
Grasshopper
Grasshopper
Re: crooked core in cyl casting
- Thread starter woffler
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Nice one Woffler. I would have suggested a liner - that bush sounds like a simple accurate and practical liner for the bore.
What pressure are you expecting to run at? Maybe you could have simply made oversized pistons? - depends on the minimum wall thickness after you managed to clean-up at 1.25". I would be very careful with the interference dimensions when you fit the liners. The interference develops hoop stresses in the iron body - which is liable to crack or split completely if very thin. If the liner is a "just-about-tight", or sliding fit, (rather than needing a press to fit) then it will be secured from moving by the end caps. Loctite products can help secure a liner - but the wrong one will cure too quickly and may lock the liner in place when "half-in and half-out". So be very careful with the sizes and check interference fit tables for a fit closest to sliding, rather than risk breaking the cylinders. Remember, the bronze will expand more than the cast iron when you get to "steam temperature" - so that also adds to the hoop stress trying to split the cast iron asunder. Having done the calculations to prove a designer picked the wrong "fits" for a component fitted to a car engine block, (Differential expansion and contraction causing cracking of the outer component) I have first hand experience of how this can easily go wrong.
I think for your "fit" I would check calculations, fit tables, etc. Then check the bore ID and liner OD, Hone the bore to suit the fit dimensions for the tables, say for the tightest sliding fit on the liner OD, and then fit the liner with a drop of Loctite added when the liner has been slid 3/4 of the way into the iron cylinder (Only if you want to add any Loctite). As a lad (1960s) I fitted dozens of liners into diesel engine blocks - after boring and honing the block for the correct fitting dimension for the liner. Then using the hydraulic press (Never a hammer/shock loading!) could "feel" the liner going in with a stick-slip motion - sometimes almost a "groan" but they were cast iron liners in a cast iron block, but were secured from moving by the cylinder head, so an "easy" fit was ideal. Anyway, we had to re-bore the liners to size after fitting to get the size, as the liners were always supplied thicker-walled than after finished boring. But I doubt you should need that extra process.
Keep up the good work!
K2
What pressure are you expecting to run at? Maybe you could have simply made oversized pistons? - depends on the minimum wall thickness after you managed to clean-up at 1.25". I would be very careful with the interference dimensions when you fit the liners. The interference develops hoop stresses in the iron body - which is liable to crack or split completely if very thin. If the liner is a "just-about-tight", or sliding fit, (rather than needing a press to fit) then it will be secured from moving by the end caps. Loctite products can help secure a liner - but the wrong one will cure too quickly and may lock the liner in place when "half-in and half-out". So be very careful with the sizes and check interference fit tables for a fit closest to sliding, rather than risk breaking the cylinders. Remember, the bronze will expand more than the cast iron when you get to "steam temperature" - so that also adds to the hoop stress trying to split the cast iron asunder. Having done the calculations to prove a designer picked the wrong "fits" for a component fitted to a car engine block, (Differential expansion and contraction causing cracking of the outer component) I have first hand experience of how this can easily go wrong.
I think for your "fit" I would check calculations, fit tables, etc. Then check the bore ID and liner OD, Hone the bore to suit the fit dimensions for the tables, say for the tightest sliding fit on the liner OD, and then fit the liner with a drop of Loctite added when the liner has been slid 3/4 of the way into the iron cylinder (Only if you want to add any Loctite). As a lad (1960s) I fitted dozens of liners into diesel engine blocks - after boring and honing the block for the correct fitting dimension for the liner. Then using the hydraulic press (Never a hammer/shock loading!) could "feel" the liner going in with a stick-slip motion - sometimes almost a "groan" but they were cast iron liners in a cast iron block, but were secured from moving by the cylinder head, so an "easy" fit was ideal. Anyway, we had to re-bore the liners to size after fitting to get the size, as the liners were always supplied thicker-walled than after finished boring. But I doubt you should need that extra process.
Keep up the good work!
K2
Hi,
Just a thought, if the liner is left 'loose' in the outer casting (i.e. without loctite or some locating method) is there not a possibility of the steam ports getting out of alignment if the liner were to rotate? As you quite rightly say if the fit is a tightish frictional one differential expansion of the components could cause problems.
Just did a quick check as my memory is not what it was and saw that the coeffiecient of thermal expansion are greater for bronze than cast iron - around 1 1/2+ times, so as you say a look at the fits tables might be prudent to prevent cracking the thin shell..
Stay safe and healthy,
TerryD
Last edited:
Hi David,
Sorry for delayed response. The device is home-made.
Not my design, the original appeared in Model Engineer magazine some time in the seventies. I did not own the magazine but thought the design interesting so scribbled some notes and sketches in my notebook and used them as a basis for the version I built some time later (changes to design occurred to fit in with locally available materials, contents of scrap bin, etc at the time)
I can post you some better pics and some drawings if you like.
All the best,
Ian
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I certainly would like to see some more detail on your device. I see the general concept but it would be nice to not have to reinvent the wheel.
I would like that as well.
Rotormac
Member
The original design was by L C Mason and appeared in the Model Engineer magazine for January 4th 1980.
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Thank you. It turns out that I have a CD that I purchased some time back with back issues of Model Engineer and it has that issue included so I printed it. Not sure what copyright issues are on these.
CD is breach of copyright and posting here would be too.
Rotormac
Member
Written copyright extends for 70 yrs after the death of the author.
I've modified LC's design slightly to accommodate the dial gauge I had and I'll happily post drawings of the principal parts of my unit.
The only tricky bit is the main plate. Getting the geometry correct is tedious but fun.
I've modified LC's design slightly to accommodate the dial gauge I had and I'll happily post drawings of the principal parts of my unit.
The only tricky bit is the main plate. Getting the geometry correct is tedious but fun.
Do you have any drawings of this, please?
There is no excuse for an offset core like that.
.
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Alec Ryals
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Hello , I Sleeved mine with cast iron
Alec
Alec
THe reason I write in bold, it's so my almost 80 year old eyes can actually see what I'm writing.Grasshopper, would you mind awfully, turning the bold off?
That quote is two years old. No problem. I understood your explanation at the time.
This is an obvious casting defect with both castings suffering from the same flaw. The core is out of position in the mold. I think they owe you a good casting. The only way to correct this is oversize the bore as another member suggested, if there is room to fit all the other bolt patterns. But boring it out will take a lot of work. I think if PM wants to keep their reputation they will rework their castings and it makes sense to be talking to them
