Tapered head / cylinder interface

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Tapered head / cylinder interface

This topic has 12 replies, 10 voices, and was last updated 20 March 2012 at 01:03 by David Paterson 4.

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19 March 2012 at 02:15 #22051
David Paterson 4
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@davidpaterson4
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19 March 2012 at 02:15 #87526
David Paterson 4
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@davidpaterson4
I was showing off my first scratch-built engine yesterday and was asked about head gaskets by the viewer.

He referred to old Ducatti – about which I know nothing – and said that they had eliminated the need for head gaskkets by making the cylinder/ /head interface a tapered fit. He asked if anyone did this as model engineering practice.

Any thoughts?

My model is the Opus Prime from the ME collection vol1. 3/8 bore so pretty challenging to get any head bolt tension with 12BA I would have thought

Dave P
19 March 2012 at 07:49 #87534
Ian S C
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@iansc
When people ask me if / or say I should do something difficult, my reply usually is,"have you done it that way", I would like to see it. More often than not the person has never actually ever built anything, but they seem to know all about it. Ian S C
19 March 2012 at 09:02 #87536
Ady1
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@ady1
they had eliminated the need for head gaskkets by making the cylinder/ /head interface a tapered fit.

From my own amateur car tinkering and lathework I would guess that they still use something like gasket sealant in the join.

If you had any sealing problems from even the tenniest of errors in a taper the engine would be a writeoff.

I presume that at assembly time a special machine secured the head to the block, otherwise you might get a slight "sliding twist" on a steep taper or a shallow taper would jam the head into the block (like an MT2 taper), creating distortion issues.

I don't actually know of a single manufacturer who does it.

Edited By Ady1 on 19/03/2012 09:03:04
19 March 2012 at 09:17 #87538
PeterB
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@peterb58166
Dave,

Maybe the viewer who commented was getting mixed-up with a slightly different motorcycle practce used by some of the more innovative manufacturers, such as Vincent-HRD. They use a CI liner with a larger dia top standing slightly proud of the top of the cylinder. The head is then ground on to the liner top with an oscillating rotary motion using fine paste. No tapers anywhere. The seal is permanent until next disturbed and works extremely well, allowing much better heat transfer.

But hey, take heart from Ian's post above – I suspect he is on the nail here. Celebrate your own success!

Regards,

Peter B
19 March 2012 at 09:44 #87542
Baldric
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@baldric
I think you will find that the valve covers on standard GWR cylinder blocks are fitted like this, occasionally you do see a gasket but it is loose so does nothing!
19 March 2012 at 10:29 #87545
Gordon W
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@gordonw
I can't think of any with a taper seal, but no doubt there will be one. Gasket -less seals are / were fairly common. Vincents,as mentioned, speedway JAPs, and my favourite the 2CV, of which I have repaired many and never had a head leak. The standard method is to grind/ lap the spigot to head, use coarse paste on the spigot and fine paste on the head/cylinder joint. this way you should get a seal on both faces. Does this make sense?
19 March 2012 at 11:16 #87549
Jeff Dayman
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@jeffdayman43397
I've worked on plenty of Ducati and other bikes and don't recall ever seeing one with a tapered head/cyl interface. All the ones I've seen had a normal head gasket. Not saying they never made one that way, but again I've never seen one in person or in any books on the subject.

A ground or lapped tapered joint is one of the most expensive joints to make. It is very prone to leak if there is any heat distortion of either part, and very hard to repair. None of these attributes is a good thing on a bike, especially if air cooled.

The usual rolled soft metal ring sandwiching a fibre sheet makes a very good high temp head gasket that will last many years in a bike and is cheap as chips to make. For racers, a soft copper o-ring is sometimes used in a cut groove, or a soft copper strip rolled into an S shaped ring is sometimes used in a cut groove. These are not nearly as costly as a ground. lapped joint, and give very positive high pressure high temperature sealing while not being as badly affected by distortion by heating.

In any case, with high performance engines the main compression leak source when you get to a high state of tune and high HP per CC is the piston rings, not the head and valves.

JD
19 March 2012 at 11:51 #87552
Ken Johnston
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@kenjohnston10955
As Peter B and Gordon W said, Vincents have a lapped head/cylinder joint. The coarse paste used on the alloy cylinder muff taken off more material than the fine on the liner top. The seal is then between the cylinder liner and the head. And of course you only need a touch of lapping to maintain the seal.
19 March 2012 at 13:52 #87565
Gordon W
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@gordonw
Yes I got it the wrong way round, Fine paste on the spigot, coarse paste on the head / cylinder joint. Then the joint is at the spigot top.. Never got it wrong when doing the job for real. Should have stayed in bed.
19 March 2012 at 14:44 #87570
MICHAEL WILLIAMS
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@michaelwilliams41215
Dry fitted taper in taper joints are common in the aerospace industry . Numerous different ways to do it but most usual are :

Loose ring tapered both ways into tapered sockets on each part .

Male taper on one part and female taper on other part .

Tapers used are certainly much flatter then Morse taper and are usually flatter than a normal union nut olive and are always self releasing .

Taper in taper joints are also used sometimes in the Chemical industry and a few other aplications .

Rarely seen but not unknown is the double touch tapers plus flat surfaces connector . In this a male taper seats in a female taper and at the same time flat surfaces on each part seat against each other . Used for very high integrity pipe joints .

The basic idea of the above has been developed for another purpose altogether by Schaublein . They use the taper plus flat type seating for their very high accuracy tool shank system for micro machining centres .

Michael Williams .
19 March 2012 at 20:35 #87609
Sub Mandrel
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@submandrel
There was a car maker who didn't use gaskets (Bugatti?)

Gaskets are cheaper, easier and more reliable, especially for multi-cylinder engines, as they can cope with a small amount of warp.

So tell you helpful friend that it may be a demonstration of skill, but it isn't the best engineering solution.

Neil
20 March 2012 at 01:03 #87629
David Paterson 4
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@davidpaterson4
Thanks for all of your responses.

I don't think he was being critical. He is a high scholl tech teacher who has his students building stuff in Western Australia. his hobby is race cars, he builds chassis for then appparently, so he was really pretty engaged.

I had some trouble sealing this engine, particularly the bottom cylinder head, and its still not all that flash. My father is a great fan of the 2CV – he drives one regularly and I dimantled the cylinders for replacement for him not long ago. My current task is fabricating suspension components for a '38 Sunbeam in restoration – broke a slot cutter and had to make a new one, so new skills all the time and not just models.

so, thanks all, and I will think about how to use this. I keep thinking that tapered threads on boiler fittings might be a good idea, but how do you do that on a lathe? Or is it only practical with some sort of tapered die at this scale? Same concept but potentially more applicable at this scale?
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