block skimming

[Captain Mike]

Hi All

I am about to remove my Ruby engine to get the block skimmed due to blowing head gasket issues, I live in Nottingham near Newark on Trent, has anybody had any dealings with engineering firms around this area they could recommended, I know most engineering shops will undertake this work but I would like some recommendations if possible, I also have a question, If I get the block and head skimmed is there a need to increase gasket thicknesses  when rebuilding ? and if anybody has a defined easy way of removing the engine any info would be appreciated

Thanks

Mike

[Reckless Rat]

If you have the top surface of the block skimmed, it is likely that the pistons, particularly #2 and #3 could hit the head under high revs. This is due to crankshaft whip. It is important, therefore that you measure the clearance between the piston crowns and the top of the block, and ensure there is at least a .020 margin of error. I would check this beforehand because you never know, the block might already have already been skimmed.

There are two solutions. Either fit a spacer shim between the block and crankcase (this requires differing sealing choices), or have the piston crowns machined.

I would advise that you let someone who knows Austin Seven engines intimately to look at your engine and give you appropriate advice BEFORE you start handing your block over to a machine shop.

I will send you a "how to remove the engine" checklist by PM

[Chris KC]

If the block is coming off anyway you may as well remove it in situ - even if you need the engine out to re-assemble it will be a lot less weight to handle in one go.

The next challenge you will face is to remove all the studs (top face, at least), sometimes it's a breeze but more likely they will resist with a vengeance.

Before you do any of this I suggest you remove the head and observe the level of the piston crowns at exactly TDC. On a 2 bearing engine it is often advised that these should be a little below the face of the block (say 20 thou) to protect against contact with the head at high rpm (due to crank whipping). I certainly wouldn't let them go proud of the block face - which means however much you remove from the block you may also need to skim from the piston crowns (forever after).

There's no need to do anything with the head gasket.

Can't advise on local contractors in Notts area I'm afraid but if no luck I can suggest people in my own neighbourhood (bit far for you otherwise).

[Charles P]

Cottrell Engineering in Clay Cross will advise you well and know A7s.
Whether the machining causes any problems depends upon how much it needs to clean up. Then you can choose between taking a few thou off the crowns or shimming the base. Both have their pluses and minuses.

Charles

[Tony Betts]

the head is not the first thing you should worry about.

head gaskets, even austins originals. were made 40 thou over standard around the bores. so you would probably hit that first, if you have anything over 30 thou piston.

the next thing, is the thickness of the gasket under the block. i think they are available in 17 thou thickness. but you also used to be able to get 27 thou. so you could loose 10 thou there. i dont know what the new cylicon gaskets compact down to.

id insist on the work being done on a surface grinder, as a grinder will take of 1 tenth of a thou at a time. were as even the best miller will take of 2 to 4 thou.

and remember the base will need a skim, so there is an accurate flat surface to stand on.

if it me, i also have the water and exhaust surfaces done at the same time. the exhaust is usually miles out.

and as KC suggests, check how high the pistons come up before you strip the engine. then you know what you are starting with.

ive used cotterells for work for the last 30 years, and would definatly recommend.

tony

[Jeff Taylor]

Cotterell Engineering have a Facebook page showing Austin 7 cranks:

https://www.facebook.com/Cotterellengineeringltd

Their facebook post on 20th February 2020 shows the quality of their block work.

[Captain Mike]

Thanks all for the advice, sounding scary now, ! I will contact Cotterell engineering and ask for advice, and thanks for the advice on pistons and gaskets
Much appreciated

Mike

[Stuart Giles]

If you have the top surface of the block skimmed, it is likely that the pistons, particularly #2 and #3 could hit the head under high revs. This is due to crankshaft whip.

That is certainly true if the car has a '37 head. Would need to be about an 1/8" crank whip if it has the cylinder head used on 35-36 cars unless the motor has a big overbore where the piston might clout the edge of the recess the early heads have.

I often skim the block face just to get the valves sitting on rather than in the block -year of grinding in/re-cutting valve seats take their toll. There isn't so much valve lift on an A7 that you can have the valve masked for first part of opening/last part of closing without losing gas flow and therefore power. If clearance to the head is a concern after skimming, you can use a shim under the block as suggested, or any company that does engine work won't struggle to skim the piston crowns, usually carried out on a mill with a simple jig, something like this:

[jansens]

On my Riley 9 engine I had to machine a step in the piston crowns as I am using longer rods and the piston tops would otherwise hit the gasket/head. I did it in my little lathe with a fixture suggested to me by one of the experts in the club here.

The Riley pistons have a machined step in the bottom of the piston skirt so you machine up a circular steel disc with a step in it to match the piston crown. So the piston sits centralised on the disc. In the centre of the disc is a hole for a bolt to pass through. You make up a 'fake' gudgeon pin and drill and thread a cross hole through the middle of the side of it to match your bolt. I machined up a thick walled tube/spacer to go under the head of the bolt so the lathe chuck jaws would grip it. I ended up welding that to the disc and making sure everything ran true.

You put the piston on the disc and put the bolt through the spacer tube then through the hole in the bottom of the disc. Push through the fake gudgeon pin and thread the bolt into it pulling it up tight. That clamps everything together. I could then chuck the whole lot up in my little lathe and know it was central and secure. That worked very well. I used a similar clamping system but with a 45 degree angle plate on the mill to machine flats on the piston crowns (in the Riley 9 they are hemispherical) so the valves don't whack them.

Since then I have wondered if other pistons have that machined step in the bottom of the skirts or is that just some Riley thing?

Simon

[flywheel1935]

Just a thought !!!!, As it unlikely the block has 'warped ' why not just skim the head ??????