deck height ?

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Simon.Gardiner
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Re: deck height ?

Postby Simon.Gardiner » Tue Feb 07, 2017 9:50 pm

The cases are all the same (I've got a VH mill with NH cases) - but sometimes the barrels get abused!

SG
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)

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Vincent.vanGinneke
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Re: deck height ?

Postby Vincent.vanGinneke » Wed Feb 08, 2017 8:40 am

Hello Ian, I just measured a spare cilinder and the liner raises 4.8mm .
But that height is not really the important bit.
The top of the liner is the seal, this must be slightly heigher then the spigot in the head.
(if you put the head on the barrel you should see light in between them there)
To get a good seal the head should be lapped onto the cilinder. (see Waller)
If the liner is to low you could fabricate a copper gasket (0.8 or 1.0 mm) to get it all o.k.
With regard to the piston ; you could try with a bit of plasticine to check how much room is left between piston and the roof in the combustion chamber.

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Re: deck height ?

Postby Ian.Taylor » Wed Feb 08, 2017 7:49 pm

Thanks for the reply's
Today I measured the and the liner rises 3.5 mm ,inside the head is 3.5mm. So the head sits flush to the cylinder,NO gap.
My VHA with original liner also seals inside the head.
If the liner were to be raised 1 -1.5mm the piston then would be flush
With thick base gasket and the piston almost sitting flush there seems to be a fair amount of clearance inside the chamber.

The inlet drops about 5mm before it hits the valve .I'm not sure how far the VH valve opens

The other solution besides a copper gasket is too have the Liner Pushed out to the correct height of 4.8mm

I've sent Pete Collins an E mail to see if he still makes them
Might better do my 31 as well

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Re: deck height ?

Postby Vincent.vanGinneke » Wed Feb 08, 2017 9:00 pm

I dont think a iron cilinder from the factory has a liner, it's one piece.
Only after the last overbore a liner gets fitted.
So if your cilinder is as per factory there is nothing to push.
Anyway, it's wrong practise to push a liner up as you run the risk of it sinking again...
Fit a thicker base gasket or make up a copper ring for the top (or both).
The top on the cilinder / liner is the seal, not the surrounding area with the four bolt holes.

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Re: deck height ?

Postby Simon.Gardiner » Wed Feb 08, 2017 11:26 pm

I'm not 100% sure but I'd hazard that the valve lift is more than 5mm even with a standard cam and followers (there are several threads with a detailed discussion of valve lift but I can't find one with the figure at the valve for a standard setup just now.)
The '52-'53 iron head VH used a copper gasket that fits on the area around the bolt holes (ie it goes around the flange not on it) and it fits the earlier engines too. That would deal with any sealing issues but probably wouldn't raise the head by enough.

SG
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)

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Re: deck height ?

Postby Leejm » Thu Feb 09, 2017 10:59 am

I believe the standard cam has 8.5 mm lift at the cam, but the lift is reduced by the rockers. If I remember correct I think the rockers reduce the lift at the valve by 1 mm Lee.
1948 NH, BSA D10 SPORTS. 1953 VHA, 1951 KH rigid project.

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Re: deck height ?

Postby Ian.Taylor » Thu Feb 09, 2017 6:05 pm

Back out this morning to have another look.
The piston sits 2mm above the liner.
I then put a very bright light around the 2 mating surfaces and yes I did see some light between the head and Cylinder. I can get .008 gauge in so I know that will seal.

I then re checked the liner height again with a good set of calipers and it reads 4mm not 4.8mm reading Vincent got on his .

I can go with a .032 (.8mm ) ring copper gasket to bring it up to 4.8mm
and add a 1 mm base gasket
If I add the .032 gasket plus the .008 that exist that would make a .040 thou gap between the head and cylinder.
I check my VHA and i can get a .020 gauge in between head and cylinder..Would .040 on the VH be too much of a gap?

Thanks again for the help on this

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Re: deck height ?

Postby Leejm » Thu Feb 09, 2017 6:20 pm

The gap between barrel and head is normally only a few thou. 40 thou is alot!!
1948 NH, BSA D10 SPORTS. 1953 VHA, 1951 KH rigid project.

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Re: deck height ?

Postby Vincent.vanGinneke » Thu Feb 09, 2017 7:26 pm

The size of the gap itself is not very important.
The sealing of the rim in the head is (ofcourse!)

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Re: deck height ?

Postby Ian.Taylor » Fri Feb 10, 2017 1:27 am

On a 39 the gap is 10 & the 47 was .006.So I guess .008 is correct.
What has been sugessted someone may have taken off 2mm from the flange on the barrel for a modification .
I'm just waiting to hear back what the flange thickness is where the base nuts fix to.


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