850 Valve interference on the Piston.

AZScott said:

Appreciate all the comments, thank you. My timing off one link appears to be the problem. It was mentioned in the posts that Cylinder Barrel Spacer might be available. With 40 plus years on the head and barrel, and not knowing how many times it was re-surfaced, I thought I would like to see if one is available for a 850 I can find one listed for a 750 "Cylinder Barrel Decompression Spacer Norton 750 Combat Commando S189" , but have not found one for a 850. Does anyone know is one is available, and who carries it?

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Check out JS motorsport web site, Jim does copper barrel gaskets that can space things out if required plus a host of different head gasket options.
BUT before sticking anything extra in there, I'd advise a simple check of filling the combustion chamber with oil to determine your current situation.
Its easy to do: set at TDC on compression stroke, measure how much oil it takes to fill, this is your combustion chamber volume, add this to swept volume of one cylinder and then divide the total by the combustion chamber volume and you get your static compression ratio. Compare this to what your bike had as stock and you can ascertain if much has been hacked off of head or block.

AZScott said:

Appreciate all the comments, thank you. My timing off one link appears to be the problem. It was mentioned in the posts that Cylinder Barrel Spacer might be available. With 40 plus years on the head and barrel, and not knowing how many times it was re-surfaced, I thought I would like to see if one is available for a 850 I can find one listed for a 750 "Cylinder Barrel Decompression Spacer Norton 750 Combat Commando S189" , but have not found one for a 850. Does anyone know is one is available, and who carries it?

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JSEngineering just supplied me a 0.5mm copper barrel gasket for my 750. The old paper gasket I removed measured 0.5mm so I replaced it with the same thickness paper gasket. The new paper gasket was extruded from the joint and on removal was 0.38mm thick (they don't make them like they used too). Copper for me from now on.
I don't know about 850s, but with 750 engine insitu, I lifted the barrels until the skirts cleared the studs, annealed and painted the copper gasket, cut it at the rear, fed it in around the conrods, apllied a smear of sealer at the cut then screwed it down. Precaution: 1. Start with pistons at TDC so you don't pull them out of the cylinders, 2. As you lift the barrels, you must lift and secure the rockers to keep the pushrods in place.
Hope this helps.
Ta.

Cam timing is 2 links out according to the picture. You possibly haven't bent your valves but you are best to check them.
Dereck

kerinorton said:

Cam timing is 2 links out according to the picture. You possibly haven't bent your valves but you are best to check them.
Dereck

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I count one roller out. It should be 10 rollers (5 plates) and I see 9 rollers (4.5plates).
Compression test will assess valve seating.
Ta.

needing said:

kerinorton said:

Cam timing is 2 links out according to the picture. You possibly haven't bent your valves but you are best to check them.
Dereck

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I count one roller out. It should be 10 rollers (5 plates) and I see 9 rollers (4.5plates).
Compression test will assess valve seating.
Ta.

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Your right. the 2 white dots fooled me. They should be in the middle of the corresponding side plates, but one plate further apart than shown..

AZScott said:

found the intake valves were nicking the pistons on both sides.

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I have bent a valve on a Honda motor with less of a witness mark than what you have. Double check compression before you run it.

Cheers

AZScott said:

found the intake valves were nicking the pistons on both sides.

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The only proper thing to do is remove the valves that had contact with the pistons and check them for straightness in a collet lathe (or in vee blocks) with a dial indicator. A bent valve may not show through a compression test.

Since you shaved the head (and may or may not know the full providence and history of the engine) I strongly suggest you clay the piston tops once you sort out the timing in order to confirm piston to valve clearance. You are already there so.......might as well do it.

Dances with Shrapnel said:

AZScott said:

found the intake valves were nicking the pistons on both sides.

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The only proper thing to do is remove the valves that had contact with the pistons and check them for straightness in a collet lathe (or in vee blocks) with a dial indicator. A bent valve may not show through a compression test.

Since you shaved the head (and may or may not know the full providence and history of the engine) I strongly suggest you clay the piston tops once you sort out the timing in order to confirm piston to valve clearance. You are already there so.......might as well do it.

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I am sure that is th eproper way to check the valves for straightness.....and I certanly agree the OP should do a physical check for clearance when reassembled even if it unlikely to be an issue when the timing is set correctly.

But a more rough and ready check of the valves can be done by simply removing the springs and checking free movement of the valves in and out of the guides, rotating the valves while repeating.... Then just use a little fine grinding past on teh valve and lightly grind....it should show any anomolies, especially if you now they were goodbefore initial assembly....