Thread: Difference between Spreadbore & Siamese

Thanks Keith,

You can see why they crack between the two pots not much meat there. I had a look at one over here a few days ago with hair line cracks betwen the pots. Can you show us a pick of the head surface . I could not iunderstand why one head fits all until you explained they are dead flat. No machining in the head.
Mike

Does the position of the valve in the head vary in relation to the center of the cylinder?

As you've pointed out the siamese bore are closer together than the spread bore, basically because the centre of the bore in in the same location as the centre of the bore is the 1595 cc engine.

The other issues: The spread bore also have a full flow oil filter system instead of the bypass oil filter. On the siamese bore, the crank has a reverse archemedes screw as a oil retaining mechanism on the rear of the crank, while the spread bore has an oil seal. (There was an Australian retrofit where the screw was ground off the crank and a rope seal device fitted.)
The simese bore had integral thrust washers on the middle main bearing while the spread bore had individual thrust washers and bearing shells.

As for the exhaust valves, the cam and cam followers are the same on both engines, as are the head.

Originally Posted by slug_burner

Does the position of the valve in the head vary in relation to the center of the cylinder?

The same head fits all so as the centre of the cylinder of the spreadbore is not the same as the centre of the siamese then the valve position would alter very slightly.

OK another one. Lets say you have an 80" or an 86" with the engine that has the remote bypass filter in front of the starter motor. You cant find or read the engine number so is it a 1600 or a 2 litre siamese as they look pretty much the same externally.
Put your hand between the block and the firewall,. The siamese has a blanking plate with two bolts over a cast opening in the block at the end of the water jacket.
The 1600 does not.

Originally Posted by 123rover50

The same head fits all so as the centre of the cylinder of the spreadbore is not the same as the centre of the siamese then the valve position would alter very slightly.

The head is flat and the inlet valve uses the extension of the bore cavity for the exhaust valve. So while the bores 1-2 & 3-4 have moved apart slightly it has no impact on the position of the valves.

Hi

Another difference is the use of the copper backed big end/main bearings in the spread bore engine . The oil filter was changed to accomodate the copper backed bearings .

Copper backed engine bearings were the latest innovation in the auto industry in the mid 1950's , so I believe

And, there is a difference in the coolant distribution tubes in the block.... cannot rememebr which is which right now

Mike

In the cylinders of the 2 ltr siamese bore, I have found the chrome plating caused problems with the rings sealing.
Was chroming done in many of those engines?
.