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TR4/4A Triple to dual exhaust valve spring conversion done wrong?


Jedi Trainee
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While helping a buddy trying to solve an overheating problem on his ’62 TR4 we discovered that the cylinder head had been reworked and converted to 5/16” exhaust valves, bronze valve guides and dual valve springs all around.

The issue we are not sure about is that the DPO’s machine shop used an exhaust valve guide collar (#28) on all the valves, intake and exhaust, and also seems to have used the valve spring set for the triple spring exhaust valve version (minus the small inner spring) and reused the valve spring collar (#30) used for triple exhaust valve springs cylinder heads.

The question is, should my buddy replace the current setup with all new valve spring collars for dual springs and a new dual spring valve spring set and remove the exhaust valve guide collar (#28) from all valves?

As far as I have been able to research qty (4) exhaust valve guide collar (#28) were only used on the exhaust valves using triple springs on TR3s and TR4s engines to CT21470E

Currently the cylinder head is all disassemble and soaking in Evapo-rust to dissolve a breathtaking amount of rust from the cooling passages. So replacing the springs, collars, etc would be trivial.



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Jedi Knight
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A good source for that technical question would be British Parts Northwest. I have found these guys to be accurate about such things. I would add that I converted one TR4 to the same set up. But I had the used parts from a 4A head. I got what other parts I needed from BPN after talking to them.


Obi Wan
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My 4A has a TR4 head, modified with 4A valves and springs, 5/16 stems on both intake and exhaust. It was rebuilt by Dave Anton at APC, who is a high-end engine builder and really should know. It was set up just like a 4A head. So, if it were me, I'd invest in a nice set of 4A springs and other hardware, and just use that.

When I tore down the head, I found that the PO had put the three springs on the intake instead of the exhaust valves. No indication that he suspected something was wrong. I suspect that it didn't affect the intake, but the exhaust valves might have floated a bit at high engine speeds.


Jedi Trainee
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We did some more research and came to the conclusion that the best thing to do would be to set up the cylinder head as the late TR4/TR4A version.
Another friend has a torn down TR4A cylinder head so we were able to compare the hardware between the triple spring and the dual spring versions of cylinder heads.
As it turns out both the spring retainer and inner and outer springs of the TR4A are smaller and lighter.
The TR4A spring retainer is 35% lighter
The outer valve spring is 14% lighter
The inner valve spring is 6% lighter

The particulars (as weighed)
Late TR4,TR4A ; retainer= .65oz/18.4gm ______TR3, early TR4; retainer= .86oz/24.3gm
Late TR4,TR4A ; outer spring= 1.89oz/53.7gm __TR3, early TR4; outer spring= 2.20oz/62.3gm
Late TR4,TR4A ; inner spring= 1.03oz/29.1gm __TR3, early TR4; inner spring= 1.10oz/31.2gm

So currently my buddy is waiting for the cylinder head parts.

On a side note, Evapo-rust did a great job in removing the rust from the cylinder head cooling passages, My buddy is thinking of filling the water jackets in the engine block with Evapo-rust to get the last of the rust out. We already dug out a great amount of rust chunks and sediment from around the cylinder liners, etc. At least now the water runs clean and clear out the front of the cylinder block vs red mud….



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I would suggest the chemicals used in some cleaners is often hydrochloric acid or something similar that would not hurt cast iron, but can damage sheet metal, aluminum and copper. I remember my old machinist buddy using a spring tension gauge that he operated by hand to measure the strength of the springs.


Obi Wan
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Interesting info about the springs. Thanks for the feedback.

As for the block--there might well be a lot of rust around the cylinders, at least that's what I found in tearing down two TR4/4A engines within the past year or so. There was an especially large glob behind the #4 cylinder, where coolant flow is probably lowest. But I'd like to know exactly what is in the evaporust (or anything else) before filling the block with it. Of course, you want to fill only the coolant jacket, not the radiator, water pump, thermostat, or anything like that.



Jedi Trainee
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Thanks for the heads up.
My buddy blanked off the front of the cylinder block and filled the water jackets with the Evapo-rust. The solution turn jet black in a short period of time signaling that it was saturated with rust. Over a period of some hours he drained and changed the solution until there was no visible rust in the water jackets. The Evapo-rust web site does say that it can be used as a engine cooling system flush and that it is safe for all metals, plastics, rubber, etc.

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