Hi Terry,This is very interesting! Could you explain some details about your technique, please.
Sorry, I just dropped a couple of pictures in a ‘what we have been up to’ thread, and I did not think to make a technical post in it.
I can add some text though, But please treat it as a ‘what I did’ rather than a ‘How to’.
There was a weep from a pushrod tube seal, so it was time to replace the seals- the plan was not to get too involved in the engine, just replace the seals and pop the head back on. But found a suspicious dark area on the land between the cylinders, checked the head with a straight edge and found I could slip a 3 thou feeler gauge between the head and straight edge.
I cleaned the head, removed the valves and heated it in my garage oven for a couple of hours, at 175 degrees C.
I turned down the end of a nylon bar to fit between the vertical fins of the Head, so hopefully I could press with minimal risk of damage.
View attachment 731427
I placed two bars across the head in line with the outer bolt holes, to support the outside only while I pressed the middle down. I then placed a plastic board on the bars, the idea was that the plastic board would protect the head from the steel bars, but would flex during the pressing process.
View attachment 731428
The board is a strange shape because it is really my piston support board used for fitting cylinders. You can see where the head has pressed into the plastic (on the board and the nylon bar).
I used a combination of pressure gauge and dial gauge (dti) to monitor the forces and a ‘laser’ temperature gun to monitor the temperature.
Then it was just press a little, remove from the press and check the bow, monitor temperature .
Refit into press, press a little harder, remove and check.
When the temperature got to 150 degrees C, reheat.
As soon as there was an improvement and the head did not spring all the way back to 3 thou bow, I set the pressure to the last used reading and zeroed the dial gauge. When I pressed 0.00175" the head sprang back 0.00075" so I got 1 thou of straightening for 1.75 thou of pressing.
I just kept repeating, checking and gradually increasing the pressure until the head was flat.
I placed the head back in the press under a little bit of pressure while it cooled.
Things still to do:
The valve guides are in good condition so I am not looking to replace them if I can help it.
I will check the valve guide to seat alignment in case the heating and pressing have distorted anything, if it is reasonable I will touch the seats in with a light hand grind/polish.
If there is a problem with valve alignment I will have to have the valve guides professionally replaced, as I cannot replace them successfully successfully at home.
Hi Peg, I would say you're a lot more than an amateur bodger, with a technique worked out like that.Hi Slofut,
No I’m just an amateur bodger.
I just don’t post the stuff that goes badly wrong😊
Hi Terry,Hi Peg, I would say you're a lot more than an amateur bodger, with a technique worked out like that.
How did you arrive at the (I assume ) stress relieving parameters that you used?