When fitting new push rod tubes and the after market base gaskets that are 0.75mm. Thick will I have to take that into account when pressing in the new tubes ?
No.
The seals are compressible - by far your more immediate problem is to press in the new tubes without buggering them. When I did mine the seller of the stainless steel tubes I bought suggested purchasing an extra one as a spare against "accidents".
I didn't need it, but I can perhaps give you some tips to avoid you ending up in pain.
First, using a few bits of timber, make a fixture that will support the head such that the bores into which the pushrod tubes will go are as near to vertical as possible. If you are lucky enough to have a vice big enough to hold the fixture, great, otherwise some adjustable clamps will suffice. The advantage of the vice is that you can see the bottom of the bores and can therefore more easily judge when to stop.
Next, using a very fine sandpaper and kerosense (or steel wool if you prefer) clean the pushrod tube bores to remove any "roughness", go careful and do not use anything that is going to increase the bore diameter, clean and bright is the target - do not remove the "ledge" that resulted the last time pushrod tubes were driven in, this is your witness mark to ensure that your new tubes are seated far enough.
Puts heads in oven at 220 degrees centigrade for about 30 minutes, put pushrod tubes in freezer for about the same length of time after first smearing the thinnest possible amount of something with some lubricity on the ends that are going into the heads, I used a light silicon grease that I normally use on bicycles - be sparing.
Next, remove your rear axle, this just happens to be the perfect size to use as a driver to drive the pushrod tubes in - alternatively, turn a suitable length of bright mild down in a lathe and use that. Whichever you use - put it in freezer with the pushrod tubes.
Remove heads from oven, mount on your fixture. Remove axle and the lucky first pushrod tube from freezer. Hold pushrod tube over the bore you select with axle (or your own home made driver) inserted and gently start it into the bore. Then grasp your 5lb hammer and smite the end of your axle - adjust next blow in accordance with how far it moved on the first one. You will probably know when the tube reaches the "ledge' if not, look carefully after each smiteing. Don't go too far cause backing it out is a bastard.
If you succeed, put axle back in feezer for 15 minutes and do the next one. If you crumple or bend the pushrod tube - go and do something else, today is not your day to be driving pushrod tubes.
Do note stress too much about being overly accurate with the exposed length of pushrod tube, within reasonable limits the seal will crush down to accommodate minor inaccuracy.
Now, I am pretty sure that freezing will work I just happened to have a liquid delivery LPG cylinder and gave the tube I was about to drive and the axle a bath in rapidly boiling LPG in a piece of plastic downpipe - they were very cold.
You really only have a few seconds to get the tube home as it is very thing and heat transfers from the head very quickly, although the cold axle does slow this down a bit.
Lots of luck
Tony Smith
Remove head from oven, set in fixture - i
