Pity about your intake/dizzy gear issue Fred. Hope it's all sorted now.
Mark 4 blocks are old and also used worn tooling later in their production life (so I have read). Their lifter bores were never made that accurate because they never intened to have rollers in them and rollers need to be bang-on.. What makes it worse is already worn lifter bores when used Mark 4 blocks have new rollers fitted into them.
Because of the splayed push-rod design, there is a lot of side loading, so lifter bore wear can be an issue on a well used, standard bore block. Who ever has them checked?
No need to bronze bush as I will simply rebore them accurately to 0.904" and use those +0.062 oversize lifters. Larger lifter diameters are stronger, have more surface area and have a larger roller wheels, axles and bearings, so it's an added advantage. ..and I have plenty of spring pressure to take care of their small increase in weight.
Street driving (lots of idle time) is said to be one of the main, if not -The Main causes of solid roller failure. Not much oil is slung off the crank at sub-1000rpm speeds to keep the rollers lubed -even if you have lifters with pressurized oil feeds to the roller bearings like I have.
Needles bearing rollers are a problem. A bad idea in my opinion and the market is flooded with them. Their is not much collective surface area on those few little needles under the axle. They don't remain nice and evenly spaced around the axle during operation -they bunch up and move around a lot. Any foriegn crud that gets into them will lock them up, or at the least will damage them and their races. They are fragile so any excessive lash or valve float smashes them and pounds them out-of-round, and the roller relies on them to be located on the cam accurately. Proof is their bearings require very frequent rebuilds.
Bronze bushed roller lifters seem to be the only way to go at this stage in history. (Isky's EZ/EZX/EZMax
) They are not the ultimate solution but will eliminate most/all of the above and there is at least one guy on another forum claiming twenty thousand miles of street driving on a set and with a sub-1000rpm idle speed.
With regards to lash, if you find it, there is a reason. Don't just tighten it up and off you go (-like I did.
) If it ain't an easy find like a bent pushrod, it will be the lifters. Pull them.