Having liberated a '74 Strada from its incarceration in a not-entirely-weatherproof shed of a friend, the boxes of bits that came along with the nearly rolling chassis were duly investigated. Nestling therein was an almost complete Sport spec engine fully dismantled, but wrapped up well for its storage of about 25 years.
Some parts were corroded beyond use so I kept a weather eye on a certain well known auction site and was rewarded when I was able to purchase another engine in boxes which was an almost complete Kangaru spec engine fully dismantled and rattling around unloved having had the plain main bearing fail due to lack of lubrication.
As the intention was to have one good engine, all parts were duly examined and with my learning curve heading upwards rapidly started to realise that it was not all as straightforward as one might have hoped...
The cranks were different shapes and weight, although both having a plain main bearing, the K crank had been ground undersize on both the big end and the main, whereas the S one was standard, but worn on the big end such that a grind was required. Measuring the K big end, which looked good, and with new shells fitted, the clearance was 0.07mm which is on the high side according to t'blue book.
As the oil is asked to lubricate the plain main bearing after it has performed similar duties to the big ends and has to travel against centrifugal force in order to do so, having the smallest clearance at the big end seems to be the way to go. The lack of fillet radii on the big end also led me to suspect that the regrind had not been done with sufficient skill.
The barrels were different too, the S engine had worn liners and split skirt pistons, as opposed to the K engine with nicasil coating (or similar) with solid skirt pistons (corroded and scored).
The crankcases were better on the K engine as there were chunks off alloy missing around the sprocket area on the S. Chain snapped I guess...
Following multiple bearing removal, cleaning and aquablasting of the cases and parts to be used, new bearings of the correct C3 spec were fitted along with new seals from those nice people at NLM.
Using the info from the blue book and a yellow factory type manual, the gear cluster was assembled and fitted into the casings and checked for endfloat, which it had to much of, i.e 0.6mm. However there was no mention of a limit in either book so I can only suspect that the output shaft is not shimmed, also the washers available are all 1mm thick. Whilst setting the gearchange, the endfloat on the output shaft did not help, so I am going to reduce the clearance to about 0.1mm with a specially ground shim.
The heads were stripped and blasted and new guides were obtained from NLM, but oversize was all that was available so they were turned down to suit and duly knocked into the pre-heated heads. The new guides are bronze whereas the old original ones were steel or cast iron. The exhaust threads seemed OK on the K engine so they were the ones chosen for this build.
The cams were different as well... The S had a cam marked with and S (suprisingly
) and the K had no markings, but measurements showed lower lift and less duration. You can guess which one I will be using, I'm sure.That about brings me up to date as to where I am, the crank has to be ground on the big end, and the same people will sort out the heads getting the valve seats recut and their faces ground.
The chassis will be the subject of a later post.
Cheers
A