Rebuilding Austin Healy Sprite Engine No 9C-U-H 619
Assembling the Bottom End
The first thing I did is check the clearance in each bearing. That means all main
and all rod bearings. I used Plastigage do do this, it is a soft material that
looks like a thread. I cut a short length and put it on the bearing, dry.
I then installed, bolted and torqued the cap, whether a main bearing cap or a rod bearing cap. I was careful not to disturb the bearing. As soon as I had torqued the cap I removed it and inspected the plastigage. It had squished and its new width indicated the clearance: the wider the thread, the tighter the clearance. 0.003" in this case. The spec is 0.001" to 0.0025". I decided I would live with what I have.
The plastigage is sold in a thin envelope on which a measuring template is printed. It is available in several
gauges, noted by their color, to accomodate different gaps. (The photo above
shows that red is for gaps of .002" to .006"). I bought mine at the local auto parts store; the clerk initially thougth they did not have any, saying: nobody rebuilds engines anymore !
Once all clearances had been checked, I torqued down all main and rod bearings. Afterwards, I bent up the deformable washers to lock the bolts.
So far, I have installed the crankshaft, the camshaft and the oil pump. I found a good discussion of how to mount the crankshaft saddles here. Below is the crankshaft, installed:
And here are the front plate and the cam gear. Camshaft endfloat is measured only after the camgear has been torqued down, despite the sequence outlined in the Haynes manual. I initially thought I had a problem with the camshaft endfloat and posted a question on the Yahoo bugeye group. I received this authoritative response within an hour ! There is definitely an error in the Haynes manual: the author has the reader check the endfloat before the cam gear is bolted on. Ah well.
The next step was fitting the rings on the pistons, and the pistons in the block.
I initially made a mistake with the rings. I'll describe it in the hope that
it may still be of interest.
Moss Motors sent a set
of rings that have five different kinds of rings, identified as numbers 1,2,3,oil
ring and 5, but the pistons could accomodate only 4 rings (more on this below).
The "oil ring" is actually three parts and could not figure out how to fit it.
Number 5 looked like an oil scraper and I fit it in the bottom groove. No 3
was stepped, with a little "top" on the wide part; I installed that next, with
the top towards the top (D'oh). Next numbers 1 and 2 looked all square and identical,
no markings and no taper. I just put these in the remaining piston grooves.
Here is the result, with one of the old pistons.
Despite looking very carefully, I could not find a mark indicating what is the
front of the pistons, and I could not detect any obvious differences or offsets.
I put the pistons in without consideration for front and back. (Thanks to Alan
for reminding to mention this).
A highly experienced engine rebuilder I have tremendous respect for, who has
rebuilt dozens and dozens of racing engines, once told me that he does not check
ring gap. He says it's always right (I suppose he does check sometimes) or a
little wide, in which case you can't do much. In any event, I checked the gap
for one ring in one cylinder, and got something like 0.013" which is slightly
big. I decided I would live with that. I may yet check more thoroughly, since
it looks like I'm going to have to pull the pistons:
Stop the presses ! It looks like my pistons may actually be some "5 rign"
pistons after all, counting the groove below the pin. I will go and re-investigate
the rings.
A further discussion
of the rings may be found here.
I've broken piston rings before, and I have learned the hard way that the ring
compressor really needs to be tight against the block before pushing the pistons
in.
The pistons are tapped in very easily. Everything is well oiled, of course.
Next will be the timing chain and other parts towards the front, I believe. I will need some help on how to tension the chain and the various kinds of cam gears. I'll post what I find !
here. is a short discussion of
the problem I am facing as regards the cam gear.
Michel Richard
April 3, 2003
Finally, I installed the oil pick-up and strainer. I used a couple of lock wahsers to ensure that all would remain tight.
The bottom end is now complete, and ready to be covered with the oil pan.
Next, I will tackle timing gears and chain.
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