HILLMAN CAR CLUB
OF SOUTH AUSTRALIA INC

Tech Tips:
Piston Grades
HILLMAN CAR CLUB
OF SOUTH AUSTRALIA INC



From: Ken Shaw [kenshaw(at)cyberone.com.au]
Sent: Wednesday, April 02, 2003 9:41 PM
To: hillman@can-inc.com
Subject: "Hillman " I need help to get started

This message forwarded by the Hillman List.

G'day all

I am sure that this will be the first of many questions to help me build my Hillman engine back to "as new" condition.

I do not comprehend the A.B.C.D. system that Rootes have for an engine description.  I have a Series III medium compression (1494cc No. AA 1970356 MWUO) engine.  Is it A,B,C or D?  How do I tell?

From the front of the engine the pistons have this stamped on the top:
No 1 C @ 12 o'clock L @ 3 o'clock
No 2 B @ 1 o'clock L @ 4 o'clock
No 3 C @ 12 o'clock
No 4 C @ 12 o'clock W @ 9 o'clock

All the pistons have four ring grooves. Does this all mean anything?  If I have to have the cylinders rebored does all the above make any difference?  I thank you now for any help that you may be able to give me.

Regards

Ken Shaw

Canberra
Australia



From: Ed Meadowcroft [ed_meadowcroft(at)snap-tite.com]
Sent: Wednesday, April 02, 2003 10:55 PM
To: Ken Shaw
Cc: Hillman
Subject: Re: "Hillman " I need help to get started

This message forwarded by the Hillman List.

Ken,

Unlike most mass produced engines these had 4 sizes of standard bore piston which were matched precisely to each bore.  The grades were A,B,C and D.  This gave the engines a longer life than say BMC engines before reboring is neccessary.  If your engine is in good shape and you intend to reuse the pistons make sure they are returned to the cylinder they came from.  If you rebore the engine you will only be able to get +.020", .040" etc. and the precisely graded ones will not be available [I don't think they ever were for oversize pistons] so it won't matter.  I presume your pistons have 3 grooves at the top and a 4th one on the skirt.  In early production engines the skirt ring was left out with the recommendation to fit it after a certain mileage but this silly idea was soon abandoned and 4 rings were fitted in the factory.

If you don't rebore it [any idea of the mileage?] I would recommend fitting a set of oil control rings which have a stepped top ring to avoid hitting the wear ridge in the bores and two lowest rings with a ring of spring steel under the ring itself to ensure the rings fit the bores reasonably tightly.  I don't know what the availability of these is nowadays.

Ed



From: Ed Meadowcroft [ed_meadowcroft(at)snap-tite.com]
Sent: Wednesday, April 02, 2003 11:02 PM
To: Ken Shaw
Cc: Hillman
Subject: Re: "Hillman " I need help to get started

This message forwarded by the Hillman List.

Ken,

Forgot to mention, the piston grades do not feature as part of the engine number, they are only marked on the pistons themselves, you have an engine with 3 C grades and a B.

Might have confused you re oversize pistons, they are available [or were] at + .010" thru +.060" at 10 thou intervals.  I've no doubt other list members local to you can advise you of availability.

Ed



From: alkon [alkon(at)bigpond.com]
Sent: Thursday, April 03, 2003 9:17 AM
To: hillmanlist
Subject: Re: "Hillman " I need help to get started

This message forwarded by the Hillman List.

Hi Ken

Others have mentioned the grading system that Rootes used for factory selecting the best fit pistons.  They paid much more attention to detail than many of their contemporary manufacturers, and certainly more than Chrysler ever did.
No wonder the Minx had such a good reputation for reliability  :))

If you are rebuilding the engine the first thing to do is to get everything measured, write it all down.
If the block doesn't require reboring it is absolutely imperitive that every part goes back where it came from.  This includes cam followers, pushrods, rockers, valves, bearing caps (same way round).  Sorry if this sounds a little like telling granny how to suck eggs  :))
If you can get away with replacing stock size pistons, you will need to use a ridge breaker to remove the lip that appears between the top of the top ring and the top of the bore.  Also need to hone the cylinders to remove glaze so that the new rings can bed in.

I have never gone this way.  Mostly the engines I get to rebuild have been abused in some way or other.  So I just bite the bullet and run the boring bar through the bores to the next oversize.  If your machine shop is any good they can bore to suit the pistons you have.  Most cheap engine rebuilders just bore to the nominal oversize and stick the pistons in.  Works most times.  The good motor machinist will only rebore after he has the new pistons in his hand and does the final hone to give the correct running clearance.  Same with the crank, if there is any "ovality"?? in the journals they should be reground to the next undersize.  Again the good guys will check the bearing shells first.
Don't forget the cam bearings, a real pain to replace but often a source of phantom oil pressure loss.

Apart from the machining you can do most of the dissassembly and reassembly yourself.
Cleanleness and attention to detail are best attributes.  Don't rush anything.
It is worthwhile to remove all welsh/frost/core plugs and clean out cooling passages before fitting replacements.  Most engine shops hot tank the whole thing anyway which means the reassembly is all clean parts.

If a new or reground cam is used then new cam followers/lifters will be needed.  Do not try and reuse the old ones; they will just destroy the new cam surface.

I don't know if you have done this stuff before but there are some good general publications available on engine rebuilding and blueprinting.  Petersens had some good ones but they of course are no longer with us.  If you are doing your own assembly you can pay attention to the balancing and blueprinting which are time consuming but give dividends in smoothness and longer engine life.  It is surprising how much engine balancing can be done with a balance or a set of accurate digital scales.
Example all con rods the same weight and the same weight at big and little ends.  All pistons the same weight.  Dynamic balance of crankshaft, flywheel and clutch assembly.  All combustion chambers the same capacity.  I saw an Austin 1500 engine (three main bearings) that would idle smoothly at 150 rpm after being assembled using this sort of attention to detail.  May not make fire breathing power but so smooth  :))

If you do some of the above then you will have your engine better than as new  :))

Keith
55 Californian



From: Jan Eyerman [jan.eyerman(at)usa.net]
Sent: Thursday, April 03, 2003 12:25 AM
To: Ken Shaw; hillman@can-inc.com
Subject: "Hillman " "A", "B" "C" etc

This message forwarded by the Hillman List.

Ken,

The Rootes (hence Hillman) 13901725cc OHV engines were all "selective fit" engines.  They were in essence, hand fitted engines.  It was a cheap way to produce Rolls Royce quality in assembly.

Each engine component was measured and weighed and then marked.  Engines were assembled from matched components.  There were 5 different (I am working from memory so there might have been more) bore "grades" or sizes each one 5/10,000ths of inch bigger.  At that time, the most accurate machining was only to 1 and 5 /1000ths, so a Hillman had roughly an order of magnitude tighter tolerances.

The pistons and rods were also measured and matched and were also installed in matched weighs.  This simplified balancing the rotating parts and actually gave a better balance because each component was balanced rather then just the whole assembly.

Someone has described the procedure as a "blueprinted production engine".

On rebuild, be sure to mark everything and put it back to where it came from!!!  The bore coding is meaningless once the engine is rebored.  It also means that a rebore will never be quite as good as the original.  Same is true of cutting the crank...

Although totally unimportant and meaningless today, Hillman engines absolutely required CAREFUL break-ins.  You could destroy all of the careful assembly work in the first few hundred miles.  That might explain why my '69 Arrow ran as well at 115,000 miles when I sold it as it did when it had 15,000 miles....
I had carefully broken it in.  Too bad they didn't have something to keep the body from rusting away!

Anyway, that is the story behind the letters.  Replacement parts are not letter coded they are just the middle (I think "C").

Since my manuals are not handy, I don't remember where the codes are stamped on the block...

Jan Eyerman


Editor's quote from the Rootes workshop manual for Minx Series I to V, Husky Series I to III and Cob Series I to III
"The cylinder grade letters are stamped on two machined bosses at each end of the cylinder block below the level of the cylinder head on the exhaust manifold side, and visible with the cylinder head in place.  The piston grade is stamped on the top face of each piston."


From: alkon [alkon(at)bigpond.com]
Sent: Thursday, April 03, 2003 9:58 AM
To: hillmanlist
Subject: Re: "Hillman " "A", "B" "C" etc

This message forwarded by the Hillman List.

Measuring to the tighter tolerances is done by operatives with go/ no go gauges.
Semi skilled operatives can achieve quite amazing accuracy by this method.

Jan or some other knowledgeable person has mentioned how Rootes bedded in the engines.  Using a test running engine to rotate the next one for a number of hours to let all the moving bits get accustomed to their place in the world before actually starting it.
We could emulate this procedure quite easily if we desired by mounting a small induction motor in place of the alternator and belt driving the engine (with plugs removed) for several hours.  Best to have oil in the sump and rotate the engine the correct way.  Induction motors typically rotate at about 1500rpm in 50Hz countries.

Running in an engine is perhaps more complex than people realise.  The engine needs to run with a light load, but not no load.  So idling for long periods is not a good idea.  Use medium rpms, probably no more than 3000 and change down early to prevent the engine struggling at low revs.  The reasoning behind this is that the rings need to bed in under some load, if not they form a glaze on the bores and often never bed in properly.  This causes premature oil use.  Do not use friction modifiers (molyslip, STP etc.) during run in.  Often during the run in period the engine will build up heat more than in normal operation, if this happens it is best to stop the car, allow the engine to idle for a few minutes for temperatures to stabilise then shut it down and allow to cool.  When building an engine for sensible street use we assemble using tighter tolerances than the race car or production line engine rebuilders so need to take more time to let it all settle down. Patience is rewarded by a smooth running quiet engine  :))
However fit an aftermarket revcounter so you can see the engine is running  :))

Keith
55 Californian


BACK to Tech Tips index page

HOME page