8 replies to this topic

[MPea3]

If only there were a Nostalgia/Technical forum! I'm certainly no mechanic, and for that matter no historian, just a fan. I have a question however, that I can't figure out, so this seems like the place to try.

Some of the Millers, and I *think* all of the Offenhausers, used an arrangement where the top end of the engine, cylinders and head, were cast as one piece and then bolted onto the crankcase. First, was this a fairly common practice in racing engines from years ago? Was it more common in engines from another use, such as airplane engines? My guess is that radial engines might use bolt on cylinders, but I don't know if they also use heads as an integral part of that casting. If used in other race engines, when did this fall out of usage, and why?

Second, in looking at drawings for the Offy engine, I can't imagine how machine work was done on such areas as valve seats. For that matter, I don't even understand how you'd get a valve into the guide with the wide angle and length of the valve. Does anyone know anything about this, or can someone recommend a good book which deals more with the technical history of these engines than the personalities and racing history?

Thanks much.

[fines]

The book you NEED is Mark Dees' "Miller Dynasty", it covers EVERY aspect of Miller/Offenhauser.

From memory, yes, all Millers were the same layout. It had the very accommodating aspect of doing away with head gaskets. The valves and camshafts, however, were NOT cast within the block, there was a detachable cam cover to insert and/or service them.

To my knowledge, the Hart 415T was the last F1 engine to use this monoblock technique.

[FLB]

On the same subject, I would recommend Gordon Elliot White's Offenhauser. For Miller background info, you also can't go wrong with Griffith Borgeson's The Golden Age of the American Racing Car.

[dbw]

obviously the miller/offy valves/seats must be accessed up thru the bore....not too difficult if you have the right tools[and know all the tricks]....the single-cam bugattis have vertical valves that also must be installed up the bore...in some late 2.3 blocks the head diameter of the valve is resessed to a size larger than the bore!..the solution was to use screw-in guides..with the larger diameter of the hole left by the threaded guide,one slips the valve in a bit skewed..when seated, the guide is then screwed in from the top and centers the valve stem....[the seats are ground using long extensions]..needless to say,a mere seating of the valves[3X8] in this case can take up a substancial amount of time...i won't even get into adjusting lash....

btw...while the camboxes on both miller and bugatti are detachable,the valves, seats and springs remain in the monobloc....

[VAR1016]

Some of the Bugattis were even more difficult. The type 41 (Royale) and one or two others were cast in one piece: crankcase/block/head so that to grind in a valve, the crankshaft had to be removed i.e. rather than lifting the block from the crankcase and leaving the pistons in situ.

Another engine that used removable valve guides was the straight-8 1.5 litre Delage of 1926/7.

I do wonder how it would be possible to do precision valve-throat work on such engines; I suppose it was much easier to increase the boost from the blowers!

PdeRL

[Peter Morley]

I have something called:

110 Offy Overhaul Manual
written by Harry Striker (P.O. Box 41, Ronald, WA 98940).

It is a ring bound, 61 page, manual for overhauling the 110 Offy. It contains photos & step by step instructions on how to rebuild your Offy.

I'm not sure how much it cost ($50 possibly) since it came with my Offy 110, but was new a year or so ago so you should still be able to find one.

It shows you the special tools, and describes all the procedures.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Monobloc engines (e.g. one piece block and head ) certainly aren't unusual, most Bugattis use them - of course the twin-cam Bugatti was a copy of the Miller/Offy but that was for the cam gear arrangement Bugatti already used monoblocs.

Apparently even quite recent aircraft use them - a (specialised) welder told me that he repaired things like light aircraft engines that had to be welded (cracks between valve seats) from inside the bore.

The F1 HART turbo engine was a monobloc by the mid-80s - I think they started with removable heads, then, as turbo boost increased, moved to a monobloc to get away from head gasket type problems.

[Philip Whiteman]

Not sure about recent light aircraft engines of monobloc construction - certainly some of the great engines from the past were built like this, but the long-established Lycomings and Continentals that dominated the market until the last few years actually had heads that could be removed.

However, the ready supply of complete 'pots' at low cost has reduced the demand on special equipment needed to undo the shrunk-on heads to virtually nil. (People like CSE at Oxford use to separate the alloy heads from the steel barrels in overhauling the American air-cooled engines.)

On the other hand, if you were doing a quick repair job on just one cylinder... (But is it worth it, mother? - last time I asked a complete set of cylinders, complete with pistons, valves, springs and so on, was just £2,400.)

[antonvrs]

Panhard flat twins used this arrangement. I overhauled one once(the infamous Aardvark) and I had to go to the Conze brothers in south Los Angeles and borrow the seat cutters. The pilot went through the valve guide and you reached up through the bore and screwed the cutter on the pilot.
The amazing thing was that Vince Conze, whom I'd never met before, handed me a drawer full of pilots and cutters and said "bring them back when you're finished".
The Brisko six was the same way, IIRC, the guides screwed in to the head/block and had to be removed to allow the valves to come out through the bores.
Tedious, but it worked for a long time in U.S. speedway racing.
Anton

[Henri Greuter]

Another tremendous work about the Offies is:

"Offy America's greatest racing engine" by Ken Walton.
Gives a lot of details about the construction details on the blocks and engines.


Henri Greuter