(See “Name that engine” competition at the end, with fabulous prizes!)

H-D stepped up to the plate with an OHV top end to go on its D-model 45’s, and these were given the designation DAH.  It used twin-port exhausts, as on the Koslo.  Twin ports for a single exhaust valve was a fashionable configuration on British single-cylinder sports models of the era, and all the major British factories offered their sports models in both twin-pipe and single-pipe options.  Flash-Harry’s who gloried in lots of chrome went for the former, serious riders went for the latter. 

Apparently even fewer of these DAH’s were made than the Indian OHV.  A couple were used for hillclimbing and at least one was made into a prototype streetable version.  The official word was that this was for European road-racing, but Alan Girdler (“Indian and Harley Wars”) suspects that H-D may have been contemplating a major switch to OHV for its road bikes at least a decade before they eventually did.

And do I like the H-D effort?  Well, no.  Indian’s OHV is a much more handsome hunk of metal.  The picture of the streetable version did bring me around to the idea of twin-ports for the Koslo heads, however.   It would be magic to have  Chief cases fitted with Koslo heads, with high-level pipes running together down both sides of the bike like double-barrelled shotguns!

It would be remiss of me to leave any discussion of fitting OHV topends onto Yank-twin cases without mentioning the heroic efforts of Bert Munro, who legend says used to carve his conrods out of titanium using nothing more than a blunt bread-&-butter knife.  Well, not quite, but almost.  The winter nights are long down there in Invercargill, and there was never anything much on TV in those days …. in fact, they didn’t have TV in those days.  Anyway, he built the world’s fastest Indian, and here’s its engine.

Of course, anyone making an OHV design in the ‘20s would first have had to take a hard look at the JAP engines made in Tottenham, London, which were the industry standard in those days.  In the early ‘20s, Val Page designed a 500-cc single that got used in grasstrack and later speedway, where it dominated that sport for years.  The JAP-V-twins were based upon this top-end, and were used as proprietary engines by Brough Superior, Zenith, OEC, NUT, Coventry-Eagle, Morgan, and so on. 

These JAP engines use through-bolts from cases to heads, rather than cylinder base studs.  Rocky is giving serious thought to making the Koslo top-ends in a similar fashion, and certainly it will give a more sturdy engine.  There’s two ways to do it, though.  One is to cast four grooves in the finning to run the studs in.  The other way is to keep the circumference of the fins intact, and run the studs up through holes cast or drilled in the finning.  The latter looks much nicer, and can’t be too big a deal to manufacture since a host of British factories made their cylinders in this way.

Another issue with the Koslo heads is whether or not to retain the twin-port configuration.  Most British factories offered both as options, and serious tuners preferred single-port heads.  However if the idea is to offer faithful reproductions of Koslo heads then twin-port is the way to go as this is “authentic” and the patterns do not have to be re-worked.  If single-port Koslo’s were ever to be contemplated, then one could look at the Sunbeam Model 8 shown here, as it has the same head finning pattern as the Koslo heads.

Also shown here is a 500-cc Sunbeam, and I show it simply because it’s a very pretty bike.  When John Marston still owned the Sunbeam factory, it was justifiably famous for the quality of finish on its bikes, and for the cast-alloy oil-bath chaincases (years ahead of their time).  This bike represents Sunbeam at their pinnacle.  The rocker gear looks nice, too.

Next up is a Norton CS1, which was an overhead-cam pioneer of the ‘20s.  I slip it in here just as another example of how through-studs can be designed into any cylinders that get made for a modern-day replica Indian OHV conversion.  Also shown is a Dunelt Vulture, and quite why they called it that is anybody’s guess.  The engine is a famous one, though.  It was made by Raleigh for fitment to their own bikes, but also supplied under their Sturmey-Archer trademark to anyone else who wanted to sell motorbikes but couldn’t be bothered making engines.

I’ve had my own fantasies in years past of a Chief bottom end with Ariel Red Hunter 500-cc top-ends put on it (see Chopper Column Part 5), because these parts can still be bought and because they have  valve gear enclosed inside rocker boxes.  The various designs shown above have almost all got exposed rocker gear – in fact many of them look like side-valve heads that just had valves shoved in through the roof like birthday candles, with the means to actuate them simply bolted on top.  Which is presumably how the transition from SV to OHV got made.

You can see from these Ariel pictures how this engine, designed by Val Page as his next project after he’d finished the JAP engines, further made a transition from exposed valve gear to enclosed rockerboxes, which became the UK industry standard by about 1938.  Check out the gorgeous high-level pipes on the sports model shown!

So what’s the appeal of slapping OHV onto one’s Indian?  Moen quite rightly asks “How fast do you wanna go?”, and points out that Rick Abbott’s 101 is already frighteningly quick in “humble” sidevalve configuration.  OHV will just add expense and a higher centre of gravity.

Well, speed probably doesn’t even come into it.  Neither does logic.  I can think of two main reasons to want an OHV conversion, both illogical but no less valid for all that.

On the one hand, there’s people who might want to faithfully reproduce a rare and glamorous model from Indian competition history.  That’s if it’s possible to “faithfully” reproduce any racer, considering that the words “stock racer” were simply never in anyones’ vocabulary.  Not if they liked winning, that is.  Still, a reproduction OHV Indian will be rare and interesting.  Might even be a winner, too (would they be eligible to race?)

On the other hand, OHV conversions are great for people who just like the look, sound and character of such engines, who were raised in an OHV world and for whom the idea of sidevalves in a motorcycle engine still takes a bit of getting used to.  It adds another dimension to the Warpath concept.

While I’ve always myself wanted a non-Harley OHV V-twin, I had never until now considered using this exposed type of rocker gear.  I suppose we all have in our own mind a limit of practicality, or a point of time in motorcycle design, beyond which we don’t want to go any further back.  I mean, go too far back, and I’ll wind up sitting on a bicycle!  The cut-off point for me had been the mid-thirties, when motorcycles all acquired saddle gas-tanks, OHV with enclosed valves, and re-circulating oiling systems. 

Rocky’s Koslo article has therefore been an eye-opener for me, because it’s caused me to appreciate  the exposed valve gear OHV designs of the ‘20s.  I can now appreciate that they most likely work quite well, as long as one is handy with a grease gun, and setting valve clearances will be a doddle compared to my Triumph 650 or (shudder!)  the “modern and convenient” Honda CB550 Four I used to own.

I can also appreciate that they look down-right funky, with all their works on display and going “clickety-clack-clickety-clack”. 

This is what antique biking is all about!

(more below)

What might have been.  Prototype streetable DAH.  Love the pipes!

New Zealand’s take on the OHV Scout concept, the record-breaking Munro Special.

Anyone making OHV in the 20’s had to first look at this engine, the venerable JAP OHV here in 1000-cc V-twin guise.

Brough Superior used JAP motors, and this view shows the through-bolt cylinder stud construction, with studs running up through drillings in the fins to the heads.  Very sturdy.

Here’s a cute little 680-cc model Brough.  Note the single rocker-mounting lug on the heads holding the rocker shaft in the middle, rather than at its ends.  A neat and tidy motor – very attractive.

JAP cylinders, showing grooves in the finning for the pushrods, but not for the cylinder through-studs – these run up through drillings in the fins to give a much neater appearance.

This Sunbeam 350-cc Model 8 has the same cylinder-head finning pattern as the Koslo heads. Kolso patterns could be re-worked to lose one exhaust port, and have the finning extended (like this) over the area where the extra port used to be.

Sunbeam’s 500-cc Model 9, their top-of-the-line sports model.

The appearance of the rocker gear is rather nice.

Another British bike, this time a Norton CS1 OHC, showing how through-studs can be run inside the cylinder finning rather than have trenches in the fins to accommodate them.

The name of this bike, made by Dunlop and Elliot,  is the “Dunelt Vulture”.  No wonder it didn’t sell!

Post-1938 Ariels with enclosed valve-gear, and gorgeous high-level pipes on a twin-port option bike.  Imagine a Chief with Koslo heads and pipes like these!