Hi Y'all,

More of a discussion topic (and some learning for me) than a specific technical question, but...

Of the traditional engine, pre-unit, 4 speed bullets which I understand were manufactured between the 60s and the early 2000s, what (if any) distinguishing features do the engines have? Either external/visual differences and/or internal differences that could date the bike/engine? Obviously engine numbers/VINs will give it away, but that's no fun. And I'm not really interested in body work, accessories or colours...for context...

I've recently finished building this 500, 4 speed, pre-unit...and not much of the stock bike is left. I am thinking about seeing if I can race it in my clubs vintage class next year. The class doesn't have a defined "cut off date" for the age of bikes, but rather a "spirit of the class" rule that is determined by some of the organisers. The age of my motor might not class it as "vintage" but the technology sure would! So I am just interested in the actual differences in the motors from the 60's, 70's, 80's, 90's, etc. I'm not trying to deceive my club or anything, I'd be straight with them if I ever entered.

Just wondering how much of an RE expert you'd need to be to tell the difference between different years of the same model...can anyone date my bike from looking at it???

Looking forward to hearing folk's thoughts,
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Where do you begin? I assume you're talking about the Indian-built Bullet engines, the UK Bullets ceased production around 1961.

The Indian factory didn't produce a 500 engine until 1989/90, 350s only until then. The 500 has extra angular finning around the exhaust port for quick reference. Pre 1978 the Indian Bullets would also have had an English Bullet type pressure release valve on the front of the crankcase under the oil feed pipe to the rockers, as well as (less obviously) imperial instead of metric crankshaft main bearings. Pre '78 the timing gears were also used for the oil return to the tank from the timing chest, the crankcase and the timing covers on the inside are like gear pump housings. Late timing covers have the tab cast in to assist removal by clouting with a piece of wood from behind the engine, instead of leaving owners to try and pry the thing off with a screwdriver and possibly damage the joint faces.

There are chassis differences too over the years.

The crankcase breather stub on "original" bullets is a seperate bolt-on casting. The indian ones have it cast into the crankcase. Later ones have the stub with no hole in. Very late ones don't even have the stub.

Your bike has a full-width, twin-leading hub on the front wheel. Pretty sure older ones either had a half-width or double sided front brake.
Not sure, but I think the earlier Indian 500 Bullets had 2" carburetor stud centres until about 1997 then they went to 58-60mm(?), the 350 stuck with 2". Also can't remember what year the PAV started being fitted to the exhaust pipes.

While on the subject of running gear, the pre-1988 forks had separate screw-on oil seal holders like the UK-made RE items, but have we missed any differences regarding the engine? This was the original question. You could add increasing use of metric fasteners, not immediately obvious.

The crankcase breather is the most obvious external guide to possible year of a Bullet engine

Redditch Bullet:
350cc (1949-50) - breather on primary Chaincase - push-in tube on early / banjo fitting on bottom late-
350cc (1951-55) - banjo fitting at top rear face of left half
500cc (1953-63) - 3-screw breather set into stub fin area below cylinder on left side
350cc (1956-63) - shares the 500's wider crankcase casting (machined to suit of course) so has the same breather unit.

Indian Bullet:
Originally supplied to Madras in kit form from Redditch as the Bullet CKD
350cc (1956-75) - 3-screw breather set into stub fin area- metric bearings in engine from mid '72 on
350cc (1976- 89) - cast in breather set into stub fin area
350 & 500cc (1990 -96) - cast in breather with no stub fins
350 & 500cc (1997-03) - cast in breather with raised pad below for engine number
350 & 500cc (2004) - breather behind cylinder from top of oil compartment - cast one initially sealed and then removed
350 & 500 cc (2005 to finish) - breather from top of oil compartment

Note that any 350cc crankcase with the 3-screw breather can be re-machined to take a 500cc top end.
I am not sure if the same applies to later Indian crankcases
My 2004, Indian home market, 350 Bullet Electra has crankcases stamped "C4 & 500". I assume this means they are the same as a 500, but not sure. There is no crankcase breather on the upper left side crankcase; there is only a single outlet from the top of the oil tank.

I have considered fitting the Hitchcock's extended oil filler with a breather fitted to the rear face of the timing case, where the distributor would normally go. However, I don't have enough information to work out if this is worth doing, or possibly even counter productive. I've just emptied the breather/oil separator/catch tank and as usual, there was a fair amount of watery oil "mayo"/ gloop in it.

I noted, with interest, Michael Waller's video where he described how the dizzy drive idler gears fit in a recess by the return aperture and to help pump oil from the timing chest back to the tank. My bike obviously doesn't do this because it has no distributor or idler pinions. It might be that blow-by gas pressure in the timing case helps push oil back to the tank and fitting an extra breather might upset this.

Oops, sorry for the thread drift!
Adrian, yes I understand that. I looked at the innards of my engine when I carried out a top end overhaul and noticed various internal vent holes. I’ve also studied the diagrams in my workshop manual, which tbh didn’t shed much light! However, unlike all the other bike and car engines I’ve worked on over the years, I was surprised that the Bullet appears to have no breather outlet in the rocker cover. As far as I can see, the only way for any pressure above atmospheric in there to vent is down via the timing case and from there to the oil tank and it’s breather, the latter being the the only outlet in this version of the engine.

If the pressure in timing case is higher than that in the oil reservoir, which is open to atmosphere, it must have some effect, even if very minor. Venting the timing case would equalise the pressure and then gravity would be working alone. I have noticed that there is a significant drop in the oil level in the tank after running the engine for a few minutes, even from the full mark on the dipstick and when I’ve done oil changes there’s a great deal of oil sitting in the timing case. Being more used to other perhaps more conventional types of oil system, this seems a bit strange.

It seems that the venting system was significantly altered over the years yet the basic engine design remained the same. The early engines with a magneto obviously had no space for a vent on the top face of the oil reservoir but they did have a crankcase breather on the left side. My bike doesn’t have the latter so any pressure build up must dissipate by other means. I don’t know if my engine’s crankcase vents on the right directly into the timing case, but I suppose it might.
If there's no functioning breather stub on the left hand side of the crankcase, then the crankcase will vent directly into the oil tank, somewhere near the top, of course. Our hosts' filler neck extension/breather tower thingy won't be a lot of use with this design, it is more intended for the older breather type of engine, effectively using the oil tank as the breather catch-can.

I have a spare set of 350 Electra crankcases which I can check if you need.


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