Hull, East Riding of Yorkshire, England
Joined: September 2020
Chaps, new member here. Located in Austin, Texas.
Looking for advice on a new project.
I just bought a 'barn find' 1972 A65 for $1250. Was last registered for road use in 1981.
Wiring is completely fried. Burnt. Gone. Melted. Take your pick.. Previous owner has passed
away and I bought it from the estate sale. It's rusted to heck. Need to replace most of the
bright work, but that's not so hard.
I plan on rebuilding the engine around a large journal A10 crank and a big bore kit from E&V.
The A10 giving me an 84mm stroke and the E&V kit gives (according to the web site) an 80mm
bore, so 845cc. I am looking for advice on this aspect of the rebuild, specifically carbs, cams,
head work and gearing. I have browsed through the forums but much of the discussion about
such a conversion seems to be for high speed work. I am not looking for that..
This is going to be a rider, for the times when 'her indoors' has taken the car. I am not looking
for land speed records, but more low end and mid range. Given it's an A10 crank, an rpm limit of
6000rpm seems sensible. That said, most of the driving speeds where I live are pretty brisk. 65mph
on most of the normal roads just to keep up with traffic. 75 to 85 (yes, 85 is legal in places)
on the interstate/toll roads.
The E&V bore of 80mm seems a lot given the center head bolt. My memory of my last A65 ('69
Lightning back in 1974, left big end seized, broke the rod and poked a hole in the crankcase
while coming down the hill on the M2 from Maidstone to Strood) was that there wasn't a lot of
meat to seal the head gasket in that area.
Requested advice point 1 - I am looking for experience with that kit or direction to the SRM
Speaking of SRM, I plan on using their oil pump and other gubbins, but the conversion of the crank
to their end feed bearing would be pretty expensive, involving the transatlantic shipment of cases
and crank. Instead, I plan to get a custom bearing made up that's A65 on the outside and A10 on the
inside, after getting the crank crack checked and appropriately ground. I plan on using the stock rods.
In-line bore the main bush to size, indicating X-Y off the drive side main.
The engine on the bike is stamped as an August '72 A65T but it has a rev counter and a twin carb head.
Registered in the USA in February 1973.
The head is not original to the bike and has a casting number of 68-701. I am surprised at that, I would
have expected 68-704. However, the '71 and up head steady is missing and the rocker box cover matches
the head and doesn't have the 2 tapped holes for said head steady. The head has the bolt hole for the
previous head steady, but nothing on the OIF frame to bolt it too.
Anyway, let's not obsess about the head steady.
The inlet ports on the 68-701 head are as straight as an arrow and 28mm in diameter. Clearly, new valves,
springs and guides - but given my intended use - flow the 28mm ports? Can't hurt.
Requested advice point 2 - Open the ports to, say 32mm and use 2x Mk 1 32mm Concentrics from a Norton 850
Commando (with same jetting)? I tend to think that this would only help high end RPM, which isn't my goal.
The 28mm ports will keep the air flow pretty speedy and help with low to mid range, which is what I am
looking for. I understand that keeping the 28mm ports might limit top end, but that's okay. If I keep
the 28mm inlets, I would plan on using similar jetting to a 750 Bonneville, but a slightly larger main jet.
Looking for direction there.
Requested advice point 3 - Camshaft. I was going to use the stock Spitfire can. but maybe advance it a little.
I see that MegaCycle advertise cams that improve low to mid range on an A65. Has anyone experience of those
Requested advice point 4 - Gearing - My memory of my previous A65L which had 20/47 gearbox to back wheel, was
that 70mph was over 4000rpm. I want to drop that down somewhat. A 22 tooth gearbox sprocket is easy to find.
Maybe dropping one or two teeth on the back wheel? The rear wheel sprocket might be a problem as the securing
bolt heads are close to the chain. My calculator says that 22/45 give me about 3800 rpm for 70mph. Any
Thanks for reading.. It's a long first post !
The better way is to use a norton 750 commando crank and turn up a flywheel
preferably at 90 degs offset. It's a fair bit more machining work though.
The A10 crank is not as strong as the standard a65 crank that's why beeza's
made a different crank for the a70.
Nourish used to make an 85mm crank for the a65 that would be an excellent option.
30mm carbs will be fine for the road. Standard 'spitfire' cam.
Stick the whole lot in a box and get E&V to quote for the job.
You'll be up for:
End feed conversion
Oil pump overhaul
7 plate Clutch
Refurb the carbs.
Cylinder head ('71+ type)
Cylinder head overhaul including valves, guides, springs etc.
Gearbox outrigger bearing and plate
Kevin on the triumph section of this site listed a bloke who has some nice
84mm cranks done for a65's can't remember his name though. Nice job
but not a budget item.
Go out and buy a late Moto-Guzzi it'll be cheaper!
And bye the way Gavin, when fitting a different crank, yes a needle race is the way to go,
i just don't think it's required with the standard engine.
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I'm not sure you want to go with the 22t G/B sprocket. I'm running a 21t on my 845 and put a 50t rear (could have used a 20t G/B, but was to lazy to strip the clutch off) to make it a little better at low revs in 1st. and it still does 80 at 5k rpm. Although my primary gearing is a little higher and running a 5 speed gearbox so its not the standard std set-up.
Using an 84mm crank and B44 pistons will make the barrel base to head height more or less the same height as a std 650 height. If your 72 cam is Ok, just use it, unless of course you go 90 degree.
The fact that you need a late type head in order to get the correct rocker cover to give you a head steady is good. and gets you away for this 28mm inlet. You are adding 100 cc/ cylinder you need to let that engine breath, sorry to disagree with all the small port gurus, Go look at some off Mark Parkers posts on porting. If you want to email me at [email protected]
I'll send you a spread sheet on the ratios you can play with.
my tuppence worth
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|by gavin eisler|
On cam choice , gearing and revs.
My 732 big bore has the 21 tooth sprocket 47 rear, and stock late "Spitfire " cam timing, the motor starts coming on the cam and puling hard from around 3.5 K, I wouldnt want gearing that put my cruise speed below these revs. For a super soft motor you could put in the pre 66 cam for less top end more mids, combined with flat top pistons, stock valves and a single carb this would give a nice smooth stump puller but it would lose a bit of sparkle at higher revs.
I often find my self changing up when I am already in top, but I know if I fitted taller gearing I would lose on acceleration and hit a brick wall of wind at higher speeds, 21 47 is a good compromise for me.
The 732 has a load more middrange than a stock 650. For a fun smooth road bike its a good option.
Past experience with A10s and different cams, with a chair on the side the less hot cam was a lot easier to ride .
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|by pushrod tom|
This sounds like a great project and has created much interest judging from the number of posts! A couple of comments. Supposing that your motor works out well, you will probably need a different clutch. As Allan mentioned the BNR is a very good and trouble free unit and you can use the standard charging system with it. At the least the transmission will have to be in perfect shape in order to stay in gear with the torque of the big motor. The 22 is big. I just put it in before assembling the cases. Then you can adjust at the rear as needed. The head steady is a vital part of the package. I have seen and experienced the damage from no or misapplied steady. Maybe someone here has done some work adapting an earlier style steady to the late frame. Save your money on the cam. If your stock 473 is in good shape it will work fine. Get some good, non racing, springs from Ed V.. Have fun, PRT
PS We have relatives in Austin. Whenever we can get down there maybe visit?
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