Race cams and carbs

[John Bunting]

Hi there,
Has anybody used the 2+2 cam and would like to tell me how it is on the road, I don't mind lossing a little torque Morini's have plenty. also anybody used Keihin flatslide or Mikuni pump jet carbs and would like to share there experiance.
Looking forward to hearing from you
John

[morini_tom]

Hi John,

I have a 2+2 in my 501 engined dart. I've not had an L5 in it to compare back to back the relative merits, but I wouldn't change my current setup without a lot of persuasion. I've heard people say the 2+2 is all top end and I've also heard people say it's a lumpy 'sidecar' cam, so not sure anyone really knows! From my experiance the dart pulls cleanly from a couple of thousand right up to about 9000, although it's not pulling as hard from about 8200. I'd like to try a different ignition system on it and keep the spark advance right the way up if possible, but that's time and money I don't have for it right now. It's happy pottering around town off tickover and it does idle, although you can tell that these regions aren't where the motor's working best. On track I wouldn't really want any more power, the dart's chassis is at its limit in the curent state of tune, despite a cagiva mito front end. Bigger rear tyre and stiffer swingarm needed if I want to go further, but it is primarily a roadbike so there's not much need to.

I had it dyno'd just after I built it 5 years back with the previous 2+2 cam'd 501 motor. At the time I had PHBH30 carbs mated to the standard dart airbox which were only roughly jetted and it didn't run nicely- used to bog down all the time. Other than the carbs, cam and roller bearing conversion the 501 was standard. The exhaust system was a badly made 2 into 1 which got the gases out of the engine but not much more- the front primary was about twice as long as the rear, and (As I embarrasingly found out after knackering many chains) the front sprocket was a 530, mated to a 520 o ring chain... Despite all this I got about 40BHP at the back wheel, at something like 7500rpm and 40Nm from 4000 all the way up to 6500, although there was a big hole around 5500.

I'd like to get it back on the dyno now I've developed it properly, but just from riding it I can tell it's orders of magnitude better. The current spec is:

501 motor, roller main bearing conversion, lightened and balanced crank and rods, 2+2 cam, machined cases for cam removal through primary drive side bearing, PHBH30 carbs, de-restricted airbox with ITG filter, thin head and base gaskets, mikuni vacuum fuel pump and a 2 into 1 into 2 exhaust system made by Alex at NLM inspired by the valentini systems.

[John Bunting]

Thanks for the info Thom, would it be possible for me to have a look at your bike when next in the UK? I base myself in Wellingborough, just around the corner and should be back for 3 weeks in April/May.
I have lightened all the internals of my 81 Strada, put a pollishing mop down the ports, but not removed metal on the advice of NLM, increased the valve lift 1mm by using offset rockers and fitted NLM ignition pickups, externally the bike looks standard apart from fitting rearsets.
I had bought a KentCams reground L5 cam from NLM but on checking found it had the same lift as my standard 500 came so opted for offset rockers.
Look forward to hearing from you
John

[morini_tom]

John,

no problem, just let me know when you're in the area.

Regarding my 2+2 cam, I had it profiled onto a strada cam. To maintain the lift I think they took the base circle down. I really should have noted the measurements when I built the engine.

Being a late 501 motor I have the flywheel mounted pickups and standard dart cdi box. For now it's fine but eventually I'd like to map the ignition myself.

Sounds like your strada should be pretty quick though...

[EVguru]

I had bought a KentCams reground L5 cam from NLM but on checking found it had the same lift as my standard 500 came so opted for offset rockers.

The amount of flow may not increase very much above standard lift without more extensive porting. This mistake has been made many many times over the years, even by factory race teams. Flow bench testing has pretty much eliminated it in professional circles. Increasing the rocker ratio can put a lot of stress on the cam, lifters, pushrods, etc. I hope you checked for coil bind! Converting the rockers to needle rollers may actually get you more actual valve lift due to reduced friction and flex! The L5 has much longer duration than the 500 cam (which is sort of a high lift 350 Strada profile).

Everything has to work in concert and a dynamometer is really the only way to tell if it is.

[John Bunting]

Hi EV,
So far my 1mm offset rockers are working fine, I had used much bigger offset in race Mini engines before, and checked everything before the mods for coil binding, even with the offsets there is still plenty of allowance for more lift, no chance of finding a Dyno here in Nigeria, I would think the nearest is at least 4000Km away, a blast up the road is the best I can do.
I knew the L5 cam had more duration but suspected the softer 500 cam with a little more lift would be effective, but have no way to compare, as you say lots of heads, a flow bench and Dyno time would be the way to go, but here in the sticks my Strada is something for me to play with at weekends.
I'm trying to pick the brains of you lot out there for any further developements I can do.
Keep the info coming
Thanks
John

[EVguru]

I'd slightly missread your message I think. I now take it to mean you're using offset rockers with the 500 cam, not the L5.

The 'A' series engine is a special case. Sir Alec Issigonis thought it too antiquated to use in the Morris Minor! The reason for the high ratio rockers is the limited lifter diameter. You simply can't use too high a lift cam or you run off the edge of the lifter.

Morini seem to have been very conservative with the 500 engine compared with the 350. If the 500 was in the same state of tune as even a 350 Strada, then it would be putting out 50bhp rather than 42bhp. My personal theory is that they might have been worried about the longevity of the plain timing side bearing. When this is conerted back to a rolling element bearing like the early 350 engines (but with a roller rather than a deep groove ball) the 500 can be taken to 11,000rpm acording to NLM.

If you decide you'd like to try a 2+2 (which still doesn't have more lift, but is even longer duration) then let me know as I may be having a couple ground soon. I'd even take your L5 in part-ex.

[huub]

501 motor, roller main bearing conversion, lightened and balanced crank and rods, 2+2 cam, machined cases for cam removal through primary drive side bearing,

machined cases to ease cam removal? now that is something i have been planning for years.
anybody has pictures of the modified cases?

[mgill]

I don't mean to hijack the thread, but, could someone explain "off-set rockers"?

[morini_tom]

Huub,

annoyingly I didn't take pictures and it's hidden behind the primary drive case now! It was pretty easy, I bored the primary drive side all the way through so the cam and bearing can pass through. I then machined a circlip groove on the outside to retain the bearing. Camshaft removal is not a 10 minute job but a damn sight easier than splitting the cases: clutch and primary drive cover off, pushrods out, camshaft pulley off. You can use a strong magnet on a stick to hold the followers in or a dummy cam which you use to push the cam out with and which stops the followers dropping out (if that happens it's engine apart time!!)

[John Bunting]

Hi mgill,
As I started this I had better answer.
By moving the pivot point of the rocker arm closer to the tappit adjuster screw you alter the rocker arm ratio and increase the lift on the valve, Morini's have quite small valves, restrictive port design and not too much valve lift, the more it can breath the better it will go if it all hangs together. Oh and the good thing about offset rockers, they are cheap and you don't have to split or modify the cases to change cams.
I only offset my rockers 1mm by making eccentric bushes, with race Mini engines I have used purpose made much bigger offset rockers having needle bearings on the rocker shaft and valve pad in conjunction with high lift race cams to very good effect.
Hope that clears things for you?
Regards
John

[mgill]

I only offset my rockers 1mm by making eccentric bushes, with race Mini engines I have used purpose made much bigger offset rockers having needle bearings on the rocker shaft and valve pad in conjunction with high lift race cams to very good effect.
Hope that clears things for you?

Thanks for explaining that. So by moving the fulcrum 1mm closer to the adjuster tappet you would increase lift by
1.375mm, the original ratio being 1:1.375, is that correct?

[huub]

annoyingly I didn't take pictures and it's hidden behind the primary drive case now! It was pretty easy, I bored the primary drive side all the way through so the cam and bearing can pass through. I then machined a circlip groove on the outside to retain the bearing. Camshaft removal is not a 10 minute job but a damn sight easier than splitting the cases: clutch and primary drive cover off, pushrods out, camshaft pulley off. You can use a strong magnet on a stick to hold the followers in or a dummy cam which you use to push the cam out with and which stops the followers dropping out (if that happens it's engine apart time!!)[quote][/quote]

now that is a lot easier than i was thinking , i was thinking of a bearing housing , like a guzzi main bearing.
if the hole from the original can bearing is big enough that simplifies life.
i have gott a spare set of cases lying around , i see a night behind the milling machine coming.

cheers,
Hubert

[John Bunting]

Hi mgill,
I seem to remember (Alzhiemers again) the std ratio as being 1.4 to 1 and with the offset it was 1.5 to 1, which lifted the valve using the std 500 cam a gnats cock higher than the L5 cam if used with std rockers. So a cheap mod if you have workshop facilities, no extra strain on valve gear over the L5 cam, easy and quick to install, maybe a little more tappit noise as you must run a little more tappit clearance.
I have just bought a 2+2 cam from Italy, so If any body has a 501 engine for sale I would like to hear from you.
Regards
John