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Is the 731 cam any good - sought after ?!

cheers

Andrew

This is an old Special Tuning cam it was a halfwayhouse between s cam and 649 race , there are much better profiles around nowadays but if it is a genuine 731 it will be pin drive and to use in 1275 block you will need the correct oil pump now rare if it was spider drive it was a 800 I did not like this cam as had lumpy tick over but not much top end ok in a 1098 sprite back in the day

I have used the ST 731 a number of times over the years. Stock class autocrossing/sprinting to you I think. Late 60s early 70s Cooper S 1275 bored 1293, 10 to 1 CR, ST 731, big valve head. Twin 1 1/4 SUs. No lumpy idle ran fine no worse. Cam is better than most will say. Looking for big improvement you will be let down, no worse maybe a little better sure. I believe I have one in a engine I'd like to sell. 1275 GT block, EN 40 B crank, S rods, 6cc dish 1293, 940 head big intake std exhaust, forged S rockets, ST 731 cam, duplex gears and chain, new two part S balancer and pre verto flywheel, blue spring up rated disc. Fresh build, balanced, decked, run in on test stand 20 min. Attached to 1128 remote S ratios HS outputs, A+ diff cage 3.44. It runs very nice at idle and has no issues running on twin 1 1/4 s or a single 1 3/4. There was one in my stock class car, one in my lawyers car ( which he still drives 40 years later ) and this engine I built recently. That was the last NOS one I had on hand. I have the empty tubes don't think I'd pay dear for another. Steve (CTR)

Just in case I think $6000. would be in line for this unit. It could be stripped to confirm build.

I run a 731 in one of my cars its be a good all round cam dated but good no doubt new rally spec cams are a much better option, I also run a 544 in another car again probably much better newer cams for that application but I wanted to use period cams and tuning parts were possible
cheers MZ

The 731 has decent timing for a fast road cam, but lift is no more than a standard road cam. Probably would work much better in a 1275 with 1.5 lift rockers, and possibly also advancing the cam by a few degrees.

The AC Dodds's RS+ cam profiles looks much like 731 similarly advanced with extra lift. But RS+ lobe shapes and opening profiles may well be more radical than the BMC grind.

They fitted these Cams to our locally put together Highway Patrol Cooper Ss and Clubman GTs. They also ran a head that was produced by Lynx Engineering and were built to meet the local Police Highway Patrol requirements, which included 'a 100 MPH Pursuit capability' which on test isn't it's peak speed, but average speed

They were in the day a good cam on the small bore engines but like anything, only when set up right. i tried one long ago and thought it an improvement for sure, but nothing to write home about in a 1275, though in an 1100 I felt it gave a higher percentage gain.

Spider wrote:They fitted these Cams to our locally put together Highway Patrol Cooper Ss and Clubman GTs. They also ran a head that was produced by Lynx Engineering and were built to meet the local Police Highway Patrol requirements, which included 'a 100 MPH Pursuit capability' which on test isn't it's peak speed, but average speed

Hello Spider,
I have one of those ex police MkII very early in the SPO41 batch. Have owned it since the mid 70s and the cam in it when I rebuilt it was a 997 cooper cam with 3/8 inch lobes. The cam might have been installed earlier by the first non-police owner, but it idled happily and pulled well right through the rev range and really took off at 3,500 rpm and kept going into the 80 mph zone (when I slowed down).
Could the 997 cam have been original police spec?
What might be a "similar" cam today?

Aussie Bill B wrote:

Spider wrote:They fitted these Cams to our locally put together Highway Patrol Cooper Ss and Clubman GTs. They also ran a head that was produced by Lynx Engineering and were built to meet the local Police Highway Patrol requirements, which included 'a 100 MPH Pursuit capability' which on test isn't it's peak speed, but average speed

Hello Spider,
I have one of those ex police MkII very early in the SPO41 batch. Have owned it since the mid 70s and the cam in it when I rebuilt it was a 997 cooper cam with 3/8 inch lobes. The cam might have been installed earlier by the first non-police owner, but it idled happily and pulled well right through the rev range and really took off at 3,500 rpm and kept going into the 80 mph zone (when I slowed down).
Could the 997 cam have been original police spec?
What might be a "similar" cam today?

Hey Bill, they may have run a different cam in the earlier HP Cars to the later ones though the MKII SPO41 does refer to the later builds, I don't have a copy of the MKII SPO 41, however The Mini Clubman Series SPO 28 lists an AEA800 which is actually the Spider drive version of the AEA731. My (late) Brother's Clubman GT is ex-Highway Patrol. I was pretty sure the SPO 28 engine spec was a copy of that from SPO 41.

Nice car you have there! Quite rare, especially these days. Many many years ago I bought one of the last Round Nose HP car, the model that had the flappy door handles, it was fairly rusty and at that time, considered well beyond economic repair, so I stripped it out took what I wanted, sold off the rest, but no one would touch the body so that went off to the scrappers. When I think back now, it definitely would be worth repairing in more recent times. Ha, nothing's forever as they say.

I always thought 731s came on song too far up the rev range....

Interesting letter re 731 cam from Downton.

Thanks Mark an interesting letter

Interesting letter Mark!

Thanks for posting.

Aussie Bill B wrote:

Spider wrote:They fitted these Cams to our locally put together Highway Patrol Cooper Ss and Clubman GTs. They also ran a head that was produced by Lynx Engineering and were built to meet the local Police Highway Patrol requirements, which included 'a 100 MPH Pursuit capability' which on test isn't it's peak speed, but average speed

Could the 997 cam have been original police spec?

All the documentation I have seen from BMC Australia on the pursuit Cooper S supplied to NSW Police shows that the Mark 1 and all Mark 2 Cooper S's up to car #2371 were stock standard from a performance perspective. The only difference between them and cars sold to the public was lowered front seats (SPO16), racing disk brake pads (SPO26) and reversing lights (SPO25). From car #2372 Special Production Order 41 was adopted, and this became SPO28 when applied to the Clubman GT, but the basic mechanical specification was the same. The only camshaft profile documented is 731 and later 800, as Spider said. I'm about to strip my unmolested SPO41 engine which should confirm the theory translated into practice.

I have a similar letter from Goodall re. the 731. It was a couple of years later, as I recall. It said that they didn't recommend the 731 for any application.

I have been having a bit of a dig around the 731 cam and applications and it was sold by ST as a half race cam but as others have said rightly its not a good choice in a 1275 engine at all but will give fair results on 1100cc motors and better on 850 and 1000 but ONLY with the right specification engine mods ,as one well known engine builder say "install a 731 cam,lose all the bottom end power and gain almost nothing at the top " .Well mines been in for 17 years and it could well stay for another 17 years ,if it aint broke I wont fix it