Discussion
my car is currently off the road so i can build a new engine heres the spec
doubble sprung polished skimmed 12g295 head
731 mini sport road/rally cam
lightened ballanced flywheel and pressure plate
rebore +0.20 with new pistons/rings
1.5 ratio forged rockers
central oil pickup
duplex timming set
block skimmed to match up to head
1.75 inch tube manifold with a superflow exhaust
as for carb/s either standard carb on alloy inlet or i have a set of twin 1.25 of manifold in the shed but i think it will be standard cos of insurance not sure yet
all and any advice will be helpful
doubble sprung polished skimmed 12g295 head
731 mini sport road/rally cam
lightened ballanced flywheel and pressure plate
rebore +0.20 with new pistons/rings
1.5 ratio forged rockers
central oil pickup
duplex timming set
block skimmed to match up to head
1.75 inch tube manifold with a superflow exhaust
as for carb/s either standard carb on alloy inlet or i have a set of twin 1.25 of manifold in the shed but i think it will be standard cos of insurance not sure yet
all and any advice will be helpful
The only things I'd say are :
If you are building it from scratch and can find a 295 head which hasn't been skimmed already, then get some flat topped pistons and deck the block to get your compression rather than doing an 80thou skim on the head.
I'd probably pick a more modern cam than the 731, an SW5 would be good, or a Kent 266 or 274 ?? If money's tight then the MG Metro cam is another option. Oh and I'd not bother with the 1.5 ratio rockers either. Don't go overboard on the valve springs as high poundage springs will kill the cam in double quick time.
Carb wise a servisable 1 1/2" HS SU or better still an HIF38 from a late mini or metro 1000 on a decent alloy inlet will be fine. The twins are good from asthetics and perceptively in throttle response, but not if insurance is going to be problem.
The rest looks ok, are you rebuilding the gearbox and diff at the same time ?? I always fanced building a decent 'thou, maybe with the single point fuel injection, just to see what a "modernised" version of the old A-series could do against the more modern alternatives !!
Phil.
If you are building it from scratch and can find a 295 head which hasn't been skimmed already, then get some flat topped pistons and deck the block to get your compression rather than doing an 80thou skim on the head.
I'd probably pick a more modern cam than the 731, an SW5 would be good, or a Kent 266 or 274 ?? If money's tight then the MG Metro cam is another option. Oh and I'd not bother with the 1.5 ratio rockers either. Don't go overboard on the valve springs as high poundage springs will kill the cam in double quick time.
Carb wise a servisable 1 1/2" HS SU or better still an HIF38 from a late mini or metro 1000 on a decent alloy inlet will be fine. The twins are good from asthetics and perceptively in throttle response, but not if insurance is going to be problem.
The rest looks ok, are you rebuilding the gearbox and diff at the same time ?? I always fanced building a decent 'thou, maybe with the single point fuel injection, just to see what a "modernised" version of the old A-series could do against the more modern alternatives !!
Phil.
id agree with phil, sw5 (or the minispares evo), no 1.5's, they will be a pain to fit and not do much on your spec of engine.
id also just fit std new single valve springs, modern springs are so much better and certainly capable of substained 6500 rpm. the doubles will just wear the cam out and rob power.
what ever 295 you get check it for cracking and make sure the valves are ok. the std vavles are nla (you can get rimflows, but budget for over 100 a set) so a bare one will need valves making for it unless your lucky.
its a while since i owned a tuned thou, but the last one with a 295 was my bros' with std flat tops and a genuine downton 295 (which i stupidly sold in a moment of money weakness!) used to fly, in the end it proved too much for the std pistons and the rings broke, the crankcase pressure got so bad that the oil was advancing up the outside of the bonnet!
we ran ours on a hif38 - twins are a black art and take a bit of learning to set up (old ones always need a rebuild and that cost a lot to get them right)
strangley, ive always fancied building a spi 1071 - ive got a mapable ecu that allows the fuel, ignition and rev limit to ve altered to it would be a nice little beast!
id also just fit std new single valve springs, modern springs are so much better and certainly capable of substained 6500 rpm. the doubles will just wear the cam out and rob power.
what ever 295 you get check it for cracking and make sure the valves are ok. the std vavles are nla (you can get rimflows, but budget for over 100 a set) so a bare one will need valves making for it unless your lucky.
its a while since i owned a tuned thou, but the last one with a 295 was my bros' with std flat tops and a genuine downton 295 (which i stupidly sold in a moment of money weakness!) used to fly, in the end it proved too much for the std pistons and the rings broke, the crankcase pressure got so bad that the oil was advancing up the outside of the bonnet!
we ran ours on a hif38 - twins are a black art and take a bit of learning to set up (old ones always need a rebuild and that cost a lot to get them right)
strangley, ive always fancied building a spi 1071 - ive got a mapable ecu that allows the fuel, ignition and rev limit to ve altered to it would be a nice little beast!
the 295 head is a standard one with standard cooper double valve springs is currently fitted to my current enigie and is ok but needs seats cutting in properly and new guides putting in. i think just putting the single 1.5 su on sounds the way to go. as for cam can you get a sw5 that fits the peg drive oil pump cos i dont want to faf on making spacers etc to fit diffrent pumps as ive been hold i would have to. its you think it would be wise to dump the 1.5 rockers al give them a miss. ive been told that by lightening the flywheel it will reduce the amount of tourque the engine has. how much do you think is a resanable power output to aim for 60-70 bhp and a cr of about 9.7-1 ive currently worked out the current cr and it is 8.5-1 ive worked out if i have it skimed 20thou and flat top pistons in i will achive the 9.7-1
oh ye and am going to put new syncromesh in the gear box and new seals etc
oh ye and am going to put new syncromesh in the gear box and new seals etc
Edited by robminiman on Wednesday 10th December 19:55
It'll invariably need a new oil pump when you rebuild the motor. Get the slot drive and put a decent cam in it. Things have come a long way since the the days of 731 profile. SW5 or Kent 266 are both excellent recommendations and 1.5 rockers will just rob you off mid range grunt whilst extending top end rpm and output (no point in a road car - it'll do your head in trying to access it) - ditch 'em. To keep the torque up stick with the single 1.5inch SU also.
Ah, the '731'cam. Lose all the low-end torque and gain precious little at the top end!
Actually the original Cooper 'S' 510 cam is quite nice in a road-going 998.
For a hotter and 'camier' engine the 276 is OK but a bit too much 'top-end' for town driving. I would look at the 266 or the MG Metro cams which are, in fact, quite similat in spec.
You only need 1.5 rockers if you intend to use up to 7000 rpm as you won't get any real advantage below about 5000 and it'll be much 'lumpier' below 3000.
Have you considered boring it to +0.080" and use the Hastings flat-top pistons which Mini Spares now offer. That makes it 1062 cc. I did that to a 998 last year, with a 510 cam and a flowed 295 head with a c.r. of 10.2:1 and it goes really well.
Actually the original Cooper 'S' 510 cam is quite nice in a road-going 998.
For a hotter and 'camier' engine the 276 is OK but a bit too much 'top-end' for town driving. I would look at the 266 or the MG Metro cams which are, in fact, quite similat in spec.
You only need 1.5 rockers if you intend to use up to 7000 rpm as you won't get any real advantage below about 5000 and it'll be much 'lumpier' below 3000.
Have you considered boring it to +0.080" and use the Hastings flat-top pistons which Mini Spares now offer. That makes it 1062 cc. I did that to a 998 last year, with a 510 cam and a flowed 295 head with a c.r. of 10.2:1 and it goes really well.
If you are sprinting or climbing look at the class structure first. The only class a Mini will be even close to competitive in will be up to 1400cc modified production using a blown 1.0litre unit (as equivalency formula is x 1.4). There is a couple of ultra rapid turbo 1.0litres on the Midlands sprint scene.
robminiman said:
ive been told that by lightening the flywheel it will reduce the amount of tourque the engine has.
This is not true, in fact lightening the flywheel actually increases the the amount of torque available at the wheels during acceleration which the entire point of them. However, ultra-light flywheels do make the engine easier to stall and tend to reduce idle quality somewhat which can make driving in traffic a pain.I too have heard somebody protesting that torque is reduced by lightening flywheels, and agree that it is not true. I may be no scientist, but do know torque is not generated by the flywheel, but the engine. Therefore the comment is worng, but the point whoever may have been trying to make is that the flywheel carries momentum, and a significant amount of it, so can help maintain revs, and torque availablity as a result of revs.
A lighter flywheel will allow the engine to spin up quicker (and slows down quicker), and is very noticeable on a 'good' engine (not necessarily a silly one), this will reduce loss, and increase available power & torque.
The SW5 and 274 I thought were developed for the spi 1.3 cars? So would have thought the 266 may be more suitable for you? The 274 is quite a mild, fast road cam, from what I recall, and on a 1.3, 1.5:1 rockers would benefit, but can as was said bring in a slight lumpy feel at idle. It is true that these rockers load the cam, but if you use a billet (new) cam blank which all the guys will do for you for not as much as you may think, and use lifters with a drain hole, which will assist the lubrication, and 'full' roller rocker gear, you will be equipped with some longevity others wouldn't have.
Spring heights will be crucial, as the finisher for cams is actually likely to come from too much lift and binding springs. If you know this is sorted, and the geom, great.
Only my 2p - new to this site, and good to see the real Mini gets discussed!
A lighter flywheel will allow the engine to spin up quicker (and slows down quicker), and is very noticeable on a 'good' engine (not necessarily a silly one), this will reduce loss, and increase available power & torque.
The SW5 and 274 I thought were developed for the spi 1.3 cars? So would have thought the 266 may be more suitable for you? The 274 is quite a mild, fast road cam, from what I recall, and on a 1.3, 1.5:1 rockers would benefit, but can as was said bring in a slight lumpy feel at idle. It is true that these rockers load the cam, but if you use a billet (new) cam blank which all the guys will do for you for not as much as you may think, and use lifters with a drain hole, which will assist the lubrication, and 'full' roller rocker gear, you will be equipped with some longevity others wouldn't have.
Spring heights will be crucial, as the finisher for cams is actually likely to come from too much lift and binding springs. If you know this is sorted, and the geom, great.
Only my 2p - new to this site, and good to see the real Mini gets discussed!
CarsOrBikes said:
. It is true that these rockers load the cam, but if you use a billet (new) cam blank which all the guys will do for you for not as much as you may think, and use lifters with a drain hole, which will assist the lubrication, and 'full' roller rocker gear, you will be equipped with some longevity others wouldn't have.
Sorry chap but that is bobbins. CarsorBikes - Full roller rockers are not a recommendation for any road engine - the reduction in friction being only justifiable on a full race/rally motor and then regular inspection is part of the preventative maintanence schedule. Since when has a roller cage bearing been suitable for a reciporocating motion? What happens when the cage collapses as it isn't fit for intented purpose, when one of those little needles gets free...? They are not - Bushed with a roller tip is far more durable and relieves the side loads on the valve guide - I've had a set on a well thrashed 1275 do 80K +. The other +ve point is that they are a hundred quid cheaper.The problem here is that if the car is to be used for competition only sometimes, but be a road-going daily-driver for most of the time, the compromise will not suit either application.
For hill climbs and sprints you'll need a very low-ratio diff which will make road-driving unpleasant. I run a 3.9 final drive in my rally car and that is too low geared for regular road use. If going more than about 60 road miles I always use a trailer. However, for hill climbs, even a 3.9 with 10" wheels would be too high, even though that's only about 85 mph at 6000 in top. Cruising at 4000 on the road I am only doing about 57 mph. More than 4000 cruising is very noisy with the S/C gears and S/C drop gears which you need for any sort of proper competition. Yes, I do use ear plugs when driving it on the road, but not when rallying it as I need to hear the co-driver.
You must decide what the priorities are. Is acceleration the prime requirement (as it will be for hill-climbing or sprinting)? If it is, then forget it as a smooth road car. Is top speed or a high cruising speed the main aim? In which case forget about hill climbing or sprints - it will be too over-geared and the clutch will soon burn out if you try to compete.
If you want to go club road-rallying, that's still another compromise. You can use a higher diff, say a 3.44 or 3.76, have some sound-proofing and even use a standard gearbox so long as you keep the maximum power to a sensible level, say around 65 bhp at the flywheel (remembering it's a basic 998).
Before you can finally spec. the engine, you need to have in mind the overall objective you wish to reach, then reach the best compromise for this.
It ain't easy, is it?!
For hill climbs and sprints you'll need a very low-ratio diff which will make road-driving unpleasant. I run a 3.9 final drive in my rally car and that is too low geared for regular road use. If going more than about 60 road miles I always use a trailer. However, for hill climbs, even a 3.9 with 10" wheels would be too high, even though that's only about 85 mph at 6000 in top. Cruising at 4000 on the road I am only doing about 57 mph. More than 4000 cruising is very noisy with the S/C gears and S/C drop gears which you need for any sort of proper competition. Yes, I do use ear plugs when driving it on the road, but not when rallying it as I need to hear the co-driver.
You must decide what the priorities are. Is acceleration the prime requirement (as it will be for hill-climbing or sprinting)? If it is, then forget it as a smooth road car. Is top speed or a high cruising speed the main aim? In which case forget about hill climbing or sprints - it will be too over-geared and the clutch will soon burn out if you try to compete.
If you want to go club road-rallying, that's still another compromise. You can use a higher diff, say a 3.44 or 3.76, have some sound-proofing and even use a standard gearbox so long as you keep the maximum power to a sensible level, say around 65 bhp at the flywheel (remembering it's a basic 998).
Before you can finally spec. the engine, you need to have in mind the overall objective you wish to reach, then reach the best compromise for this.
It ain't easy, is it?!
Edited by Cooperman on Monday 15th December 16:35
FWDRacer said:
CarsOrBikes said:
. It is true that these rockers load the cam, but if you use a billet (new) cam blank which all the guys will do for you for not as much as you may think, and use lifters with a drain hole, which will assist the lubrication, and 'full' roller rocker gear, you will be equipped with some longevity others wouldn't have.
Sorry chap but that is bobbins. CarsorBikes - Full roller rockers are not a recommendation for any road engine - the reduction in friction being only justifiable on a full race/rally motor and then regular inspection is part of the preventative maintanence schedule. Since when has a roller cage bearing been suitable for a reciporocating motion? What happens when the cage collapses as it isn't fit for intented purpose, when one of those little needles gets free...? They are not - Bushed with a roller tip is far more durable and relieves the side loads on the valve guide - I've had a set on a well thrashed 1275 do 80K +. The other +ve point is that they are a hundred quid cheaper.another issue with full rollers is that the rollers in the bearings 'chatter' on the rocker shaft and start to wear through the case hardening becasue they are moving such a small amount - a good few of the hi-po boys are actually going back to bushed ones as they are proving to be more reliable - a bit of brass swarf is better that mashed up needle bearings and roackershaft spaull.
i think the biggest cause of cam wear and problems comes from people simply bolting a set of rockers onto a motor without checking the crush lengths, spring poundages, lift etc etc. i see a lot of photos of problems in this area (none of which i can show here i think) from engine issues that can be directly attributed to 'fitment error'
The old question, "How cheaply can you build me an engine?" comes to mind. Of course, the correct answer should be "I can't build an engine cheaply". The only way to build an engine is by carrying out as many 'trial (or dummy) builds' as necessary. If you put a different rocker shaft ratio on and/or change the valve springs, you MUST do a trial build with an old head gasket in order to measure the spring coil clearances at full lift. Then you must have a minimum of 0.030" between coils - well, that's what I work to anyway.
You want a cheap engine build, then expect problems later on.
You want a cheap engine build, then expect problems later on.
Glad someone agrees about the spring clearances, but re: the full roller rockers, the little caged bearings cant get free. If you disassemble some proprietry brand rockers of this type, they are well made, and will have longevity. The mention of reciprocating bearings doesn't mean these higher specification components can't perform, the caged bearing is used on front and rear wheel drive car hubs travelling up to 200 mph speeds, or on the cranks of two stroke engines revving to sky high rpm, albeit with regular attention required, gearbox bearings subjected to massive forces etc. But considering proportionate sizes, full rollers are more than capable, they will give a silent engine, lower running temperatures, more stable clearances, greater accuracy, lighter reciprocating masses, and if issues arise the clearances will increase gradually, and faults may be discovered, these will be very rare. As opposed to the age old complaints of rocker shaft wear, found on cars with standard lift in standard engines.
Cheap builds have now been mentioned, where does that fit with saving 150 quid and using bushed rockers? Bushed rockers will be fine, but we can all do a little something to our engines that improve them, in my case the 65,000 miles covered mostly with a particular set of full roller rockers fitted, has been faultless in this respect, bar the need to renew the adjuster posts as the threads can begin to crack with long term use and adjustment, not because of bearing wear, but in my case the constant change of engine specs for development at the time.
The mention of them was more associated with the positive rather than negative effects of 1.5:1 over 1.3:1 lift, where higher lift will be better accompanied by an easier movement, potentially prolonging cam life.
This fella is investing in this motor, there are some areas worth considering investing more in rather than less.
Many people messing with Minis or the engines go to the likes of 'this world' and 'that spares' fitting anything the text of the catalogue says gives 10ps or 20mph or is blue or red anodised.
When someone may be in fact considering the replies here, as potential help, they may want to learn, and take note of valve geometry, cam type, piston crown shape, saving the head by reducing skim, as well as the pros and cons of lightening flywheels, and valve train type.
All good points.
good point with the f/d, leverage helps a lot, and good match to the engine output. 3.9 must be hard to use on the road? ? Depends on gearing too doesn't it.
Cheap builds have now been mentioned, where does that fit with saving 150 quid and using bushed rockers? Bushed rockers will be fine, but we can all do a little something to our engines that improve them, in my case the 65,000 miles covered mostly with a particular set of full roller rockers fitted, has been faultless in this respect, bar the need to renew the adjuster posts as the threads can begin to crack with long term use and adjustment, not because of bearing wear, but in my case the constant change of engine specs for development at the time.
The mention of them was more associated with the positive rather than negative effects of 1.5:1 over 1.3:1 lift, where higher lift will be better accompanied by an easier movement, potentially prolonging cam life.
This fella is investing in this motor, there are some areas worth considering investing more in rather than less.
Many people messing with Minis or the engines go to the likes of 'this world' and 'that spares' fitting anything the text of the catalogue says gives 10ps or 20mph or is blue or red anodised.
When someone may be in fact considering the replies here, as potential help, they may want to learn, and take note of valve geometry, cam type, piston crown shape, saving the head by reducing skim, as well as the pros and cons of lightening flywheels, and valve train type.
All good points.
good point with the f/d, leverage helps a lot, and good match to the engine output. 3.9 must be hard to use on the road? ? Depends on gearing too doesn't it.
cos
i dont think the bearings themselves are the problem with the full roller types, the problem with them is that because the rocker is only moving through a small arc (rather than rotating fully like a wheel bearing) the same part of the shaft is in contact with the same bearing, after a while the shaft starts to mark up and break throught the case hardening. ive seen a few shafts that have got a very distinctive shape where the rockers have been rubbing.
of course, this isnt a problem on a race motor as stuff gets inspected every couple of hundred miles.
id never advise full rollers to be run on a road engine unless it was very bespoke.
i dont think the bearings themselves are the problem with the full roller types, the problem with them is that because the rocker is only moving through a small arc (rather than rotating fully like a wheel bearing) the same part of the shaft is in contact with the same bearing, after a while the shaft starts to mark up and break throught the case hardening. ive seen a few shafts that have got a very distinctive shape where the rockers have been rubbing.
of course, this isnt a problem on a race motor as stuff gets inspected every couple of hundred miles.
id never advise full rollers to be run on a road engine unless it was very bespoke.
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