Roger King

Your original pistons are ordinary 1300ccm Crossflow pistons, but at +.090" oversize which is the largest overbore size available in standard spec, and gives a capacity of approx 1690ccm. The forgings are 83.5mm (this is the most common size, but others are available) and give a capacity of 1699ccm. Only a small difference, but you will need a rebore. It is essential that you have your machine shop leave the new bores with a plateau honed finished. If they can't do it, go elsewhere because the rings on the forged pistons demand it - with good reason because these rings are far more sophisticated than those of the standard pistons which basically date back to the 1960s. You will probably be OK with the diameter of the valve cut outs that come with the pistons, but you must check in case anything has been changed in the past. Bowl machining I can't advise on because I don't know what compression ratio you are aiming at. If you can tell me that, I can give you an approximation of the machining you need, but every engine I ever built had the pistons machined on an individual basis due to quite large variations in block height in production.

The usual reason that a Crossflow gets a bit smokey at around 25,000 miles is that the piston rings give up. It's not their fault, they were designed for 55bhp and are having to cope with around 120bhp at much higher revs. Forged pistons have much better rings (I'm talking about Accralites here) that seal much better, for longer, and as a bonus run with much lower friction.

It depends on the compression ratio you are aiming for, the height of your block, your valve sizes, etc. In general, for road use you will probably want to lower the compression ratio to suit your fuel octane and intended use; You need to do the measurements first but this is usually just a case of machining the bowl a little deeper. Valve size is down to the spec of your engine; you can get a good idea on this by removing the head of an old valve, turning the stem to a point and then using it down the valve guides as a punch to very lightly mark the piston crown. That will give you the valve centre within the piston cut-out which will allow you to work out if the pocket is large enough diameter. You need to allow a little more clearance for the fact that the piston will rock a little when running, particularly when cold. It is 17 years since I last built a Crossflow so I really can't be sure what diameter valve cut-outs the pistons come with these days; in my time, you could generally expect the cut-out diameter to be fine for standard size valves, but need enlarging for big valves.

Well, I confess that I haven't used any Accralites for some years, but unless they have changed the material (I believe they still use RR58) my figures still apply. And it won't rattle either although I have found some forged pistons from the USA rattle like a bag of spanners.

You should run .0045" to .005" clearance for normal use. I can't answer about the machining because it depends on your engine, but the things you need to look out for are that the valve pockets are of sufficient diameter for whatever valve size you are running and once that is sorted, what extra (if any) you need to take out of the bowl to give you the compression ratio you are wanting. This will vary according to block height, etc. It is rare to need to increase the depth of the valve pockets. I am assuming that you are running proper Crossflow pistons and not flat top pistons.

If you have an orange dizzy cap you probably have a Bosch dizzy, although be aware that I have seen a few aftermarket Lucas caps in orange. If you have the Bosch dizzy you are a lucky boy because the Lucas based "Caterham" distributor has a truly horrible advance curve that will lose you around 10bhp at full advance. It was introduced for unleaded fuel, was completely unnecessary, and seriously took the edge off performance. I think I read somewhere that your car is 1987? If so, the Bosch dizzy would have been standard, assuming the engine came from Caterham. Timing for the Bosch dizzy is 10 degrees BTDC at idle. Timing for the Lucas dizzy is 14 degrees BTDC at idle. You should then check max advance at around 4500rpm where the Bosch should show around 34 degrees BTDC. The Lucas will normally only get to around 24 degrees BTDC at the same revs, but it is EXTREMELY variable and could be anywhere between 19 degrees BTDC and 30 degrees BTDC. Even if you have the Bosch dizzy, you may well have the truly appalling Lucas electronic ignition system fitted. This can be easily identified by a rotor arm that has a slotted steel skirt attached to it (four slots). This skirt triggers the ignition, but often works loose on the rotor arm meaning that your ignition timing can go all over the place. If you have this, replace it at all costs with...................anything................ even contact breakers are an improvement. This system was introduced by Lucas as a cheap aftermarket electronic ignition system and was never intended for use in a high performance application - and even then it was marginal to say the least. Incidentally, don't confuse this system with the Lucas competition system which has a normal rotor arm. That system is reliable and very powerful.

It's impossible to be specific on this because the flange of the washers varies so much in depth. There is certainly no torque figure for this because you should be using a nyloc that is not fully tightened. What is certain is that you need some movement of the carbs on the manifold in order to prevent fuel frothing. A rough rule of thumb is to set up with about 10mm of up and down movement at the outer end of the ram pipes without forcing it. The best gasket to use between carbs and manifold is a Misab - you need one per barrel. This is different to what is seen in your illustration, being one large cross section 'O' ring bonded to an aluminium carrier that slots over the studs on the inlet manifold. This is more flexible, longer lasting and better sealing that what is in your photo (what you see there is a metal plate with a thin 'O' ring on each side). If you initially start with things fairly loose you can easily tighten the nuts up a bit if there is an air leak around the gasket (spray WD40 or similar over the joint to see if it is sucked in), but if you overtighten, aside from poor running, you run the risk of permanently deforming the 'O' rings so that they will never seal. Oh, and if that cold start enrichment cable is connected to anything, it's much better to remove it and give three pumps of the throttle when starting from cold.

This is the same principle used in compound steam engines where remaining pressure in the exhaust from the first cylinder is used to drive another cylinder. In fundamental principle, it is similar to the Atkinson cycle engine used in the Toyota Prius, although that engine achieves the effect in a completely different way through trick valve timing which allows the engine to breathe as if it were a 1300ccm unit, but then expand the combustion stroke to the size of a 1500ccm unit. Note that I'm not sure of the exact capacities here so the figures quoted are nominal.

The BDA is a leaker if not assembled properly. I'll start at the top. The cam cover is best fitted with sealant, either Silicone RTV or anaerobic type, and no gasket. The engine was designed in the era of cork/foil/cork gaskets which are utterly useless compared to modern gaskets and sealants. The only thing to add is that you shouldn't do this until you are happy with the way the engine is running, because the sealant is a nightmare to remove if you need access. It is possible that better solutions are available from companies like Cometic now. The rear camshaft plugs sometimes leak. They are simply an "O" ring seal and a thin smear of RTV around the ring will fix this (no jokes please). The biggest top end leak is usually from the front camshaft seals. These are perfectly fine seals, but there is no drain hole behind them to allow oil to run down to the cylinder head. The result of this is that you are left with the area directly behind the seal permanently full of oil which means that instead of holding back a few drips of oil, the seal has to cope with an ocean of oil - with inevitable results. This is easily dealt with if the engine is disassembled by drilling a small hole directly behind the seal which then allows oil to run down into the cylinder head. This needs to be done with great care with respect to positioning if you are not to cause further problems, but it is normally a 100% cure. It beats me why this was not done in production. The hoses are horrible and the only solution I have found is to replace them with softer, more heat resistant material. I haven't built any engines for 15 years now, but I would suggest a silicone hose might fit the bill. One hose is a breather, the other is an oil drain tube. Sump wise, you have the same problem with cork/foil/cork gaskets. Burtons used to produce solid cork gaskets that were much stronger and may still be available. It may be that Cometic or others now suppy something better. However, if you are stuck with the original gasket type, fit with Silicone RTV, but only tighten down very gently Leave for at least 8 hours to set and then fully tighten. This helps to stop the gasket squishing out of position as it is tightened.

Here's a straightforward explanation. There are two possible problems with unleaded fuel - valve seat wear and potential damage from detonation. The latter is solely an issue with the octane rating of the fuel because initially, unleaded was only available at an octane rating of 95ron compared to the 4* rating of around 98ron. This lower octane could theoretically cause detonation and has nothing whatever to do with the fact that the fuel happens to be unleaded. In any case, superunleaded has now been available for decades if this is an issue for your engine. The "unleaded" Caterham engine modifications consisted solely of a distributor change, which drastically reduced the ignition timing at full advance; this was done to prevent the above mentioned detonation, but reduced performance because the engine was running sub-optimally Merely changing to a distributor with a normal advance curve is worth around 10bhp and experience has now shown that this is usually absolutely fine on standard unleaded fuel with an unmodified engine. I think there was originally a sort of paranoia about detonation due to the drop in octane rating between 4* fuel and standard unleaded and, perhaps, enough testing wasn't carried out. You can always run on superunleaded if you want to be bulletproof. The real issue with unleaded is accelerated exhaust valve seat wear on engines (such as the Crossflow) that do not have hardened exhaust valve seats. Caterham did nothing to address this, I suspect for two reasons. 1) The average Caterham does a much, much, lower mileage than most cars and damage would therefore not appear for some time. A cynic might say that this would push such problems out of the warranty period. 2) The Crossflow is actually fairly OK (not perfect) with unleaded fuel because it breathes reasonably well and therefore there is less build up of heat around the exhaust valve seats. By contrast, the A-series engine (Mini, Marina, etc) suffers from unleaded within a few hundred miles because it doesn't breathe so well and the exhaust valve seats get much hotter. As commented by several, they have been able to run with just an unleaded additive such as Millers VSP for fairly long periods without damage. However, the real solution is to fit hardened valve seats to the cylinder head which will provide a permanent answer with no additives required. It is also advisable to make sure that the exhaust valves themselves are suitable for unleaded (most will be these days).

Seconded Although I would amend "carnage" to read "catastrophic carnage".

Well thanks for the embarrassment of revealing to the world just how dreadful my handwriting is! If only I'd been a doctor.

The AX block will generally go to 85.9mm bore (1800ccm) but there is always a risk that you have a bad'un so it is safer (but not guaranteed) to stick with 85mm unless you are prepared to have your block checked for bore wall thickness. I'm not sure you can even get 85.9mm pistons these days. The 83.5mm pistons will give 1700ccm and this is approx .010" bigger bore than a standard Supersprint which means that even worn bores will probably be capable of being cleaned up if you rebore to that size. Whatever you do, please make sure that you use a properly equipped machine shop that can provide you with a plateau honed bore finish. Decades ago, when we went from conventional honed bores to plateau honed, we found that we had 100% eliminated the occasional cases of smoky engine that used to occur. BUT, there are still plenty of machine shops who don't use the plateaued finish.

Yes, yes, yes. I have only used Omega, Cosworth and Accralite, but they have several advantages. They don't break like the standard Supersprint 1300 pistons often do (they were after all, originally designed for around 50bhp at 5500rpm max); the rings seal much better and last far longer; they have much lower mass; they run with greatly reduced friction (to the extent that you can feel the difference when installing them by hand - this is largely down to the rings again); you can run higher compression ratios (depending on the engine spec) in safety. Overall, we used to find a gain of around 10bhp on a Supersprint if we did nothing except change the pistons, largely due to the lower friction and better sealing rings. The lower mass did no harm for throttle response either. There is, of course, a downside - cost.

Certainly, having the correct float levels is important, although a mil. out here and there will not be the end of the world. Have you checked the ignition timing? Ideally, you need around 12 degrees at idle and around 34 degrees at full advance, assuming you are running on 95ron fuel and have the standard Supersprint compression ratio. The above figures are only relevant if you are running 2D mapping. If you have 3D mapping, light throttle advance figures should be much greater.

7000rpm is a little fast for idle! I'd try and drop it by an order of magnitude or thereabouts. There is no right answer for tickover speed because it can depend so much on the engine spec, particularly the cam profile (which also has a significant effect on airflow at idle). I'd say that typically you'd see between 700rpm and 1100rpm (the latter for full race spec). There is no virtue in trying to go as low as possible; apart from possibly affecting low speed throttle response, a very low idle speed is not good for camshaft wear. Assuming you are jetted correctly for your engine spec, the two main factors affecting idle smoothness are carburettor balance and idle screw setting. Get the balance as near as you can and then wind all four idle mixture screws in until they seat - HUGE WARNING HERE, THERE IS ONLY A VERY SMALL INCREASE IN RESISTANCE WHEN THE IDLE SCREWS MAKE CONTACT WITH THE SEATS. IF YOU KEEP ON TURNING YOU WILL DAMAGE THE IDLE SCREW SEATS BEYOND REPAIR. Once this is done, open all of the idle screws 2.5 turns and then see how the engine runs. If it is poor unwind all screws another .25 of a turn (or you may need to wind them back in again .25 of a turn instead). Keep doing this until the engine runs as well as possible. Now check the balance again and adjust if necessary. Once this is done you need to adjust each idle mixture screw individually until you get the best idle. You many find that some need winding in a little and some need winding out. There are no hard and fast rules about how far out the idle mixture screws should be; it varies from engine to engine and from carburettor to carburettor - some engines might need them out by roughly .5 of turn and others might need roughly 3.5 turns out. I should add that if you have the standard 45F9 idle jets, there is usually a huge improvement in slow speed running if you change to 50F9 instead. You will need to adjust the idle mixture screws to suit the change.

Is this happening under all conditions, i.e. light throttle, full throttle, low revs, high revs? If it is under all conditions, it is more likely to be an ignition fault and conversely, if it only occurs under some conditions a carb fault is more likely. Assuming it is a carb problem, it seems unlikely that fuel is failing to get into the float chamber since number 2 is functioning. Firstly, use a torch and a mirror to look down the ram pipes as you pump the throttle wide open (engine off at this point). You should see fuel squirting out from the pump jets onto the throttle butterflies. If number 2 does and number 1 doesn't, you probably have a blockage in the jet or the feed to it so check everything carefully. If neither barrel works, the mechanism may have stuck; this can usually be freed by removing the top of the carburettor and waggling the pump rod. It is also possible that someone has failed to reinstall something, causing it to stop it working. If this is OK then it could be a jet blockage. Far and away the most likely is the idle jet which is tiny, so check it. I have rarely seen a main jet block because they're so big, but check anyway. I would also suggest taking all jets out and inspecting them to make sure that you have the same ones fitted to all barrels. Next, have you set up the idle mixture screws? If not, it is possible that the one for number 1 is screwed fully home and won't let any fuel through. This will affect the engine at idle and at light throttle. Paul W has suggested checking the lock screws underneath the carbs - good idea. These locate the choke and aux vents. If the aux vent one is missing (this is the one nearest to the ram pipe), the aux vent can rotate and block off the fuel supply from the main jet. If this has happened, the engine will probably run OK at idle and light throttle but misfire on large throttle openings. Finally, was the compression test carried out with wide open throttle? If not, the results will be meaningless and the test should be done again (don't forget to disconnect the ignition first), ideally with a warm engine.

If the engine is a Sprint, rather than a SuperSprint (the rocker covers are very confusingly worded), it will almost certainly be an A2 profile. I believe that later engines from the factory actually just used the standard Ford GT cam. The A2 is actually a Cosworth profile, but you can look up all the details on the Kent Cams website.

I've never seen a Crossflow suitable for unleaded without modification. Stem seals may indeed be a problem, but so might valve guide/valve wear. Most likely though, if you have standard Supersprint pistons, is that the rings have given up. They are seriously overstressed with this state of tune and generally last only around 15,000 to 20,000 miles. The best solution for this is forged pistons with a modern ring pack. Wear issues associated with unleaded are the valve seats (exhausts specifically), valve guides and valve stems. Many Caterhams were fitted with quite good quality valves which were unfortunately only marginally compatible with the standard cast iron guides. Best solution here is either to line the guides with a bronze faced liner, or fit separate, bronze guides.

If the plumbing is done sensibly, the elbow is under no great strain. In this situation, most cast rocker covers are chunky enough to tap for a 3/8" BSPT thread which is what a lot of the available elbows have. Do fit it with one of Loctite's hydraulic sealants though.

Degrease thoroughly and use one of Loctite's thread sealants.

That has some merit, but in one case at least, it won't work. The oil gallery that runs across the Crossflow block between cylinders 2 and 3 has a plug in one end, but the engine mounting fits over it when bolted in position. The Hex head would prevent the mounting from seating onto the block properly.

Great stuff. You'll probably find things get even better with balancing and setting up of the idle mixture screws.

It doesn't really matter where the pipe is introduced into the rocker cover so long as it isn't close to the rear breather outlet leading to the catch tank.

That is indeed for a wet sump engine. A dry sump engine has no need of the crankcase breather because the scavenge pump removes any excess pressure from the bottom of the engine.