Nick Jones
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Everything posted by Nick Jones
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2.5 grunt plus low first gear does break 3.27 diffs...... plenty have proven this........ just a matter of time Tim...... (having watched an appreciated your Prescott video :)) Nick
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You should check the ring gaps on all compression rings by pushing them down the bore about half way with a ringless piston and then measuring the gap with feeler gauges. There will probably be a bit of paper with your pistons telling you what the gap should be. The one from my County brand ones says 0.003 - 0.004" per inch of piston diameter...... so 0.009 - 0.012" gap. Too small is the bigger risk as if the gaps close right up when the engine is hot the rings will break. If you get a huge gap it suggests the rings are the wrong size for the bore (std rings in +0.020 bore say) Did you ever determine what caused the original failure? Any pics of the wreckage? Cheers Nick
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99176 wrote:Much better to measure piston heights using micrometer depth gauge at centre of piston. Deck heights are a subject in themselves. I'll come clean what I run when everyone else 'fesses up'. I'm sure this is true but I don't have one. I'm getting more consistent results now I'm turning the engine over a couple of times before measuring and measuring in the centre of the piston. Measuring all pots with the same rod/piston combo (with dti in centre of piston)shows that the crank throws are equal within 0.05mm (0.002"). Hopefully will get the best combination sorted over the weekend. Looks like eventual deck height will be around 0.005". I like squish - not that there's squish area worth a damn on the 2.5 head - 2.0 L much better! Nick
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Hardened seats needed for exhaust valves only. Inlet seats just need re-cutting as lightly as possible to clean them up. Exhaust valves might need upgrading for unleaded but probably ok as are. Standard guides are fine. Nick
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If you are planning a full rebuild of the 2.5 it doesn't matter all that much which engine you start with as the major bits are the same on all. Therefore no reason to pay over the odds just because it's claimed to be ex-TR6 or whatever. My recipe, based on a 2.5 PI MG prefix engine Rebore +0.020" and new pistons (because it needed it) Crank ground 0.010" (because it needed it) Crank and flywheel balanced (Vitesse flywheel) Rods and pistons all weight matched to 0.5g Assembled with attention to even deck heights, 308778 PI 132bhp cam (good used) with new followers Toleranced oil pump Head (based on original PI head) Home porting job as per http://sideways-technologies.co.uk/forums/index.php/topic/6080-nicks-diy-head/ New manganese bronze guides and SS valves with unleaded inserts on the exhausts. Skimmed for 10.5:1 CR (will be mostly running on lpg - advise less for petrol! - though this will depend on cam choice) EFI and 3D distributorless ignition controlled by Megasquirt MS2 (already in the car and running the old engine, a smokey, rattly old ruin) TR6 twin-downpipe exhaust manifold Hoping for a torquey, docile and economical 140 - 145 bhp. Assembling bottom end at present. Nick
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Certainly should have springs. The carbs cannot correctly meter the mixture without them - will tend to make the engine run leaner as the piston can rise higher at a given flow rate reducing the vacuum over the jets. Size needed depends on whether you have the ball bearing dashpots (late cars only) which uses the big springs of the plain bush daspots which uses the smaller springs. There are also (at least) 2 different spring weights (red or yellow) - you need to get the right ones. You should probably check to see what needles are fitted. Cheers Nick
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Chris's progressive springs are good. They do ideally need a bit more damping than the standard dampers give IMO. Nick
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I've had a couple of those - I think it's a factory spare. Nick
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I'm inclined to agree with Bill. Having done a certain amount of digging around in various 6 cylinder water jackets recently I can certainly vouch for the large amounts of muck that lurk in there. You might find that the black muck is slightly magnetic (Fe3O4 is magnetite) - which would prove it's just ancient deposits disturbed in the water jacket. I did find some magnetic black powder in one of the blocks I've been working on - which was also from a car that had been stood a long time. Probably worth flushing the cooling system again before doing anything drastic. Nick
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Richard_B wrote:When in doubt, whip it out ::) I agree.... it is so damn heavy though. They seem to be breeding in my garage and they stay right where they are if you bump into them...... Nick
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Possible, but not a lot of fun or perhaps the way to get the best result. You'll need to raise the engine quite a bit and/or remove the rack to gain access to the front end. You may need to dunk the piston in hot water before you can push the gudgeon pin out (even after removing the circlips!). One other thing that would bother me is you will need to hone that cylinder before refitting piston (good used?) and new rings and just how you'll get the honing dust out of the engine..... Also - how has the piston damage occurred? Standard engine? Was it pinking horribly? Matching valve damage? Nick
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While you have the sump off you should take a look at the bearings. They can have a greater effect on oil pressure than knackered oil pump. It is possible to change all the shells and thrust washers with the engine in, though it is a pain to do the front main. I'd suggest dropping the centre main cap for sure - it will almost certainly be tired - it's always the most worn as it takes the most thump. If the rear main is only a bit worn I'd be tempted to leave the front one alone as you have to remove the alloy bridge piece to get at it and this usually busts the front plate gasket (even if you are really careful) making it hard to get a decent seal on reassembly. Big ends usually need doing..... as do the thrusts. Be very careful to put the thrusts in the right way round! Nick
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Alec, Where did the 0.065" come from? I gave 0.0065" (false precision!) as the lowest deck height with highest being near-flush. Rods are the originals. I'll have a go at evening things up a little more by swapping parts around. Piston measurements were a quick and dirty vernier between the top of the pin bore and the crown, just for comparison purposes. There are variations, but they are very small. Measured the recesses in my other block today and they are even less at 0.30 - 0.32mm. That's not been messed with since it last ran though it is a factory rebuild so may have been decked before. Having looked at and measured the new gasket I think it'll be fine. Once I've figured the best piston/rod/bore combinations for most even deck height I'll build it up. Nick
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In what respect is your old pump out of tolerance? If it's end float there are ways of dealing with that involving a sheet of glass, some fine wet/dry paper and elbow grease...... Do you have an oil pressure gauge? If it can manage more than 10 - 15 psi at hot (properly hot) idle then there's not alot wrong with pump or bearings. There isn't meant to be loads of oil to the top end. It's actually metered by a flat on the rear cam journal. Might be worth checking the oil-way that goes down from the block face to said journal is clear (it's a straight drilling) but I expect it is. Problem with the metered flow is that when the rocker shaft and/or rockers wear the oil all escapes through the excessive gaps nearest to the supply point and the furthest ones get starved. The external feed kit will happily mask this problem but you will be dumping a fair bit of oil up top through the enlarged gaps leading to oil burning and possibly robbing oil from below. Correct cure is good shaft and rockers. I notice your tappet adjusters are wound all the way up...... suggests heavily skimmed head or wrong pushrods? Nick
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Thanks Andy - nice link that. Will have a better look later. Nick
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piman wrote:Hello Nick, ideally you want to match the piston heights, to even out the compression. Alec Yes, this is the plan - to try mix and match and find the most even combination. Pistons all measure the same so it's all in the rods and crank throws.
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Got my block back from the machinist. Has had "a very light tickle across the top to true it up" - which could be true as the engine number is still clearly visible. However, block recesses now measure at 0.35mm (0.014") which doesn't seem like much...... I've seen figures of anything between 0.025" and 0.038" being quoted as the correct, or at least acceptable depth. Anyone know what the book figure is and what the minimum you can get away with is? On a related subject, deck height is less than expected. This is slightly complicated by the pistons not being level in the bores (another story!) but two are more or less flush and the lowest is 0.0065" down. I always understood that they are about 0.025" down from the factory. This all seems to point to it having had at least 0.020" off but I'd not expect to see the engine no anymore (or only the ghost of it)? Cheers Nick
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It is basically straight-forward. Does not involve any serious messing with the diff. However...... in order to change the seals you have to pull the bearings off first. They are on there pretty tight and there is a high risk of damaging the bearings in the process (if not outright destroying them) as you can only pull on the outer race. You'll need some sort of bearing puller or suitable support plates for your press. Suggest having new bearings handy. Nick
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PRI - just avoid I think.... The thought of trying to set-up and balance 6 Kiehins...... eeew! :o As for the "independent rear suspension" '72 GT6 should have a rotoflex rear or a swing spring and what is offered there is not an upgrade for either of those, if it's an upgrade for anything. Have a good poke around on here and on the Sideways forum before parting with any cash! Nick
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Nylon fuel line acting as an (small) accumulator? Bosch pumps have a non-return valve, Lucas not. Nick
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Hi Christian, I prefer the earlier Strombergs - simpler, easier to adjust. Float height is important and so is fuel pressure. Some of the newer replacement fuel pumps produce too much pressure and force the needle valve open. This usually causes the carbs to leak fuel from the float chamber overflow channels into the air filters. The jets can wear oval especially if they've not been properly centred at some time. Have you checked that the needles are the correct one for the car? "Correct" might be a bit tricky if it has been modified though Cheers Nick
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Where is the gauge connected? The fuel pressure should remain constant. The more common fault is for the pressure to fall when the engine is working hard as more fuel is actually being used and the pump cannot keep up. Might be worth checking whether the fuel return pipe from the MU is clear as if there is no way for excess fuel to get back to the tank I guess this will cause the pressure to rise and also cause rich running. NIck
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You have a gauge don't you? Is the PRV causing the pressure to go high or low? It's a pretty simple device so if you are having problems with more than one of them I'd be wondering what else it could be or what could be causing the PRVs to misbehave? I know that when I added modern (ethanol containing) petrol to my PI it had a disturbing effect on the fossilised hydrocarbons in the system and led to all kinds of issues. Cleaned tank (horrible job) replaced all lines (likewise) and converted to EFI (bit extreme!). Works now, but the engine is knackered...... Cheers Nick
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Oil seals are specified by inside diameter (Shaft size) x outside diameter (housing bore) x thickness (less critical, typically 6 - 8mm) So by measuring the diameter of the crankshaft nose were the seal runs and the diameter of the housing you should get a pretty good idea. Of course, the numbers you get may not be a standard general engineering size quite a lot of the automotive ones are not. If you get the choice, a double lip seal usually seals better and Viton will last better in the hot, hostile conditions of the engine. Hope this helps Nick
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Oh yes....... 🙂 Nick