viperbl Posted November 1, 2008 Share Posted November 1, 2008 Guys, I rebuilt a K series VVC engine a few months back, got it running and it was running well (appart from the VVC not actually working). Revving well to 7.5k albeit without VVC helping it. It then started to not want to rev past 6k, but fine and dandy below that so I assumed the VVC machanism had maybe changed position so no rpm above 6k? anyway, I made a boob and dropped into 3rd for a corner, would have taken rpm to 6.5k - 6.8k which would be fine normally, but i'd forgotten about the 6k thing, anyway, poof of smoke and oil over me. So, on openning it up I find the following ... Broken Piston Broken Piston Here is the head, this is the strange thing, they valves look ok?!?1 Head Quick pic of one of the other pistons, they are all ok ... OK Piston What do you think happened? can valves hit pistons but look perfectly ok?? or has the piston just given up the ghost????? Edited by - viperbl on 1 Nov 2008 22:54:37 Link to comment Share on other sites More sharing options...
Johnty Lyons Posted November 1, 2008 Share Posted November 1, 2008 Not piston /valve contact it's ring lands failure Did you gap the rings correctly when fitting ?? I've not seen this before But I'm sure Oily has he'll be along in a minute with all the correct info jj N.I. L7C AR 🙆🏻 Membership No.3927. 240BHP 1900cc K Series 40th Anniversary Link to comment Share on other sites More sharing options...
Englishmaninwales Posted November 1, 2008 Share Posted November 1, 2008 Revving well to 7.5k albeit without VVC helping it. The standard 1800 pistons will break if revved regularily above 7000k rpm. Either limit to 6900 or fit forged pistons. Malcolm Link to comment Share on other sites More sharing options...
Grubbster Posted November 1, 2008 Share Posted November 1, 2008 I'm probably sailing too close to the wind - I have my limiter set to 7400 on standard pistons so I need to do something about that. How easy or hard is it to change pistons? If it is a big dismantleing job then maybe I'd best arrange other upgrades at the same time . . . Link to comment Share on other sites More sharing options...
viperbl Posted November 1, 2008 Author Share Posted November 1, 2008 Cheers guys, I was in a way hoping that it was just a piston failure and not something i'd done as such when building ... the pistons were used pistons so gaps "should" have been fine. I guess it was just their time ... Link to comment Share on other sites More sharing options...
Myles Posted November 1, 2008 Share Posted November 1, 2008 Hmm - I'm sure Oily will pop-up too. IN the meantime, were the pistons and liners matched though? And were they correcly aligned to previous usage (assuming that they matched)? 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester Racing 7s Ecosse™ 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
Steve, Carol and little Cl Posted November 1, 2008 Share Posted November 1, 2008 It looks very much like detonation has caused the failure. It´s quite common not only for pistons to fail in the centre when the engine runs heavily in det, but also at the edge. Piston three, although intact, appears to already show signs of a pending failure - look at the pitting aroung the edge in the same area of the failure of the other two pistons. After destroying numerous engines myself , and seeing many more slaughtered in the name of engine development , I have to say that it really does look very familar. Link to comment Share on other sites More sharing options...
Myles Posted November 1, 2008 Share Posted November 1, 2008 It's jolly-clean on P3 on that side, it must be said... 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester Racing 7s Ecosse™ 🙆🏻 🙆🏻 🙆🏻 🙆🏻 🙆🏻 Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
viperbl Posted November 1, 2008 Author Share Posted November 1, 2008 (btw, image name misleading, it was piston 2 that was cracked and the good piston was piston 1, not that it matters much, but thought I would mention anyways) Right, the pistons and lines where all matched, they had not been taken out the liners, they were marked 1 to 4 and direction of travel shown, so all good there. Hmm, detonation, now I was running a very similar map to my suppersport one, I wonder if because the VVC was not advancing the cams that I was actually running too much ignition up the top of the rev range??? Link to comment Share on other sites More sharing options...
rj Posted November 2, 2008 Share Posted November 2, 2008 viperbl, I don't think it's worth using second hand pistons of unknown origin, but if you still fancy used parts I have a set of VVC pistons which will be yours for nowt. They're still on the rods, which are single tang and hence the only parts of the lot which have sort of value. Link to comment Share on other sites More sharing options...
viperbl Posted November 2, 2008 Author Share Posted November 2, 2008 I defiantly hear you about using 2nd hand parts, but they did come from a very reliable source. I really appreciate the offer of the pistons RJ, although I am unsure of were to go from here. I do have my supersport engine sitting there in full working order still, so I might throw that back in for now, but ultimatly I want to build an R500 spec K series or go 220bhp or so duratec (with scope for more later) ... Back to my spreadsheet for more number crunching I guess!! Link to comment Share on other sites More sharing options...
rj Posted November 2, 2008 Share Posted November 2, 2008 viperbl, I was more thinking of my own "spare" pistons as being doubtful! Link to comment Share on other sites More sharing options...
Roger King Posted November 2, 2008 Share Posted November 2, 2008 That is not a broken piston, it is detonation damage, which means that the source of the problem will be the mapping, dodgy fuel, a faulty injector, poor fuel delivery, or a faulty sensor somewhere in the management system (I might have left something out). You could fit the world's strongest pistons, but if the fundamental problem still persists you will suffer the same type of failure again. The 'good' piston is suspiciously clean in the same area. This is likely to indicate that you have had the same problem to a lesser degree here too, since detonation blasts the carbon deposits away. Even if pistons appear good, they must be changed after an incident like this because they will almost certainly have been weakened. You need to examine the head very carefully for flatness, any sign of detonation damage around the gasket fire ring line and also hardness. Edited by - Roger King on 2 Nov 2008 11:46:40 Edited by - Roger King on 2 Nov 2008 11:49:42 Link to comment Share on other sites More sharing options...
david nelson Posted November 2, 2008 Share Posted November 2, 2008 Roger Thanks for the explinations. Most educational. Link to comment Share on other sites More sharing options...
Steve, Carol and little Cl Posted November 3, 2008 Share Posted November 3, 2008 Yep, quite agree with Roger. One thing to bear in mind, however, is that replacing all the pistons with new ones won't make the problem go away. If you were running a different ignition map than the one intended for a specific engine, you always run the risk of this sort of thing happening. Engineers spend ages running power curves with different setups under different conditions to ensure that an engine doesn't destroy itself in the field. I know, because I spent 5 years sat on test cells doing exactly this sort of work. If you're going to repair the engine, then you need to look at the ignition map that your running in the car so as to avoid a repeat of what has happened. It doesn't necessarily need a failure of the VVC valve timing to initiate such things. It is feasible that the VVC was operating fine, and that the engine kept seeing det occur at high loads. With time, the incredible high pressures and temperatures involved in the detonation event will weaken the piston (usually either the crown or the edge) or one of the valves. Eventually, something gives up the ghost and the result of which you can see in your photos. If I were you, I'd consider running the proper ignition map for that type of engine. Good luck. Steve Swam in a deeper sea yesterday - it was horrible Link to comment Share on other sites More sharing options...
viperbl Posted November 3, 2008 Author Share Posted November 3, 2008 Cheers guys. Yes, I agree with Roger totally. It’s like a friend of mine who's valves hit pistons, they worked out the cam belt slipped. ok, but why did the cam belt slip? You do need to know the cause as well. I don’t plan on rebuilding this engine as I think its time for the move to duratec! Am I correct in reading that the duratec has a knock sensor location on it? I think I will get an external knock sensor and possibly fit an EGT sensor as well. My audi is full of these sensors and I have to say it does give you a better idea of how the engine is performing. Link to comment Share on other sites More sharing options...
Jason Plato Posted November 3, 2008 Share Posted November 3, 2008 the duratec doesnt have a knock sensor and then you would have to spend a fortune on an ecu that support knock and mapping adjustments. Your better off very simply getting the installation properly mapped with a reliable common ecu like an emerald, than to try and complicate things to overcome not getting mapped and then damaging another engine here is C7 TOP Taffia joint AO with Al Link to comment Share on other sites More sharing options...
Steve, Carol and little Cl Posted November 3, 2008 Share Posted November 3, 2008 I don't want to dampen your enthusiasm, but fitting a knock sensor is not as straight forward as it seems. Again, this sort of work normally involves a hell of a lot of development time. Knock sensors have to be able to clearly pick up the frequencies created by detonation, distinguish them from other forms of noise, and identify the cylinder accordingly. it usually takes about 1 to 2 weeks of full time test cell work to get the best position, and it has to be checked on other engines. Even then, there is no guarantee, as test have shown that sometime your det sensor "misses" one or two large cylinder pressure peaks. You then have to decide whether you take the risk and rely on your det sensor, or whether you trade off a bit of power and run a slightly more retarded spark so as not to go so far into det in the first place. I wouldn't want to risk several tens of thousands of pounds of car on my ability to guess at where the det sensor should be fitted. And, as Dave stated above, you would need to support your det sensor with the appropriate hardware in the ECU. How much would the ignition be retarded? How fast would the spark be advanced again to it's map setting? Do you retard all cylinders, or just one? What do you do if the average amount of spark retardation of a given set time is too high? What is too high? I think if you fit an external det sensor, then you are a very brave man. Steve No nappies at the moment, as I am at work Link to comment Share on other sites More sharing options...
dannylt Posted November 3, 2008 Share Posted November 3, 2008 Pretty sure the Duratec has knock sensors as standard, with the Ford ECU doing per-cylinder knock control. But I agree with the above - just map it properly to avoid knock and there's no problem? EGT might be useful as a safety limit on a turbo engine but surely a waste of time compared to spending time or money on other stuff. Link to comment Share on other sites More sharing options...
viperbl Posted November 3, 2008 Author Share Posted November 3, 2008 Oh, I thought they did have knock sensors? or was that only the 2.3 litre engine? I would not be putting in a knock sensors as some kind of substitute for a proper map!!!?? More for extra protection for if something goes wrong, for example, I am was not running any crazy ignition advance so it may have been down to low fuel flow or something like this, which could have induced knock and given crazy EGT’s. Now if I had an external knock sensors and EGT sensor I could have seen these move into the danger zone and done something about it, not so bothered about the ECU retarding ignition for me, as long as I know whats going on. Steve, you have a very good point there about the knock sensors, although I have been doing a bit of reading and there are some good aftermarket sensors that can do a good job. Of course, if there is not an actual place already in situ for the knock sensor, then fitting/drilling one myself is a road I don’t think I want to go down!! As for EGT sensor, I got thinking about this after speaking to a friend of mine about emeralds WOT changes, he said that this can cause high EGT’s. Link to comment Share on other sites More sharing options...
Jason Plato Posted November 3, 2008 Share Posted November 3, 2008 More for extra protection for if something goes wrong, for example, I am was not running any crazy ignition advance so it may have been down to low fuel flow or something like this, which could have induced knock and given crazy EGT’s. a fuel pressure sensor and alarm light would tackle the root cause ? what was the issue with Emeralds WOT changes ? and EGT ? here is C7 TOP Taffia joint AO with Al Link to comment Share on other sites More sharing options...
AMMO Posted November 3, 2008 Share Posted November 3, 2008 The Duratec does have a knock sensor. I remove them and just get the engines mapped properly as people have suggested. The engine when fitted to a Caterham has the flywheel, and sometimes pistons, rods etc. changed, plus the engine is mounted differently. The chances of getting the det sensor working correctly at a reasonable cost with a different ECU is remote. As understand it it is very complex as the sensor has to be specific for each engine and installation as it has to distinguish detonation from other engine noises. I haven't bothered to get involved with this and have not had any det problems at all, even with some quite powerful engines. Not something I lose sleep over. Ammo Raceco.com Link to comment Share on other sites More sharing options...
rj Posted November 3, 2008 Share Posted November 3, 2008 From what I know one of the few aftermarket ECUs that offer knock detection which actually works is the EFI - from Ole Buhl Motorsport. They are not exactly cheap though. Link to comment Share on other sites More sharing options...
viperbl Posted November 3, 2008 Author Share Posted November 3, 2008 a fuel pressure sensor and alarm light would tackle the root cause ? I plan to order one of them as well ;) or better still get a proper display that can monitor all these sensors for you! what was the issue with Emeralds WOT changes ? and EGT ? Not anything to do with just Emerald, more WOT throttle changes by retarding the ignition I believe, let me check with him and give you a proper explanation! Ammo, so they do have knock sensors ... yeah, but thats only half the battle I guess! Link to comment Share on other sites More sharing options...
John Vine Posted November 3, 2008 Share Posted November 3, 2008 The standard 1800 pistons will break if revved regularily above 7000k rpm.Blimey, is that right? As I recall, my old Supersport-R had a shift light firing at 7400 and a limiter at 7600, as set by CC themselves when they did the original SS upgrade. Was I (or the engine) living on borrowed time? JV Link to comment Share on other sites More sharing options...
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