cskip Posted January 10, 2002 Share Posted January 10, 2002 I have a 1600 X-Flow in standard trim (no Rev Limiter). When reving the engine to approx. 5200 RPM the engine appears to hit a brick wall and simply will not rev higher. It does not act like a Rev limiter, the engine continues to rev smoothly at 5200 RPM. It has been suggested that this is caused by "Value Bounce". Is this possible and what is the solution? Could running the engine like this have caused any damage (e.g. Flat out in top gear down a long straight on the track)? Please go careful on me, I am not that technically minded!! Thanks in advance. Clive. Crossflow - Loud and Proud! Link to comment Share on other sites More sharing options...
Roger King Posted January 10, 2002 Share Posted January 10, 2002 Valve bounce is a general term for when the valve springs can no longer control the movement of the valves. The valves then no longer do what the camshaft is telling them to do and the effect is rather like a rev limiter. The simplest cause of this is simply that the valve springs are not strong enough to work at high revs, but you can also get a situation where the spring starts to resonate at a certain point in the rev range. In the second case you can often drive through the problem and the engine will run cleanly again at higher revs; this can be dealt with by changing the mass of the valve gear, using better damped springs, or using springs that resonate at a different point. I should point out that the above is simplistic, but gives a reasonable explanation. Both types of problem must be dealt with. It is also possible that you have a broken spring. 5200rpm is rather low for this to happen, even with a standard valve spring - are you sure the tacho is accurate? If it is accurate, is your engine as supplied by Ford, or is it a recon from an unkown source? If the latter, it is quite possible that dimensions such as spring height are incorrect or even that you have the wrong (or very tired) springs fitted. More investigation is needed. Link to comment Share on other sites More sharing options...
Big Brother Posted January 10, 2002 Share Posted January 10, 2002 Clive, Do you know the history of the engine or what cam you have? I ask, as my car (bought S/H with a 1700 SuperSprint lump) used to do this. Turned out it had been fitted with a 234 cam but with "single" valve springs. The solution was to fit double springs. (you need to fit spring new retainers too) These have completely transformed my engine. I have had to fit a rev limiter as its now way too easy to hit 7000rpmsmile.gif I'm not sure if this "bounce" could damage your engine - I guess it can't be too good in the long run. Steve www.Se7en-Up.co.uk id=limegreen> Link to comment Share on other sites More sharing options...
sjwb Posted January 10, 2002 Share Posted January 10, 2002 Most definately YES! Out of control valves can, and indeed do, contact pistons and or each other. Of course once they have kissed and locked then it's goodbye to to other major components. There is of course seat damage to consider. I am astounded that, if it is VB, you cannot discern it. Have you checked the ignition timing? Steve B Link to comment Share on other sites More sharing options...
STEVE GILBERT Posted January 10, 2002 Share Posted January 10, 2002 Just out of interest I changed all my xflow springs caps and seals without taking the head off and twas dead easy. If anyone needs to know how let me know. All.Knowing1@talk21.com Link to comment Share on other sites More sharing options...
philwaters Posted January 10, 2002 Share Posted January 10, 2002 Compressed air into one cylinder at a time to hold the valves up - well thats how we did Steve Mott's.. well I stood around a lot and watched anyway. Phil Waters 1600 X/flow - soon to be 2000 Zetec wink.gif Link to comment Share on other sites More sharing options...
MARK WARREN Posted January 10, 2002 Share Posted January 10, 2002 Clive,I presume that the throttle linkage is operating fully ? just a thought, try manually reving the engine. Link to comment Share on other sites More sharing options...
cskip Posted January 10, 2002 Author Share Posted January 10, 2002 Thanks all. A bit more info. about the engine may help. As far as I am aware the engine is completely standard as supplied with the car (1993) by Caterham (in kit form). It has not even had a unleaded conversion done! No rev limiter, Lumination ignition, Weber DCOE 40s etc. Not sure what cam is in use, but again presume that it is the Caterham supplied Cam. The engine has covered 9500 Miles and has been behaving in this manner since purchase Feb 2001 with 5800 Miles! Asked Arrowstar (from whom I purchased the car) at the time of purchase and was told that the Rev limiter was set correctly! (No further comment on that!) Roger - Really not sure if the Tacho is accurate. How do I test it? Mark - Good Idea will try and give an update. Clive. Crossflow - Loud and Proud! Link to comment Share on other sites More sharing options...
Roger King Posted January 10, 2002 Share Posted January 10, 2002 You can connect a digital tacho and compare with the one in the car. Does the engine do this in every gear? If so, it sounds like an engine problem. If it is only in top gear it may simply be aerodynamics. Link to comment Share on other sites More sharing options...
martynr Posted January 11, 2002 Share Posted January 11, 2002 If the engine is still using 'points' in the distributor try changing them. After a relatively short time the spring goes weak (especially if using high revs.) and allows the contacts to bounce on the dizzy cam effectively being a rev limiter. The best solution is to fit something like a Lumenition kit to the dizzy, it does not use points. Good luck Link to comment Share on other sites More sharing options...
cskip Posted January 11, 2002 Author Share Posted January 11, 2002 Roger - Sound like an engine problem then, as it does it in every gear! Clive. Crossflow - Loud and Proud! Link to comment Share on other sites More sharing options...
Barry Posted January 11, 2002 Share Posted January 11, 2002 Clive, when you press the accelerator all the way to the floor, does it fully open the throttle butterflies ? Link to comment Share on other sites More sharing options...
Graham Perry Posted January 11, 2002 Share Posted January 11, 2002 Would ignition timing scatter at high revs cause this ? Or perhaps the static ignition timing is way out ? Link to comment Share on other sites More sharing options...
bstark Posted January 11, 2002 Share Posted January 11, 2002 My car did exactly the same thing - right down to it being 5200rpm. It was originally a 1600 sprint but I had it upped to a 1700 supersprint engine when I bought it. The block was new but the carbs etc. were bolted on from the old engine. Once I had run it in, I found it flew up to 5200rpm and then just stopped revving. I assumed they hadn't re-jetted the carbs so I took it to a rolling road to get properly tuned. The basic problem turned out to be the ignition timing being way out, resulting in massive pinking at high revs. After the tune, the car seems fine - but it still seems a bit tight above 5000rpm (its done about 2500 miles on thenew engine). I hope this helps - I'm interested to hear about the valve springs, as my engine (built by Steve Parker Racing) shows no sign of racing up to 7000rpm. Bob Stark Supersprint first-timer Link to comment Share on other sites More sharing options...
chris a Posted January 11, 2002 Share Posted January 11, 2002 Bob, I have been reading this thread with some interest, because my 1700 doesn't pull as cleanly to 7,000 as I expected it would. 1st is OK but the rest seem to struggle to reach the top end. It has had several services, but never really improved, so I assumed that that was my lot. Until I read Bob's comment as my engine was also built by Steve Parker. I was going to look into the carb set up as I have still got 40's on and there is a thought that these might not be enough. Has anyone else got a similar story?? Link to comment Share on other sites More sharing options...
cskip Posted January 11, 2002 Author Share Posted January 11, 2002 Does anyone know if there will be a good source of info on this topic at the Auto Sport show tomorrow. Clive. Crossflow - Loud and Proud! Link to comment Share on other sites More sharing options...
Graham Perry Posted January 11, 2002 Share Posted January 11, 2002 Steves engines are normally pretty good, he has built me three excellent cross-flows over the years including my current steel jobby that has seen, ahem........ 10,000 revs on a few ocasions, so it might not be the mechanicals, more likely the carbs or ignition. Link to comment Share on other sites More sharing options...
JKJ Posted January 13, 2002 Share Posted January 13, 2002 I have a standard Caterham 1700 Supersprint, and was told, and feel, that the valve gear is "safe" 'till 6200rpm, so I don't think you should be looking for anything in excess of this, unless modified. Link to comment Share on other sites More sharing options...
bstark Posted January 13, 2002 Share Posted January 13, 2002 When the car was rolling road tuned, the final figure that came out was 120bhp at the wheels at 6000rpm, and at the Brooklands day I forced myself to use 6000rpm on the 0-60 runs, but the car just doesn't accelerate that urgently above, say, 5500rpm. It might just be a case of the engine still being tight and that it will improve once I have used these revs a few more times - I'm also used to Honda 16v engines which simply pull harder and harder the more revs you use (as opposed to the xflow which I'm guessing has a flatter curve, and certainly feels much torquier lower down) so it may be psychological now. I don't want to steal the thread but seeing that more than one person has mentioned this, what are people's experience of a 'standard'1700 supersprint? Do they love to rev to 7000? At what revs do they seem to be 'pulling' hardest? Bob Stark Supersprint first-timer Link to comment Share on other sites More sharing options...
Big Brother Posted January 13, 2002 Share Posted January 13, 2002 "Do they love to rev to 7000?" Well, since fitting the correct spec valve springs on my "standard" supersprint....yes! Mine starts to pull "properly" at around 3000 and the RR figures confirm this. The torque reading climbs slightly until around 6000 when it starts to drops off. The engine will easily rev to 7000rpm. As this is not recomended with a "standard" engine, I have now fitted a rev limiter (to keep my right foot in check) Steve www.Se7en-Up.co.uk id=limegreen> Edited by - steve motts on 13 Jan 2002 21:46:04 Link to comment Share on other sites More sharing options...
cskip Posted January 14, 2002 Author Share Posted January 14, 2002 What level should the rev limiter be set at for a 1600? Clive. Crossflow - Loud and Proud! Link to comment Share on other sites More sharing options...
philwaters Posted January 14, 2002 Share Posted January 14, 2002 I think the max power is developed at 6000rpm and I always used to keep mine set to around 6250-6500rpm. Don't really need to go much about 6000 as it starts to die off. Phil Waters 1600 X/flow - soon to be 2000 Zetec wink.gif Link to comment Share on other sites More sharing options...
Andy G Posted January 16, 2002 Share Posted January 16, 2002 I have a similar problem with my xflow, it used to rev quite freely up to 6250, then the silencer collapsed after an unscheduled through a gravel trap and after fitting the new silencer the highest it will rev to is 5950. I had been told the trouble would be sorted by tuning the carbs on a rolling road but after reading the above I am not so sure, any ideas. Andy G Link to comment Share on other sites More sharing options...
cdg Posted January 17, 2002 Share Posted January 17, 2002 I think you have to look at the whole installation in it's entirety. Many factors govern the way an engine performs. How well is the head ported? What camshaft are you using? How large are your valves? What choke sizes? What diameter are your primary exhaust pipes? What diameter is the internal pipe in the silencer? Any one of these factors(and many more besides) may influence your engines power output, which manifest's itself by it's ability to rev. under load. I wouldn't be too concerned about revving your x-flow to an early grave. In my experience even 180bhp screamers will give no more power after about 7000- 7500rpm, and are gutless below 5000rpm. "Supersprint" spec. engines i.e. 234 cam, decent big-valve head (albeit with fairly tame porting) 40DCOEs with 32mm (ish) chokes, will become breathless at about 6000, but will be very tractable at lower rpm. Surely this is where you need the power most for virtually all applications save out and out circuit racing. Chris. Link to comment Share on other sites More sharing options...
bstark Posted January 17, 2002 Share Posted January 17, 2002 Chris, That's what I wanted to hear! Frankly, on the road I haven't felt the need to use much more than 5000 - 5500rpm as the engine is so tractable. I was just concerned that there may be something wrong with the engine as it didn't give the impression of wanting to fly up to 7000 as a lot of people are suggesting. Bob Stark Supersprint first-timer Link to comment Share on other sites More sharing options...
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