25 replies to this topic

[Nelson92]

What does valve bounce sound like?

http://www.youtube.c...feature=related

ugly. go to tescos 10pm on a saturday and someone in a saxo will show you.

[Ethel]

I doubt you'd hear very much over the general racket of a thrashing A series. Basically, the engine is turning so fast that the springs can't push the valves closed quick enough to keep them in contact with the cam so the valves close too late and, because they are effectively free the springs can start to resonate so they don't keep the valves pressed shut. The power just takes a rapid power dive in a wet fart stylee - hopefully, it'd make a much nastier noise if it managed to shake the valve collets free.

I'd think your problem is more likely to be ignition related, try and find a Crypton tuner or borrow a timing strobe. Points, condenser, dizzy cap or coil may be to blame or you may find you need to strip and service your dizzy centrifugal advance.

[mini7boy]

What does valve bounce sound like?

speaking from experience with it in a Mini race engine, you get a terrible misfire that gets worse with increasing RPMs to the point where the engine just won't run any faster.
On mine, it started misfiring audibly at about 6,000 and absolutely would not rev beyond 6,800. All I did was replace the springs and it would rev past 7500 with no problems and
with much increased power from about 6000 onward.

Valve springs are cheap, so there's no excuse for prolonged running with inadequate springs and taking a chance on bouncing a valve off of a piston. Just make sure to get a good valve job done
while the head is disassembled

[jaydee]

I'm agree, and double springs are a must have on every tuned a series.
Valve bounce its very dangerous for engine health, i've seen pistons smashed by a bounced off valve.

[m1tch]

Yeah, thats the fella obviously I never red line the thing day to day, im not a chav lol But yeah it sounded like a rev limiter....but I then thought..ah lol no electronic ignition/fuel cut lol so can't be lol Mine not misfiring, maybe the mix it too lean? (no I don't want large flames out the back lol) How easy would double springs be to fit? Im guessing its a head off job? Im guessing I would need new collets as well?

Edited by m1tch, 12 July 2009 - 08:23 PM.

[Saxo-Fiesta-Mini]

wondered why my old saxo made that noise. The next owner who thought 6.5kpm in 2nd gear was clever then this noise resulted and he came over to my work and told me the gearbox giving up was my fault if u saw how that car was driven the weeks b4 hand

to be honest breathing and a free flowing exhaust are the first limitations, then head and cam, then ignition, then compression ratio, then balance the engine, then forced induction ect

[m1tch]

ah ok, hmm well im going to have a 1275 with a 1100 sprint box put in at some point (when I get round to building it lol) so I just need to get my 998 running at optimum to keep up with modern traffic really. The engine has done 74k miles from new, partly ported head at some point, head hasn't been taken off in about 2 decades lol at least its only a few bolts on mine would it be worth changing to the double springs? the ignition system is basically new, would a lean setup cause this problem?

[Saxo-Fiesta-Mini]

to be honest with a 998 id just wip the head off clean the valve face, seats and decoke the ports and combustion chambers.

then rest the valve gaps, fresh oil, plugs, filters, coolant and then stage one kit other than that not really worth it when compaired to the jump of a 1275

[m1tch]

to be honest with a 998 id just wip the head off clean the valve face, seats and decoke the ports and combustion chambers.

then rest the valve gaps, fresh oil, plugs, filters, coolant and then stage one kit other than that not really worth it when compaired to the jump of a 1275

yeah im just maintaining it and getting it running just so at the moment, I know there is no point throwing money at it, on a 998 its not worth it as I will be putting a 1275 in there, just making the car more fun lol considering it was running on 3 cylnders, has a dodgy MOT and was condended as 'dangerous' after the first MOT, I have now got it all running well, shell is spot on now (its been welded enough to me a mine sweaper lol)

Im just trying to get my mini to rev as it should really, feels a bit sluggish at reving, although my other car is an RX7 that if it had lightened internals could rev to 16k lol

[bigmotherwhale]

if you want to decoke your engnine get some distilled water and spray it into the intake with the filter off, at a good heathy rpm, you will be left with a pile of carbon at the exit of the exhaust.

[m1tch]

Just gotta be careful of hydro-lock with that one lol