susser Posted February 14, 2005 Share Posted February 14, 2005 I've got a noise which I think is different to Bigfoot's. It goes like this; burble burble burble knock burble burble burble knock knock knock burble burble burble burble burble burble burble burble knock knock, and so on. It's a 1600 K Supersport, got a light flywheel, full race exhaust, done 20K and well cared for. I suspect the noise (Which sounds exactly like a diesel knock and not like an on load pink) is due to the EMS trying to get the timing on cue and being fooled by sudden changes in RPM such that the ignition pulse is arriving when it thinks it should but the crank hasn't got there yet. Then the microphone picks the knock up and retards the ignition by a few degs. This only happens when cold. Am I totally out of my tree ?? Link to comment Share on other sites More sharing options...
Myles Posted February 15, 2005 Share Posted February 15, 2005 Microphone picks the knock-up??? K's don't have a knock-sensor. Period. Project Scope-Creep is underway... Alcester Racing 7's Equipe - 🙆🏻™ Alcester-Racing-Sevens.com Link to comment Share on other sites More sharing options...
susser Posted February 15, 2005 Author Share Posted February 15, 2005 Well that kinda stops that theory dead in it's tracks. Another clue, it only does it when it's stone cold. It doesn't get cold enough on club nights, so no one in Carrotland has heard it properly. One concern; maybe I should warm it up at 1500 revs to keep those hydrodynamic bearings dynamic-ing. Link to comment Share on other sites More sharing options...
Jason Plato Posted February 15, 2005 Share Posted February 15, 2005 Justa bit of piston slap on warm up . Quite common on forged pistons when its cold -0 depending on your clearances . Does it disapear once the engine is over about 40 C ? Dave C7 TOP Powered by Hellier Performance 😬 South Wales AO Link to comment Share on other sites More sharing options...
wlegge Posted February 15, 2005 Share Posted February 15, 2005 Its not something stupid like the exhaust knocking something when the engine is cold and rocking slightly is it? My xflow when cold can sometimes just slightly move enough for the manifold to touch the body for a split second making a bit of a knocking sound. Link to comment Share on other sites More sharing options...
susser Posted February 15, 2005 Author Share Posted February 15, 2005 Dave Piston slap sounds about right, but it's unusual as it's not every stroke. Certainly dead sweet once it's warmed up. On a club night it doesn't get cold enough to do it properly. wlegge Thanks but I tried that. It's definitely internal. Link to comment Share on other sites More sharing options...
Mr Locust Posted February 15, 2005 Share Posted February 15, 2005 A known issue on Rover 25's etc. My understanding is that dealers are advised not to be concerned or take any action unless it persists for more than a certain time after startup without touching the throttle at all. 90 -120 sec seems to ring a bell. Our 40K/3year old Rover 25 1.4 used to do it a little bit. Ian Green and Silver Roadsport 😬 Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted February 15, 2005 Share Posted February 15, 2005 What is piston slap? - My Vx has developed something like this - but it settles after the car warms up. Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted February 15, 2005 Share Posted February 15, 2005 Looked it up - Dave, you might just have stopped me taking my engine apart again! Thanks Link to comment Share on other sites More sharing options...
Alex Wong1697456877 Posted February 15, 2005 Share Posted February 15, 2005 Piston slap sounds about right, but it's unusual as it's not every stroke. From what I've read, piston slap happens on the "bang" stroke, but not the compression stroke. Link to comment Share on other sites More sharing options...
Coose Posted February 15, 2005 Share Posted February 15, 2005 When an engine is cold there is a clearance between the piston and bore, the magnitude of which depends on the piston material and its rate of expansion. As the engine heats up, the pistons expand to take up some of this clearance. Piston slap is the sound a cold piston makes as it rocks in the bores before expanding, and occurs in both directions of stroke. Old japanese aircooled two-stroke motorbikes (Yamaha RD's for example) had a significant amount of piston/bore clearance, especially if 'Prox' pistons were used. They could sound like a bag of hammers until warm! One word of warning if your pistons are made of a 'high-expansion' material (requiring large piston/bore clearances) - warm the motor gently until up to temperature as 'cold seizures' are not unheard of. This is where a piston can rock to the extent that the edges of the crown or skirt can pick-up on the bore, causing it to smear..... We will mend it We will fix it... Link to comment Share on other sites More sharing options...
susser Posted February 16, 2005 Author Share Posted February 16, 2005 Alex, that's what I mean about not every stroke. I know it goes suck squeeze bang blow, and it desn't knock on any particular one, hence the original desciption of the relalatively random nature as described in my original post. If it was piston slap wouldn't it occur on every (bang) stroke like what it did on one of the pistons in my Volvo 340 after it had siezed. (we are talking a long time ago here). But it sounds as if it's searching for the correct timing, at least 'till it's warm. Edited by - susser on 16 Feb 2005 13:34:54 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now