Clattering Sound On Overrun On Rebuilt Mi16 Engine

[Anthony 1,000]

Just a quick post to see if anyone has any suggestions for the cause of a nasty noise on a freshly rebuilt 1.9 Mi16 engine, done by a reputable engine builder, which I've fitted to a friends car for them.

 

The engine was a little rattly from the top end when it was first started, but this was to be expected given that the hydraulic tappets hadn't yet pumped themselves up and taken up the valve clearances. Sure enough, after running the engine on a fast idle for 20 minutes to bed in the cam, the top end had quietened down nicely as you'd expect.

 

However, there's a nasty noise coming from something subjectively around the flywheel end of the engine, more from the top end than the bottom from what I can tell. With the engine idling, there's an occasional single "clack" noise that occurs randomly every few seconds, that disappears when you give the engine some throttle and increase the revs. As soon as the engine is on overrun and coming back down the revs though, the clack noise returns and is much more noticeable, sort of a "clack-clacker-clackerty-clack-clack" until it returns to idle, as if someone has emptied a pot of bolts into a running food blender. The noise is pretty loud and very noticeable over the general engine din, and sounds like something is loose/broken somewhere, but I'm struggling to identify what.

 

I'm pretty sure that it's not a big-end issue, as that would normally be worse under load/revs and be a more pronounced, regular knock from the bottom end.

 

Oil pressure is OK, there's no smoke, and from a quick spin around the block, it seems to pull OK. The noise is present both with the clutch depressed and released.

 

Anyone got any ideas? I don't want to run the engine too much at idle as the rings need to be bedded in and hence I really don't want to glaze the bores. I'm assuming that the engine is still under warranty which I obviously don't want to invalidate, but by the same token I'm loathed to pull the engine back out again if I don't need to, and the car currently has no MOT (plus I don't really want to drive it for an hour without identifying the source of the noise)

[hcmini1989 16]

gearbox?

 

or diff/planet gears .jack it up while running and check the operation of the diff is ok.but if it does the noise while stationery it would`nt be the diff

 

does it do it when driving i mean in every gear including reverse

 

f**ked hydrualic lifter maybe .

 

possible flywheel loose ?and on the run down its chattering as it still carrying the momentum

 

 

 

sorry just ruling things out

Edited January 17, 2010 by hcmini1989

[Anthony 1,000]

gearbox?

 

or diff/planet gears .jack it up while running and check the operation of the diff is ok

 

does it do it when driving i mean in every gear including reverse .

 

f**ked hydrualic lifter maybe .

 

possible flywheel loose ?and on the run down its chattering as it still carrying the momentum

Gearbox is also rebuilt, although it hasn't been used before so it's not a known quantity. However, there's no other untoward noises like I would expect from a knackered gearbox and the diff seemed fine.

 

I'd expect a knackered hydraulic tappet to make the noise both under load and on overrun, whereas this doesn't - it's quiet (or atleast not obvious) if you hold the revs, hence not noticing it when bedding the cam in, but as soon as you let off the throttle it starts making this loud clattering/clacking sound until the revs fall back down to idle. It also sounds far more pronounced than a dead hydraulic tappet normally does.

 

A loose flywheel was my thought, but I would have expected the noise to quieten/change when the clutch was depressed, which it doesn't (or atleast not by any noticeable amount)

[hcmini1989 16]

wouldnt realy make a diffrence with the clutch depressed or not .as it would be the crank chattering on the flywheel .try a pry bar on the starter ring see if theres any noticable play . whil somone hols the other end for you

 

other than that theres nothing i can think off .bit off a tw*t really especially if you cant find what it is and have to pull the lot back out

 

you got a metal crack bar if so stick it on the block or gearbox etc and then too your ear you never no it might help

Edited January 17, 2010 by hcmini1989

[hcmini1989 16]

just thought of something else possibly the starter is it new or recon might be worth pulling it out just to check nothing has come a miss on the shaft and sliding into the flywheel .i know it would`nt explain why it does the noise only on rundown and idle .but im just giving you ideas and ruling things out

 

allso check for any marks on the flywheel i.e clean metal .

 

i would say check the clutch aswell but as you said it doesnt make a diffrence weather its depressed .does it judder at all ?

 

maybe pop the rocker off see if theres anything floating about

Edited January 17, 2010 by hcmini1989

[pugdamo 111 2 Cars]

Second the starter motor theory,well worth a check. Hopefully its something simple,nothing worse than doing a job twice

[B1ack_Mi16 67]

Maybe missing the locating dowel on the starter?

 

Had this on one Mi16 I owned some years ago, missing dowel, starter was touching flywheel teeth.

[Anthony 1,000]

wouldnt realy make a diffrence with the clutch depressed or not .as it would be the crank chattering on the flywheel .try a pry bar on the starter ring see if theres any noticable play . whil somone hols the other end for you

I'll give it a try when I'm next there, as it certainly sounds like a likely culprit. Need to whip the gearbox and clutch off to check it properly really, but if it's loose enough it'll show enough movement to wiggle with a pry bar.

 

just thought of something else possibly the starter is it new or recon might be worth pulling it out just to check nothing has come a miss on the shaft and sliding into the flywheel .i know it would`nt explain why it does the noise only on rundown and idle .but im just giving you ideas and ruling things out

I can't see that it's a starter motor issue and it didn't do it when fitted to the previous engine, but again, it's easy enough to rule out.

 

i would say check the clutch aswell but as you said it doesnt make a diffrence weather its depressed .does it judder at all ?

Clutch was new and feels fine - smooth, consistant engagement and no judder.

 

maybe pop the rocker off see if theres anything floating about

I'm reluctant to start pulling too much off the engine seeing as it's presumably under warranty, but if the other checks come up blank I'll speak to the person that built the engine.

[CosKev 16]

I had the 'clack' noise on my 8v every say 30 secs on idle,it was a nut floating round inside the cam cover

The cam was catching it and flicking it about

[GLPoomobile 958]

I'll be watching this topic as it sounds very similar to a noise mine makes (on the odd occasion it runs ). I've not noticed it from inside the car, but standing with my head under the bonnet, if I give it a rev and then let the throttle go it will make a clackety-clack-clack noise as it comes back down the revs, but only for an instant that it is in a certain rev range. Coming from the flywheel end of the head (sounds like the head, but could be coming from the gearbox I suppose).

[James_m 0]

Timing belt too loose and hitting the cover? I also get a noise like this which i think is the belt touching the cover when cold, but i leave the tension as it is as A it whines if its any tighter and B its been tensioned with the proper Peugeot siems tester and disappears after a few minutes anyway.

[Paul_13 212 1 Cars]

Engine moving and the exhaust/manifold is hitting something?

 

All engine mounts connected to block tight?

 

Spark plugs tight lol (my mate had this and it was making a horrendous noise!)

 

Bottom pulley tight?

 

Sounds silly but it could be anything.

 

I take it's Gav's motor?

[peakrevs 0]

gearbox?

 

or diff/planet gears .jack it up while running and check the operation of the diff is ok.but if it does the noise while stationery it would`nt be the diff

 

does it do it when driving i mean in every gear including reverse

 

f**ked hydrualic lifter maybe .

 

possible flywheel loose ?and on the run down its chattering as it still carrying the momentum

 

 

 

sorry just ruling things out

 

I too wonder if it might be the gearbox. I had just fitted a rebuilt n/a Cosworth YB and a newly built 4 speed Tran-X box and was appalled at the racket on the over-run. At first I thought it was engine and then the twin plate clutch. The engine and box came out several times in an effort to trace the noise and it was my engine builder who being familiar with that type of box said the noise was coming from the gearbox and that it was quite normal for a competition box. This was fine for racing but horrible on the road!

 

John

[Vili 17]

Clacking sound on overrun is typical symptom of worn big end bearing. It may sound that it's coming from the head, but it's still the big end.

I know it's recently rebuild, but these things happen.

Worth checking anyways.

[Tom Fenton 1,526]

You've probably already checked, but when my Mi made this noise once, it was one of the cam pulley bolts loose!!!! Luckily the cover was fitted so the bolt could not get out!

[boombang 2]

Had similar to you describe on an Mi16 with a bent valve guide on exhaust side.

 

Any history of cambelt snap or piston valve contact?

[KRISKARRERA 2 1 Cars]

This is all sounding very familiar. And of course my belt snapped in 2004.

[rallysteve 22]

Although not quite in the same league, my land rover made a terrible knocking noise on the overrun and it turned out to be the crank pulley had worked looks. Found it just whilst looking under the bonnet scratching my head one day!

 

Steve

[sorr 0]

Timing belt too loose and hitting the cover?

 

This is what mine did before I borrowed your (Anthony's) nice slender hands to tighten the belt.

[Paul_13 212 1 Cars]

Did you find out what it was Ant?

[Anthony 1,000]

I had manflu last week and been busy this week so I've not been over there to have a proper look at it yet.