Bottom end?

[philb115]

My syncro has become somewhat knocky on the bottom end – it has the usual tappet sound initially when cold, but that fades and a ticking or knocking persists from what I suppose is the bottom end. It’s worse when it’s cold, but can still be heard when idling and warm.

Any advice or diagnosis? Sorry to be so vague… I’ve got to do an oil change anyway, so I was going to take off the sump and have a poke around – any idea what I should be looking for (or if i’m looking in the right place at all?!)

[Chris S]

If you are going to do an oil change, please use either 15/40 or 20/40 oil, best of all is 20/50 if you can get it.
5/40 or 10/40 is to thin for our engines, and can cause the knocking that you describe.

[philb115]

Excellent – I’ve got 15/40 to go in there… also gonna do a filter change. No idea what is in there at the moment, though!

[philb115]

So… I changed the oil and filter, but I’m still getting a knocking / slapping at lower revs, even when the engine is warm. As I said in the OP, as is (relatively) normal the tappets tick when cold. Once it warms up it sounds smooth at higher (1000+) revs, but at 800 / 900 (idle, really) you can hear a knocking from the bottom end. A friend of a friend (an MOT mechanic) was over and suggested I get it looked at, as it’s “usually a sign of bad things to come”.

I’d like to sort it myself – I did the clutch in my previous syncro, so I’ve removed an engine before, but in this case I’m not quite sure what to look for – should I just take the sump off and look for bearing wear or something like that? I can’t find anything in the haynes that is at all helpful. If there is bearing wear, is it fixable with the engine in the car? I have a garage, but not that much space to work…

All help appreciated, as usual…

[Chris S]

With regard to bearing wear being fixable with the engine in the car, the answer is that it depends on how bad the wear is,

you may get away just with fitting new standard size shells, this is doable with the engine in the car,

If you can just fit new shells (after checking the big ends for ovality) I would check the oil pump while you have the bottom end open as I have seen Golfs with over 200,000 miles on them & no appreciable wear on the crankshaft, it all depends on the oil pump pressure

However if the crankshaft needs re grinding to take undersize shells then the complete engine must come out.

Does it knock on overrun? I.E. when the gearbox is in neutral & the engine is slowing down with no load? this can be a sign that the big ends are on the way out

[alexisblades]

Well worth getting one of these: http://www.ebay.co.uk/itm/CLARKE-CAR-MECHANICS-STETHOSCOPE-ENGINE-DOCTORS-/200357927289?pt=UK_Hand_Tools_Equipment&hash=item2ea6435979 to try and eliminate any of the less serious sources of the noise, before undoing big end bolts (they are stretch bolts and supposed to be single-use only).

Try disconnecting the fan belts and running the engine (for a brief moment!) to eliminate alternator/water pump/pas pump bearings.

Try depressing the clutch to eliminate worn clutch plate anti-chatter springs and gearbox input shaft bearings. Sounds like this can travel from one end of the engine to the other and cause a lot of confusion.

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