knocking diesel

martyb2 · Post by **martyb2** » 08 Mar 2005, 20:09

Would burnt valves cause excessive diesel knock?
engine is from xantia, now in 306 xldt and the pump has been changed for the 306 unit, but its a real pain to start, and when it does start, it idles ok, but whenever you try to rev it, it knocks quite a lot, although it doesnt sound like a normal diesel knock, pump timing and valve timing seem to be fine, what can it be?

tonespeed1999 · Post by **tonespeed1999** » 08 Mar 2005, 23:21

possibly the fault lies with the mixing of wrong components,ie,camshaft,fuel pump and injectors.
sounds like youve got a timing/fuel problem.

Dave Burns · Post by **Dave Burns** » 08 Mar 2005, 23:21

Burnt valves wouldn't cause diesel knock to get any louder, quite the opposit since they would rob the cylinder of some of it charge under compression, burn valves will however give you starting trouble for the same reason.
A stuck open injector will make a hellish racket when the engine speed is raised from Idle, crack the injector unions one at a time to pinpoint the affected cylinder.
Worst case scenario would be a hot spot (swirl chamber) on the move, being mashed about by the piston, this or some other mechanical failing could be likely if the noise can't be temporarily stopped by cracking open the unions.
Dave

martyb2 · Post by **martyb2** » 09 Mar 2005, 01:45

I used the injectors and the pump from the original engine, and i ws told that it was running ok prior to it throwing a rod due to oil pump failure, I forgot to mention that it is a turbodiesel. Would a leaking manifold gasket cause any of these symptoms?

christi · Post by **christi** » 12 Mar 2005, 16:47

burnt valves cause difficult starting and clouds of smoke when running cold due to the lack of compression
a leaking manifold won't cause difficult starting, but it could make a noise
maybe you retard the timing a little and see it becomes quieter
also it could be a dripping injector
a missmatch of parts won't cause it to knock

rossd · Post by **rossd** » 13 Mar 2005, 00:15

A mismatch of parts could cause it to knock; if you replaced the pump but left the original injectors and those injectors have a lower opening pressure than the pump was designed for, the injection timing will be advanced and you will get knock [:)]

christi · Post by **christi** » 14 Mar 2005, 21:12

okay
would retarding the timing fix that?

rossd · Post by **rossd** » 15 Mar 2005, 16:05

Well it could do but then you will more than likely get smoke as the injection carries on past the optimal end of injection time. Best way around it would be to fit the injectors that the pump is matched too.