Deep knock at idle, any ideas?

badger · Post by **badger** » Sun Apr 22, 2007 7:04 pm

Hi gang. I'm not normally stumped by rover v8 engine faults - I've rebuilt enough over the years to have seen almost any failure mode anyone cares to mention, but this one's got me stumped!

Story so far:- I built and supplied an engine to a customer many hundreds of miles away (3.9, hotwire, serp. front end, non-std cam, mild gas flowing) to a spec identical to another engine I built a few years ago for a friend of his. (He liked it, so wanted the same!)
Called me to say that it was fine when installed (but took a long time on the starter to get oil pressure despite backfilling the oil cooler etc), all was fine during initial cam break-in at 200ish rpm, fine at idle as timing was adjusted, fine as he set off on a gentle 10 mile run round local roads, but knocking badly at idle on his return from this run!!!

He pulled the sump to check the main bearings, all were (in my opinion) fine for an engine that's just bedding in and starting to polish the high spots, but, convinced the knock was main bearings he fitted new shells anyway. Guess what.... it still knocked at idle but was getting worse, the noise not going away now until around 1200rpm!
I asked him to confirm the 4 torque convertor bolts were tight, and if possible to confirm the tightness of the 4 driveplate to flywheel adaptor plate bolts as well. He said all were tight. I asked again for confirmation about the latter 4 bolts when he removed the engine (proper access to them then, at least!), he again confirmed they were tight.
Engine was then removed and returned to me for investigation, at my request, under warranty.
I stripped the engine today - all main bearings are perfectly serviceable (clearances checked with plastigauge at 0.0025" big-ends, 0.002" mains) but slight scoring on the big-end shells. Crank is fine, it was dimensionally checked and polished (by a well-respected local engineering firm that I've used for years) prior to fitting. Endfloat is 0.006". All pistons are ok, no scuffing or sticky rings, no cracks anywhere, small-ends are good, no damage to rods, no witness marks anywhere internally (including sump pan!), basically I'm at a loss with this one.
Customer assures me the heavy knocking was coming from the bottom-end towards the rear, yet the driveplate has no cracks or damage either. Now, I've never ever heard a ZF4 automatic make a similar noise from the torque convertor, but is it possible to have a fault there with no adverse driving symptoms?
Now, I could easily have refused to take any part in this as he invalidated his warranty by breaking my seals and opening the sump up in the first place, but that's not my style. I pride myself on the reputation of my engines (most are used for hillrallying) and this is the first time I've ever had one returned for any reason

so I'm determined to get to the bottom of it.
If anyone out there has any ideas, please share them......

HairbearTE · Post by **HairbearTE** » Sun Apr 22, 2007 8:27 pm

The first thing I would do is run the engine on a test stand or in another vehicle that is known to be set up correctly. You can then be sure that it is the engine itself and not poor engine mounting/gearbox mounting/incorrect driveshaft angle/clutch issue. A mounting issue is one of the few problems I can think of that could be more audibly apparent at lower rpms than higher. From what you have said it dosent sound engine related, my money's on the set up causing the problem.

ppyvabw · Post by **ppyvabw** » Sun Apr 22, 2007 10:30 pm

Not the exhaust knocking on something, or exhaust baffles that are loose. Has he checked that?

GreenV8S · Post by **GreenV8S** » Mon Apr 23, 2007 12:08 am

Assuming you do check that the noise is coming from the engine itself, I remember hearing about a phenomena termed cam walk which can result in some very heavy knocking noises. As far as I remember it, the problem occurs when the cam has end float and moves so far that cam followers start catching on adjacent lobes.

RobertE · Post by **RobertE** » Mon Apr 23, 2007 1:00 am

ppyvabw wrote:Not the exhaust knocking on something, or exhaust baffles that are loose. Has he checked that?

Could be, we had a guy around here who was certain his rover was knocking... When we jacked the car up and turned it on, the sound disappeared. The noise was coming from exhaust knocking against the body.. and it was alot more apparent at low RPM's.

ppyvabw · Post by **ppyvabw** » Mon Apr 23, 2007 5:15 am

GreenV8S wrote:Assuming you do check that the noise is coming from the engine itself, I remember hearing about a phenomena termed cam walk which can result in some very heavy knocking noises. As far as I remember it, the problem occurs when the cam has end float and moves so far that cam followers start catching on adjacent lobes.

My engine knocks when i first start it but has done 18000 miles, and never done any damage. Good oil pressure etc..... and knocking goes after a second or two. Im always carefull starting it, just incase its slow oil pressure making the bearing knock. But...have also thought it could be something to do with the cam moving, but never actually knew wheter shuch a thing is possible. Presumably it's not a big problem is it? if it goes away ofcourse.

Would have expected damage after 18000 miles tho so im not worried.

Eliot · Post by **Eliot** » Mon Apr 23, 2007 6:07 am

HairbearTE wrote:The first thing I would do is run the engine on a test stand or in another vehicle that is known to be set up correctly. You can then be sure that it is the engine itself and not poor engine mounting/gearbox mounting/incorrect driveshaft angle/clutch issue. A mounting issue is one of the few problems I can think of that could be more audibly apparent at lower rpms than higher. From what you have said it dosent sound engine related, my money's on the set up causing the problem.

Yes - stick it on a stand or car - then you can be 100% certain.

badger · Post by **badger** » Mon Apr 23, 2007 11:42 am

Thanks for the replies so far, gang.
The owner assures me that it isn't a touch-point, mounts are good, as is exhaust (no rattles from cats etc). Had a good look at cam & followers - no signs of lifters catching adjacent followers, but if I remove the keeper plate and slide the cam back and forward in its bearings then that does indeed produce a deep knocking noise. I've checked the endfloat clearance on the cam (interim serpentine engine - crank-driven oil pump but fitted with a dizzy and a keeper plate on the front of the cam) with the thrust plate fitted and it's 4 thou, can't see that being an issue as it's within spec.
I must admit, I'm tending to think its an issue with his gearbox or torque convertor now.

ppyvabw · Post by **ppyvabw** » Mon Apr 23, 2007 5:38 pm

Whats his oil pressure like. If it was knocking like that, he would have poor pressure. He has put the right oil in it hasn't he, not 10w40 or something like that.

v8rob · Post by **v8rob** » Mon Apr 23, 2007 6:27 pm

badger we have a few like this over the years! recently we even had a new set of pistons that one was expanding around the pin more than the others! the only way i found this was putting the engine on our dyno and disconecting each spark at a time, if the knock goes away you are pretty sure it is little end, but when i stripped the motor everything was fine, i put the rod and piston in the oven and sure enough you could pull the piston up and down on the rod! other syptoms could be and dont take this the wrong way rod in back to front so it cant move doubtfull i know! but it happens. a follower that has a bad drilling for oil flow, fine when the revs pic up!,

badger · Post by **badger** » Mon Apr 23, 2007 9:20 pm

Hi v8rob, ta for the thoughts. The pistons came from a known good-running engine so I'm sure the noise isn't from them. It's too low down in the block and too "deep" a knock (apparently!) to be a follower, and it isn't totally rhythmic either! The rods were in the correct way round, I even checked the offset was correct with the dimple on the correct side of the rod just in case landrover had made a bad batch of rods with the dimple on the wrong side!

ppyvabw, it had the correct grade of oil (yes, 10 or 15W40, it's a serpentine). For a main bearing on a rover engine to make the noise described the shells would HAVE to have been down to copper to give the required clearance. As I posted earler, clearances checked with plastigauge on stripping, 0.002" mains and 0.0025" big-ends.

There may be light at the end of the tunnel though, my initial thoughts were a flex-plate issue but that all checked out ok. I've had another looksee at the ring gear, flex plate and adaptors this evening and the locating hole for the nose of the torque convertor (in the rear face of the adaptor block) appears to be slightly out of round, by 10 thou to be exact. Now, whether this would allow the torque convertor to knock against the adaptor when it's bolted solidly to the flex plate with only really fore and aft movement due to the "spring" of the plate, I don't know. Might be it though, certainly in the right area physically according to my customer.

ppyvabw · Post by **ppyvabw** » Mon Apr 23, 2007 10:48 pm

Its a serpentine? ohhhhh, i see. Didn't realise that they had different oil requirements having never had one. Ya learn suminc everyday. Yeah, just saying, if it was a main or a big end it would be un mistakeable.

When ya get to automatic gearboxes and torque converters and what hav ya, then im lost,

badger · Post by **badger** » Thu May 03, 2007 3:54 pm

Update:-
Engine checked out perfectly ok here. Replaced torque convertor spigot carrier (adaptor) on spec and sent engine back to customer. Engine re-fitted today - knock still there!!
My thoughts are now tending towards the gearbox or torque convertor(auto), as he assures me it isn't a touch-point or rattling catalytic convertor!
I'm 110% sure of one thing though - it isn't the engine!

ChrisJC · Post by **ChrisJC** » Mon Jul 02, 2007 7:09 am

Did this ever get resolved?

Chris.

badger · Post by **badger** » Thu Jul 05, 2007 3:06 pm

Don't know, is the simple answer! He was told/asked to pay for the gaskets used during the strip/rebuild, as there was nothing found attributable to my company. He agreed to send a cheque and I've never heard from him since!
My money is now on rattling catalytic convertor innards, and he just can't work it out for himself.