Deep vibration / rumble on start-up
Discussion
Obviously I haven’t been out much in the car of late but she’s been in and out of the garage a few times as I’ve been cleaning, clawing, cleaning, waxing ( fist time and with great results!)
On start-up there’s a deep vibration/ rumble for first 30-60 seconds before she quietens down. It’s not a tappy manifold gasket sound, it’s not an alternator / pas bearing sound but something deeper and more rumble that sounds as if it’s coming from somewhere near the transmission. It’s more audible from inside the cabin and my concern is oil starvation and main bearings.....that or something hopefully far more innocent.
Generally she’s a healthy engine, new oil pressure sender suggests c50 psi, oil level good, oil only 9 months old (20-50 mineral) I,ve tried to capture the sound on video but it’s hard to discern.
Any thoughts?
On start-up there’s a deep vibration/ rumble for first 30-60 seconds before she quietens down. It’s not a tappy manifold gasket sound, it’s not an alternator / pas bearing sound but something deeper and more rumble that sounds as if it’s coming from somewhere near the transmission. It’s more audible from inside the cabin and my concern is oil starvation and main bearings.....that or something hopefully far more innocent.
Generally she’s a healthy engine, new oil pressure sender suggests c50 psi, oil level good, oil only 9 months old (20-50 mineral) I,ve tried to capture the sound on video but it’s hard to discern.
Any thoughts?
Steve_D said:
What time period between starts?
If it has been standing for some time it could be the hydraulic valve lifters bleeding down. So after 30/60 seconds they have filled.
Steve
The exhaust expands with heat, it could be as simple as that. The resonance will change as the heat increases If it has been standing for some time it could be the hydraulic valve lifters bleeding down. So after 30/60 seconds they have filled.
Steve
Thanks both
It’s say 2-3 days between starts so could be draining down but in truth it’s a very different sound to tappets.
The exhaust could be the source and if it is I’d be delighted. I Do need to re-fit the y piece as I don’t seem to be able to get a good seal around the piece/ manifold clamps ( any suggestions?) and when doing that I’ll check the bolt that attaches the main section of exhaust to the block for tightness etc (I remember it was a pig to re connect once I had removed the original catted y piece)
Thanks for the thoughts I’ll report back later
C
It’s say 2-3 days between starts so could be draining down but in truth it’s a very different sound to tappets.
The exhaust could be the source and if it is I’d be delighted. I Do need to re-fit the y piece as I don’t seem to be able to get a good seal around the piece/ manifold clamps ( any suggestions?) and when doing that I’ll check the bolt that attaches the main section of exhaust to the block for tightness etc (I remember it was a pig to re connect once I had removed the original catted y piece)
Thanks for the thoughts I’ll report back later
C
bobfather said:
Could be many things, I have a similar rumble that comes from the exhaust pipe. I has a resonance with engine movement that comes in at a certain RPM. Do you have a flexible section on your exhaust, these were fitted to break that resonance shake but not all Chims have them fitted
Whow! They did a flexible section? I'd be interested in looking into that a a retro fit, any pics out there.
during development they may of found issues that warranted its fitting 
Just a few ideas.
Deep rumble can be main bearings or big ends but tends to rumble on start up and continue to be there.
Your oil pressure reading of 50 psi is suspiciously on high side, have you/can you check that with a mechanical gauge ?
20/50 mineral oil is right.
How is your clutch operation, could it be clutch dragging at start up then as friction heats it up it expands away from the driven plate
Deep rumble can be main bearings or big ends but tends to rumble on start up and continue to be there.
Your oil pressure reading of 50 psi is suspiciously on high side, have you/can you check that with a mechanical gauge ?
20/50 mineral oil is right.
How is your clutch operation, could it be clutch dragging at start up then as friction heats it up it expands away from the driven plate
50 PSI cold oil pressure on a serp is normal in fact 55/60 not unusual thats on a functioning gauge of course 
and if its worn mains oil pressure hot idle OP will drop to nothing and the noise vibration should reappear 
I have my doubts its this , more than likely manifolds rubbing on the chassis top rails worth checking for sanity purposes inc Y piece outlet/down pipe as it passes diagonal tube behind radiator and before U clamp join to ex system
and if its worn mains oil pressure hot idle OP will drop to nothing and the noise vibration should reappear I have my doubts its this , more than likely manifolds rubbing on the chassis top rails worth checking for sanity purposes inc Y piece outlet/down pipe as it passes diagonal tube behind radiator and before U clamp join to ex system Edited by Zener on Wednesday 15th April 12:17
Thanks Frank, Simon
I’m obviously hoping it’s nothing to do with bearings and I’m comforted that the noise disappearing in less than a minute suggests this is unlikely
When I get the chance I’ll inspect the exhaust, y piece, manifolds for clearance..... looking back the appearance of the noise fits in with me fitting the y piece so hopefully nothing sinister.
The oil pressure sender is new and fitted only a month or so ago. It’s OEM (Caerbont) so hopefully not duff. The readings are 10 -15 psi higher than the old gauge before it packed up. Sadly I don’t have a wet gauge so can’t check. Anyone in MK got one I can borrow when we’re released from lock down?
I’m obviously hoping it’s nothing to do with bearings and I’m comforted that the noise disappearing in less than a minute suggests this is unlikely
When I get the chance I’ll inspect the exhaust, y piece, manifolds for clearance..... looking back the appearance of the noise fits in with me fitting the y piece so hopefully nothing sinister.
The oil pressure sender is new and fitted only a month or so ago. It’s OEM (Caerbont) so hopefully not duff. The readings are 10 -15 psi higher than the old gauge before it packed up. Sadly I don’t have a wet gauge so can’t check. Anyone in MK got one I can borrow when we’re released from lock down?
Edited by Macbags on Wednesday 15th April 16:30
My rumble appeared after I'd removed and replaced the exhaust to grease the propshaft UJs. I suspect fitting a new y piece may have changed the tension on your exhaust which could have caused your rumble. I never managed to get rid of my rumble even though I've since then fitted ACT manifolds and a Clive F Y piece. I can see the exhaust shaking as it reaches resonance.
Problem hopefully solved.
Un clamped the y piece and exhaust u clamp and noticed that the bolt connecting the exhaust to the engine block was extremely loose, so much so that I could undo it with my fingers. I suspect what was happening was the exhaust bracket was rattling against the block until such time as heat expansion in the exhaust and y piece created sufficient clearance/ tension?
All now refitted and bolt into block tightened quite firmly. Lets see what happens with the next few cold starts.
Incidentally there are two threaded holes in the block that are close to the exhaust bracket. I couldn’t nudge the bracket sufficiently forward to use the higher of the two holes. So have used the lower one...... is this correct or do i need to revisit, undo more of the system and nudge it all forward a centimetre or so ??
I’ll report back in a week or so
Many thanks for you4 help
Un clamped the y piece and exhaust u clamp and noticed that the bolt connecting the exhaust to the engine block was extremely loose, so much so that I could undo it with my fingers. I suspect what was happening was the exhaust bracket was rattling against the block until such time as heat expansion in the exhaust and y piece created sufficient clearance/ tension?
All now refitted and bolt into block tightened quite firmly. Lets see what happens with the next few cold starts.
Incidentally there are two threaded holes in the block that are close to the exhaust bracket. I couldn’t nudge the bracket sufficiently forward to use the higher of the two holes. So have used the lower one...... is this correct or do i need to revisit, undo more of the system and nudge it all forward a centimetre or so ??
I’ll report back in a week or so
Many thanks for you4 help
Macbags said:
Problem hopefully solved.
Incidentally there are two threaded holes in the block that are close to the exhaust bracket. I couldn’t nudge the bracket sufficiently forward to use the higher of the two holes. So have used the lower one...... is this correct or do i need to revisit, undo more of the system and nudge it all forward a centimetre or so ??
This is the position used on my 500. Hope it reassures you.Incidentally there are two threaded holes in the block that are close to the exhaust bracket. I couldn’t nudge the bracket sufficiently forward to use the higher of the two holes. So have used the lower one...... is this correct or do i need to revisit, undo more of the system and nudge it all forward a centimetre or so ??
Macbags said:
All now refitted and bolt into block tightened quite firmly. Lets see what happens with the next few cold starts.
On my old Chim' there was a thickish non-metalic washer on the bolt between the block and the pipe bracket, might have been tufnol. Dunno if this is the norm. Would be interested to know because the fixing bolt in question is missing from my Griff', on the job to do list.
lancepar said:
On my old Chim' there was a thickish non-metalic washer on the bolt between the block and the pipe bracket, might have been tufnol. Dunno if this is the norm. Would be interested to know because the fixing bolt in question is missing from my Griff', on the job to do list.
Never seen one on the exhausts I have removed and that's quite a few.Steve
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