Joined: Aug 2017 Posts: 96 Threads: 29
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My engine was rebuilt about 10,000 miles ago with new crank and bearings and has been apart a couple of times since to sort various things. I’ve just noticed a bit of rumbling, I assume from the rear main bearing. More noticeable in a basement car park with the bonnet up, not so audible outside.
How much rumble is acceptable? Should they be completely silent or is a bit of noise acceptable with roller mains?
I fitted a Ricardo head a couple of years ago and driven it fairly hard, (but not that far) since, including some hillclimbs and motorway thrashing. It’s a fairly harsh with the raised C/R and I imagine this isn’t great for bearing life.
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
29-05-2019, 10:43 AM
(This post was last modified: 29-05-2019, 10:50 AM by Bob Culver.)
Rumble is very influenced by spark advance. Any change makes a difference.
Compared with powerful motor cycles and others the bearings are generous. In ideal circumstances rolling bearings barely wear. Most bearing deterioration seems associated corrosion. I doubt if the loading makes much difference. Decades ago Sevens used for short runs, as many were, experienced rapid deterioration. Very many cars ran about very retarded to keep them quiet. I suspect modern oils (1960s on) have improved things considerably, but most of my experience has not involved much short cold running.
From vague recollection rumble when present is most obvious underway rather than idling. Depends somewhat on the advance characteristic.
The rear main is the usual culprit. May be loose on shaft. May be able to draw some conclusions by prising flywheel up and down and checking with a dial gauge. Presumably some interested repairer has recorded figures or hopefully will. Someone may be able to provide. .005"" clearance is not a lot in a plain bearing but significant for noise with a roller, although I cannot see how it does harm. (When very worn the crank can develop a sort of cyclic vibration)
Rumble might be some other factor; ie dynamo bearings.
Joined: Jan 2019 Posts: 1,567 Threads: 20
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Location: Bala North Wales
Car type: 1933 RP Standard Saloon
My RP's engine rumbles at the bottom end, even though I have recently replaced the rear main bearing (about 2K miles ago. When I had the engine apart to do this, there was no discernible 'rock' in the front mains and the big ends were all nice and tight with no apparent movement.
The rumble is not getting any worse. In fact, it seems to lessen as the engine gets warm. As the car is generally running well and reliably, and the oil pressure is always where it should be (between 2 and 4 lbs.sq.in.hot, using a good quality 10W/40 semi-synthetic oil), I am inclined to leave well alone at least for the time being.
Incidentally, the only Seven that I have driven that didn't rumble was a gem of a two bearing Ruby many years ago, which was a one owner and 60K miles from new example (When one still came across cars like that!)
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Location: Darkest Bedfordshire
What CR are you running that head at Tom? About 6:1 is 'enough' for a durable road car in my humble opinion.
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Location: Auckland, NZ
The Seven 2 brg engine is very suscepible. as I have mentioned before, into the 1950s my father used to change at least the rear main bearing about evry 2 years...considerably less than 10,000 miles. When sold a 3 spot tolerance one he reckoned it barely different from the old.
If there is a lot of scatter some igniton shots may be very advanced. The distr bearing main infuence. I dunno to what extent distr drive and timing gears contribute. Would not normally idle at full advance. A spring to take the slack out of manual linkage makes for consistent advance.
