HELP RATTLE FROM ENGINE

[mikchim]

can anyone help i recently bought a 1275gt(1971) that has been fitted with 998 cooper engine which apparently has been rebuilt.the problem is after driving for a short distance 5 miles or so stopped car restarted drove for 1 mile stopped and when driving off again engine started to rattle. on tick over sounds ok(no rattle) but rev counter reading very low and oil light on. when throttle applied light goes out and rattle starts .any pointers in right direction much appreciated

[miniman]

Oil pump? It's got plenty of oil in it, presumably?

[fwdracer]

Sounds like you've got very low oil pressure. If the oil light is going out as some throttle and rpm is provided, it is due to the oil pump spinning faster (hence pumping more) and keeping the engines oil pressure above the threshold that the oil pressure light comes on. Standard pressure switch is 7lb of oil pressure, which if the engine is run for any considerable length of time with this little oil pressure, an A-series or A+ will run it's Big End and Main bearings. You could fit an oil pressure gauge to see the engines oil pressure. Don't worry about the cold reading as it is artificially high due to the oil being thick. What you are interested in, is the pressure when the oil reaches normal running temp. A healthy A-Series or A+ should show about 35-40psi hot.

Does the knocking go when throttle is applied, and then reoccur when you lift off and the the engine goes into overrun? This is classic Big end knock.

[bikerkeith]

Many years ago I had oil pressure trouble with a 998 Mini. When the oil was hot the pressure sank to zero. The problem was the concentric oil pump had broken into pieces and the oil just flowed out through the gaps. Luckily I spotted the problem before any damage was done to the bearings, but you may want to check the condition of your pump.

[mikchim]

oil level is fine between min and max half way on dip stick,. sound appears to be coming from top end rather than bottom but not certain as difficult to id exactly but i have been advised that its possible that valve clearances may need adjusted as nut may be left slack after rebuild also been advised that dizzy is prone to moving on its own accord. on tickover engine sounds fine only on giving throttle noise starts .at time of problem starting car was carrying five people could this have added to cause of vault (valve clearance) when starting car with rocker cover off oil appears to travel up no problem does this mean pump ok .thanks for all replys

[Cooperman]

Low oip press and a 'rattle' when hot does sopund like big end bearings. However, with big ends going you usually get a 'death rattle' on start-up until a bit of thick oil gets around the journals.
Probably a strip-down of the engine will be the only safe thing to do. If it is the big ends and you continue to run it you'll very quickly damage the crank, which will probably need a re-grind anyway.
Thinking more laterally, maybe it could be a cam follower breaking up (unlikely), or a timing chain on its last legs, or a transfer-gear bush.
It's so difficult to tell without atually hearing and seeing the car running. Even then it can be difficult. I had a rattle and loss of power/poor starting from my Cooper 'S' a couple of years ago which I thought was a cam/follower problem and it turned out to be a broken alternator attachment lug on the engine front plate (hence the rattle) plus a squashed pipe on the lcb (loss of power/poor starting). This was after a rough rally. Two unrelated problems easily solved
Sometimes a noise seems to be coming from one part of the engine whilst, in practice, it's from somewhere else entirely.

[myname]

its not something daft like pinking is it...?

just a thought...