Engine harshness under load

[Chris Edgar]

1962 4 door, 948cc.
All set up & running well..
except...

When I am driving up a gradual incline in top gear, with a light right foot all is fine & smooth, accelerates slowly.
However if I push the pedal down to accelerate & increase the speed, the engine becomes harsh & rough sounding, without seeming to speed up.
back off the pedal & it becomes smooth & quiet, accelerating slowly as before.
There is no audible pinking.

I am wondering if this is to do with the timing?
Dizzy is set for best idle (strobe shows about 8 deg adv. at 1000rpm, seems a lot, but is the is best idle speed)

I have just tried disconnecting the vacuum advance, (blanking off the carb. vac. inlet pipe) & it does seem somewhat better, but there is still a bit of harshness.

anyone any ideas?

thanks
Chris

[simmitc]

Check the compression on all cylinders. It could be a head gasket just starting to go, and failing when under increased load.

Also confirm that the air filter has the intake tube (the steel "silencer" in place, and that the exhaust coupling is not loose.

[bmcecosse]

What oil pressure does it have ? And keep the vacuum advance connected - but do retard the timing slightly - it may be detonating under load - which is dangerous. Also check the plug colour after such a run up the hill - white would suggest dangerous weak mixture.

[Chris Edgar]

Thanks both, for your replies

Can't give you oil pressure figures, no gauge...but the light goes out in 1 second & does not come on for a few secs. after the engine is stopped.

I will check out what you suggest...timing, mixture, plugs & compression

[Chris Edgar]

OK,
checked compressions, all c.140 p.s.i.
Plug colours are good
Air intake & exhaust connection good

Retarded ign. to about 5 deg. BTDC@1000r.p.m....
(does seem to wander a bit though...it's a fairly new 45D dist.)

Re-connected vacuum adv. pipe

Did not adjust mixture at this stage...only change one thing at a time!

Went for a run & it certainly does seem to pull smoother & more positively on the hills.

I will just continue to "monitor" how she goes.

many thanks
Chris

[bmcecosse]

I do suggest an oil pressure gauge asap........

[Chris Edgar]

Yes I know I should...

last 2 Minors I've had I have fitted oil (& water temp) gauges. Then sold the cars, still with gauges fitted.
Getting a bit tired of buying gauges!

But, yes you are correct & I will.
Soon.


cheers

[bmcecosse]

I did pick up a capillary temp gauge for mine ~ 12 years ago....still not got round to fitting it!

[JOWETTJAVELIN]

I did pick up a capillary temp gauge for mine ~ 12 years ago....still not got round to fitting it!

You fitted a vac gauge instead, didn't you? Admit it!

[bmcecosse]

Right next to the rev 'counter' and the clock........ I DO believe a temp gauge is very useful - just not quite got round to it yet.......

[MarkyB]

Define harshness, is it noise, or missing perhaps?

Spark plugs don't last for ever and do start to break down under maximum stress.

Why this has drifted into a discussion about gauges is beyond me!

[bmcecosse]

Because low oil pressure may be at the root of the 'harshness' - ie bearing clatter!