Try removing a spark plug lead, one at a time, while the engine is running
and note the sounds the engine makes. If the knock goes away or the sound
is reduced while the plug lead is disconnected then you have at least
located the cylinder that has the problem.
You could then attach a timing light to that plug (after reconnecting the
plug lead) and use the strobe flash of the light as a 'sync' to the noise.
If the noise occurs every time the light flashes then I would say the
problem is a rod bearing; if, however, the noise only occurs every other
flash then the problem would be in the valve train.
Glenn Mapes
gmapes@ball.com
1968 MGB
----------
From: John M. Trindle
To: MG Mailing List
Subject: Re: Knock Knock and Oil to Cam
Date: Thursday, November 30, 1995 10:44AM
On Thu, 30 Nov 1995, U. Goettsch wrote:
> On Thu, 30 Nov 1995, Frank van Dalen wrote:
>
> > I think you got it wrong John...
> >
> > Each piston has combustion once every 4 strokes of 180 degrees, ie once
every
> > two crankshaft revolutions. If there was a knock from one piston/rod,
you
would
> > hear it 500 times per minute at 1000 RPM, ie 500/60 = 8.33 times per
second.
> > The camshaft goes round at half the speed of the crankshaft, 4.17 a
second,
> > which is the frequency of the knock in question. Or have I gone mad?
>
> Mad, no, but read your post again - you contradicted yourself.
> cam = crank / 2, yes, but crank is 1000, not 500!
> => both rod knock and cam knock are 8 times per sec!
>
I'll grant you that I screwed up and ignition should occur in a cylinder
once every 2 crank cycles.
I'll even grant you that cam RPM is half of crank RPM. This makes sense
since the distributor fires a spark off for each cylinder as the rotor
goes around. If cam shaft RPM is 1/2 crank RPM this would correspond
with the previous paragraph.
I'll finally grant to you that I shouldn't have tried to answer this
question this week.
I still think it's a rod knock on one cylinder. The sound of a rod knock
can range from 'tick' up to YEEECATS!!!
Oh, now that I understand how RPM works in a 4/4 piston car, can you tell
me how it works in my RX7? <grin>
John M. Trindle | jtrindle@tsquare.com | Tidewater Sports Car Club
'73 MGB DSP | '69 Spitfire E Stock | '88 RX-7 C Stock
Home Page: http://www.widomaker.com/~trindle
"Remember, no matter where you go.... there you are. - Buckaroo Banzai"
|