The following warnings occurred:
Warning [2] Undefined variable $search_thread - Line: 60 - File: showthread.php(1617) : eval()'d code PHP 8.1.27 (Linux)
File Line Function
/inc/class_error.php 153 errorHandler->error
/showthread.php(1617) : eval()'d code 60 errorHandler->error_callback
/showthread.php 1617 eval




Thread Rating:
  • 1 Vote(s) - 1 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Mysterious knocking
#1
Thumbs Up 
Just finished my first overhaul of an engine, not a full rebuild but new main bearings, new piston rings, wrist pins, little end bolts etc however there's a slight metallic knocking noise now the engines all back together, at idle it's nice and smooth, same goes for high revs however when the throttle is opened quickly the knocking happens until the rpm evens out, it doesn't do this to any noticeable amount when pulling up a hill or accelerating when in the car.

Just wondering if anyone had any experience with this, all bearings had some degrees of tightness, not tight just a tad stiff so no rod knock that I could imagine, same goes for the little end, they had literally no play at all and the new pins weren't tight just slightly stiffer than the old ones.

I hope it's nothing for concern.
Reply
#2
Is it a 2 bearing crank? If so is it a new steel one?

I had an initial problem with the crank touching the centre housing for the camshaft bearing.
The crank apparently whipped enough to take very fine slices of aluminium from the housing.

Another answer could be that if you fitted your old flywheel to a new crank that the taper was not lapped enough or the crank nut tightened up enough.

This makes quite a heavy noise.

Regards

Bill G
Based near the Scottish Border,
Reply
#3
Bill, I think this is a big seven.
12, poss piston knock, were the bores honed, I think you made ref to a wear ridge how was that dealt with?
Are the pistons back in the right way round ie split to non thrust side.
Is the ign timing a tad over advanced.
Small end bolts tightened?
Reply
#4
Out of curiosity how would the pistons being the wrong way around create any knocking noise?

Little end bolts tightened down and loctite used on the threads, I've tried retarding the ignition timing with no effect.

The wear ridge was removed by hand with a fine file over several hours.
Reply
#5
(02-11-2020, 08:08 PM)12jslater Wrote: Out of curiosity how would the pistons being the wrong way around create any knocking noise?

You would get piston slap. However, I suspect that the noise you refer to may very well be timing a bit over advanced. I have no experience of the Big Seven engine, but, as a starting point, I would set the static timing at top dead centre and see how you go.

On my RP having set the timing up, I always end up fine tuning it on road test! But then the parameters for sorting the timing out are probably a bit different.
Reply
#6
I am not familair with the Big 7 but on other makes a loose front pulley gives these symptoms. (In a small Seven a loose flywheel!) Accepted "'modern"' (post 1930s) practice is that no bearing should rub, and certainly not shells, but with white metal often OK..
Reply
#7
(02-11-2020, 06:09 PM)12jslater Wrote: however when the throttle is opened quickly the knocking happens until the rpm evens out

I'm afraid my experience of this type of noise suggests that it is usually related to big ends. At the moment it is minor but it may get worse.......
Reply
#8
Didn’t like to say, but was a bit concerned at stiffness in the bearings, there shouldn’t be stiffness in new shell bearings.
Might be an idea to pull the sump off and have a look at the shells.
Reply
#9
We always said 'turn up the radio'  Big Grin
Reply
#10
I'll have to drop the sump today, just for clarity how exactly would having the split skirt on the wrong side cause piston slap, I assumed it would just make the piston more vulnerable to failure.
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)