Light knocking noise in the engine.

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Peter Cresswell
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Re: Light knocking noise in the engine.

Post by Peter Cresswell »

I would suspect that the damage to the edge of the conrod and the camshaft was caused by the debris from the dropped valve, possibly the broken off valve head getting between the conrod and the camshaft. I take it the dropped valve happened before you bought the car but it appears not to have done too many miles since the the piston and valve was fixed hence the marks on the conrod and camshaft still look fresh.
I too thought the conrods might be handed and this one had been put back together the wrong way round, but my experience of A-Series engines, which are handed, suggests that the conrod would not align correctly on the crank journal if that was so. Also it wouldn't affect the clearance between the edge of the conrod and the camshaft.
As to the 'light knocking noise', I must admit it sounded like a an MGB engine - at least like mine! But the metallic sound my engine makes is down to using spacers between the rockers rather than springs, and once it warms up it gets quieter. So I think you need to look further for the source of the noise. Have you taken the head off and checked the rocker shaft? Dropping a valve is a very violent occurrence with a lot of energy being dissipated in a very short space of time. Check the rocker shaft is ok and hasn't broken. Also check there are shims under pillar 1 and 4 which put a slight bow in the rocker shaft - BMC's solution to customer complaints of noisy tappets I believe.
One other thought - if it has dropped one of the valves are the other 7 just waiting to let go? Perhaps it's time to change them before they wreck another piston.
Pete
1969 MGB Roadster
2020 MG HS Exclusive
2007 Mercedes SLK
Plus 34 other cars since 1965
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Lakesailor
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Re: Light knocking noise in the engine.

Post by Lakesailor »

Ian Fozzard wrote: Sun Apr 18, 2021 6:34 pm It seemed to me that the rod/gudgeon pin fit was fine? Any looseness may be in the piston fit?
Ian F
Yes. That's was supposed to be my message in the video. The pin is a press fit in the little end of the rod. My suspicion is that the gudgeon boss in the piston is at the extreme of the tolerances and so moves across with a "clack" when the fuel ignites. The valve cut-out in the block allows the pressure to the top side of the piston to move it sharply along the pin. The end float of the piston along the pin is about 0.040".

The question is how to find a piston/pin pair with a touch less clearance.
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Lakesailor
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Re: Light knocking noise in the engine.

Post by Lakesailor »

Peter Cresswell wrote: Sun Apr 18, 2021 9:49 pm I would suspect that the damage to the edge of the conrod and the camshaft was caused by the debris from the dropped valve, possibly the broken off valve head getting between the conrod and the camshaft. I take it the dropped valve happened before you bought the car but it appears not to have done too many miles since the the piston and valve was fixed hence the marks on the conrod and camshaft still look fresh.
I too thought the conrods might be handed and this one had been put back together the wrong way round, but my experience of A-Series engines, which are handed, suggests that the conrod would not align correctly on the crank journal if that was so. Also it wouldn't affect the clearance between the edge of the conrod and the camshaft.
As to the 'light knocking noise', I must admit it sounded like a an MGB engine - at least like mine! But the metallic sound my engine makes is down to using spacers between the rockers rather than springs, and once it warms up it gets quieter. So I think you need to look further for the source of the noise. Have you taken the head off and checked the rocker shaft? Dropping a valve is a very violent occurrence with a lot of energy being dissipated in a very short space of time. Check the rocker shaft is ok and hasn't broken. Also check there are shims under pillar 1 and 4 which put a slight bow in the rocker shaft - BMC's solution to customer complaints of noisy tappets I believe.
One other thought - if it has dropped one of the valves are the other 7 just waiting to let go? Perhaps it's time to change them before they wreck another piston.
I think you are probably correct about the damage being historic.
The rods are marked 1,2,3,4 and the caps are punch identified so they and the rods are fitted as a pair and the right way around.
The rocker shaft is like new, pads not worn and shaft unmarked. The bushes in the rockers are unworn. As I understand it the shims (which are present) fit under pillar 2 & 3.

Image

The head is removed (see pics of the pistons). As the tapping seems to be half engine speed (I used a timing light to assess this) that would agree with the one piston moving along the pin on just ignition strokes. Pulling the HT lead when running was a bit inconclusive, but it did seem quieter.

My earlier suggestion that a mechanic friend could press a new piston on was a bit hopeful. I've seen some information about the process and it has quite a few pitfalls, if you get it wrong.

My tapping gets worse as it gets warmer. As I have stripped the motor and found nothing wrong, it wouldn't be a disaster if I rebuilt it and it still had the clacking noise. But it would seem like a waste of time and money.
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Lakesailor
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Re: Light knocking noise in the engine.

Post by Lakesailor »

I sent the piston and rod in question (No 1) to Jonathan at J&E Engineering in Lancashire (about 90 miles away) http://www.jandeengineering.co.uk/mg.html . He decided the little end was damaged. That is the piston was damaged where the gudgeon pin runs in the piston. He could see some marks on the end of the pin and has concluded that when the new piston was fitted to the old rod it was not located properly and had been repositioned with - probably - a drift and a big hammer. If you do it using the heat method you are just about * at that point if it does sit in the right place. Jonathan fits them using a press and a jig to position the pin far enough through the rod little end.
The only option you have if you used heat and got it wrong is to try and drift the pin back to the right place. This is how he thinks the damage has happened. He's sourced a new piston and a rod and has assembled them. Just waiting for the courier now.
So it was a little end rattle. Which is what I initially thought I'm still fitting a new cam and followers (when they get around to grinding it), and big end shells. (The mains are fine). I checked the almost-new oil pump, which is unmarked, but am leaving the cam bearings, as they are OK except for a little scoring on the front one, which isn't as bad as it looks in the pic. I've painted the engine black. I did try red, but it was too orange and a bit gaudy. I also did a lot of cleaning and painting in the empty engine bay, as it's easier than struggling with the motor back in.
I'm going to use cam lube and engine assembly lube as this engine had only done 120 miles in 4 years since a crank regrind. The bearing damage is, I am certain, due to 'dry' starts after oil drain down.

I hadn't really planned to have the engine out this year, but the tapping noise was something you home in on.

Update

Got my new piston and rod from Jonathan (which he had properly pressed on).
I got a new cam from Newman Cams followers, chain adjuster, and big end bearings.
With buckets full of cam lube and assembly lube I put it all together and spent the last 2 days sticking it back in the car.

Image

Following some of the advice on forums I filled the oil cooler by squirting oil in the supply pipe. I took off the oil filter so I could see when the oil got back to the filter base. I clapped a Mann filter on and kept squirting more oil in. I had inspected the oil pump and filled it with assembly lube. I filled the outlet pipe with oil and reconnected the oil cooler pipe.
With trepidation I decided to get the oil pressure up to make the best use of the priming. Three bursts on the starter of about 20 seconds (no plugs fitted) got oil pressure of about 60 psi. It is a hi-torque starter which I think means it is geared down so possibly doesn't turn as quickly as a direct drive starter.

Today I finished the installation, filled with water (just until I have tested it) and fitted the bonnet. It has been raining for days so I didn't want to attempt to start it until it was dry as the garage in integral with the house and don't want to stink the place out. It dried up after tea so I put the plugs in (after winding up oil pressure again).
Then "action". It started straight away. But a clattering noise was a surprise.

The bottom hose was too close to the (three blade) fan which was hitting it. A bit of loosening and twisting sorted that.
After about 5 minutes running at about 2000 rpm I decided to go for a gentle run (opinions are mixed on settling cams in. There is a new piston and rings and new big-end shells).
I live away from town so a gentle run at about 40/50 mph with undulating roads gave me a 10 minute run. Water temp good. Oil pressure a bit lower than before ( 70 psi on the go and 60 psi at tickover). I am using a different oil, Comma Classic 20/50 mineral oil, so it may be a bit thinner than the previous oil, which had been in the car for a while.

I didn't use very much throttle, but the car ran very smoothly, compared to before. Once I've attacked the tappets again it will be a bit quieter as well.

So far, no knocking.
Dave Wheatley
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Re: Light knocking noise in the engine.

Post by Dave Wheatley »

Fingers crossed all OK Phil.

Dave (islecastle1)
1978 MGB GT
1931 Austin 7 RM
1955 Standard 10
1972 Ford Cortina
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