TR7 engine knocking

[DragsterIOW]

Hi, I've got a problem with the engine on my 1980 TR7 DHC. I was driving along and it was running fine, and then suddenly it started knocking really loudly. I pulled over immediately, switched it off and trailered it back home. I've taken the sump off and the main bearings and big end bearings are all fine. There was a bit of play in the small end bearings, you could see movement between the piston and con rod but only very slightly, and all four had equal play. If one cylinder was like this and the others were fine I might have thought it was this. It seemed to come on so suddenly as well. There was no progression or slight rumble before hand - it was just immediately there all of a sudden.

I've also taken the cam cover off and all seems fine. The chain seems tensioned fine, from what I can see down from the top there's no sign of it hitting or rubbing anywhere, and the cam buckets also seem good. There's no severe wear on the cam lobes. I've checked if it's something simple touching the belts/pulleys etc but, again all seems fine. It still runs and fires as normal, so I can't see how the timing, valves etc could be at fault. I've also ruled out the gearbox as well because it still makes the noise with it out of gear, and with the clutch disengaged. It doesn't do it on cranking, only when it fires, which made me think it might be the starter, but you can hear that disengage when it fires and you get that whirring down sound, so I think it's just that it's not turning over fast enough on cranking to make the noise.

I've got a quick video of it so you can hear the knock.

 

https://youtu.be/Ye25VXVbPi8

 

If anyone knows more about these engines or has any idea what it could be, I would be very grateful, thanks.

[David James]

Hi - doesn't sound good. Have you done a compression test? Sounds as if it could be a badly slapping/damaged piston.

Just a thought to try first.

Regards

David

[Peter Cobbold]

Hi Dragster from IOW, and welcome to the forum.

The jack shaft that drives the water pump off the timing chain is a known weakness. But I've never heard one go.

Since the engine runs and that shaft drives the disy it must be turning OK - so maybe water pump has broken a vane or two??

More here:

http://www.tscusa.org/tech/WaterPump.asp

http://club.triumph.org.uk/cgi-bin/forum10/Blah.pl?m-1277758670/

Peter

 

On second thoughts after listening more it sounds too regular to be a broken wp.Maybe a dropped ev insert?

So....compression test next?

Edited June 13, 2015 by Peter Cobbold

[DragsterIOW]

Thanks David and Peter for your suggestions. I will do a compression test on it today and see if that sheds any light on the problem.

[DragsterIOW]

Right, did a compression test on it today, and all four cylinders were on the top end of the green zone on the gauge, around the 13 bar mark. I'm starting to think I might just have to strip the whole engine down and see what's revealed.

[David James]

Hi again.

It might be worth tying to locate where most of the noise comes from using a length of wood with one end placed against an ear and the other end placed on various areas of the engine to find the noisiest area. A form of stethoscope.

In the past I have had little success with this but you may be luckier.

Do be careful where you place the wood when the engine is running; H&S and all that.

Regards

David

[acaie]

It sounds quite harsh to me. My limited experience of bottom end problems is that the noise they make is not that harsh. This seems to be supported by what you found when you dropped the sump. So I suggest you have a really good look at the peripherals, and then take the head off first, before going to the trouble of taking the engine out to have a really good look at the bottom end. With the head off, it might become obvious whether one particular cylinder is causing the noise.

Good luck

Al

[Peter Cobbold]

Before stripping anything, try David's stethoscope idea on the the disy**. It might have thrown an advance spring and a weight is hitting the casing. I can hear that knock, quietly, in the first second of cranking, then it goes, and comes back louder when it fires. I agree with Al, it sounds superficial, not from deep in the engine.

Peter

 

** watch out for HT.

Edited June 14, 2015 by Peter Cobbold

[peejay4A]

Here's an off the wall suggestion. Could it be a badly cracked exhaust manifold?

[REPLIC8]

Have you checked it's not the alternator or the viscous fan making the noise? Easy to do by starting the engine with the belt removed. The bearings in the fan on my TR8 went all of a sudden and made an awful noise.

[Peter Cobbold]

Have you checked it's not the alternator or the viscous fan making the noise? Easy to do by starting the engine with the belt removed. The bearings in the fan on my TR8 went all of a sudden and made an awful noise.

I've heard the 2litre's viscous fan banging and it doesnt sound like the sound file. Its a sharper, more irregular hit and miss, 'clanging' sound. And its very obvious where its coming from.

Peter

[john 215]

Hi,

 

Have you tried pulling one HT lead off at a time ? By doing so you will decrease the load in that cylinder and may alter the ' depth' of the noise. The more info you can get the better before stripping. Sounds a bit deep but check the cam followers as they can go oval and valve springs as seen them break too. Difficult to tell but does the noise sound half engine speed or full engine speed ?

 

Just out of curiosity is your registration AMB ? ?

 

 

Cheers John

Edited June 22, 2015 by john 215

[DragsterIOW]

Thanks again to everyone for their help and suggestions. I managed to borrow an automotive stethoscope and listened to it pretty much all over the engine. I couldn't be specific with it, but it was definitely louder at the back of the engine. I also noticed that when you turned the engine over by hand, there was a stiff spot at exactly top dead centre of cylinder 4. This lead me to believe that it must be something to do with that cylinder. With the sump off, I took out the big end bearing shell on cylinder 4 and turned the engine over very slowly. There was now no stiff spot at all. This meant that whatever was causing the jam was thinner than the thicknes of the shell.

 

After figuring this out I got hold of an endoscope camera and looked inside through the spark plug hole. The first thing I noticed was a large chunk of the piston had cracked off on the top edge of its circumference. Poking it around some more showed some severe scratches and marks on the top of the piston. I also noticed some heavy scratches and pitting on the bore further up.

 

 

This picture shows the piston at the bottom, with the cracked bit on the top edge. The bore is directly ahead. You can also see the severe scratches on the piston to the bottom left.

 

 

 

 

This next one shows it slightly more clearly, although at an angle.

 

 

 

 

This next picture shows the pitting and scratches on the bore.

 

 

 

 

I also wanted to get the camera to point upwards towards the cylinder head to have a look at the valves and to try and see if I could see the peice that had broken off. The best I was able to get was a slightly sideways look at the top of the cylinder. You can see the head gasket running from top left to bottom right, with the cylinder head to the left and the bore to the right. This picture shows some of remnents of the cracked peices which have lodged themselves into the head. Again, also more marks and scratches.

 

 

 

 

This next one shows the exhaust valve to the left, with two distinct peices lodged into the head.

 

 

 

So, it looks like these peices broke off and flew around (making the sudden noise) before coming to a halt embedded in the head and causing the repetative knocking noise everytime the piston came up and smashed into them. It's remarkable they didn't get past the valves and smash the seats to bits.

 

It looks like it's going to have to be a complete stripdown and then assess the damage properly.

 

Also, in responce to John, yes it is Amber, sorry

[Peter Cobbold]

Causes? If the broken piston crown is under the exhaust valve then I'd suspect detonation. The sharp edged break too. If it were preignition it would look melted.The head gasket is sound - the compressions are good - then its unlikely to be hydraulic'ing.

Could the cylinder have swallowed a foreign object? ( butterfly over-run valve ?)

As the compressions are good you may well get away with a new piston.

I once holed three pistons on the 6 and got away with fitting new ones, with no bore work apart from a touch of emery paper.

Peter

[acaie]

Glad you've nailed it down. I guess the next decision is what to do with the bore damage, and can it be sorted without taking the engine out.

Good luck

Al

[john 215]

Hi,

 

Sorry to read the extent of the damage.

 

The engine in Amber is not the one she was born with, it was replaced with a second hand one by the previous owners boy friend, the original burnt nearly as much oil as petrol. Would check the inlet manifold for any debris, you don't want to start up a rebuilt / new engine only to suck something in..... seen that before !

 

Spoke to previous owner on Sunday and she often ask if I head anything about her old car, will keep this news quite until she is back on the road !

 

Cheers John

[DragsterIOW]

Hi everyone, sorry for the delay in responce. Got around to stripping the engine down the other day and finally worked out what had caused the piston damage. Turns out the piston ring had snapped right near the end, leaving a peice about 10mm in length. This had worked up and down, peening the top and bottom of the piston's groove until it eventually burst out of the top.

 

This was the view having just removed the head:

 

 

 

You can actually see the peice resting on the top of the piston towards the top left.

 

With the piston removed, you can really see the damage that occured:

 

 

 

This really explains why it came on so suddenly as well. As soon as the top of the piston burst, it was flying around smacking into everything. And because it was only the top ring that was affected, that explains why the compression was still good.

 

 

 

The damage to the head can also been seen:

 

 

It would seem that it didn't manage to get trapped between the valves and their seats, so at least there's some good news!

 

 

 

As for the damage to the bore, I think the endoscope camera magnified things a lot. On closer inspection, the scratches are very light, and hopefully with a good hone it should be useable.

 

 

So, I've ordered a load of bits from Robsport, and I'll have the head skimmed to remove any bits that are proud. Hopefully it shouldn't be too long until it's back on the road.