Really bad engine noise on over-run

[robby]

Right, where do I start.
Fully rebuilt engine, rebore, new pistons/rings, crank ground, new shells/thrusts, new oil pimp, water pump, rocker shaft, timing chain, everything. Anything else that was used (camshaft, followers etc) were cleaned and checked before assembly. I`ve built shedloads of these engines like this with no problem whatsoever. However, this one has come back for it`s 500 mile service noisy and whatever is wrong with it is a total mystery.

When stone cold, it`s fine, as it gets warmer, the noise gets worse. It does it when you rev the engine, but it`s far worse on over-run. I suspected a rocker shaft issue, that`s still as new, checked the tappets hot and cold, their fine. Removed the rocker shaft, pushrods and cam followers. As new. So, I stripped it suspecting a little end bearing. Nothing. Bores and pistons are still as new, camshaft as new all shells are as new too. rebuilt the engine and the noise is till there, it`s from the top end of the engine to the rear, as though it`s something on number 4 cylinder.

So, it came to stab in the dark time, I swapped the new cylinder head for a known good one with standard springs, seals etc just in case the new valve springs were too strong and snapping the valves shut loudly. Nope, noise is still there.

Removed fan belt, still noisy, checked the starter for sticking (it isn`t) and tried pressing the clutch to see if the noise changes. Nope still there.

So, I`m hoping someone here has had a similar noise and can shed any other light on it than I can.

The noise is best described as being like a lollipop stick in an old spoke bicycle wheel and gets louder the more you rev the engine

Cheers

Rob

[kennatt]

I had a very similar problem with an MGB after a rebuild,same noise when hot,and from the rear of the engine,turned out to be the distributor drive shaft,A ser engine has the same type of drive,would be worth having a look at yours,may be the same,its a part thats not very often changed on a rebuild because they very rarely wear,but a different one on the B cured the fault.Good luck

[bmcecosse]

Flywheel loose ? Have you tried running without the starter in place - start it with the handle - in case it's somehow fluttering against the flywheel... Exhaust not blowing at the manifold - or at the manifold/pipe connection - or touching the body shell ?

[bmcecosse]

That dizzy drive suggestion above sounds very plausible ! Certainly worth a try.

[robby]

I had a very similar problem with an MGB after a rebuild,same noise when hot,and from the rear of the engine,turned out to be the distributor drive shaft,A ser engine has the same type of drive,would be worth having a look at yours,may be the same,its a part thats not very often changed on a rebuild because they very rarely wear,but a different one on the B cured the fault.Good luck

Must admit, that crossed my mind, but dismissed it due to the noise being too high up, but I`ve got a couple of spare ones so it`s well worth a try, thanks

Flywheel loose ? Have you tried running without the starter in place - start it with the handle - in case it's somehow fluttering against the flywheel... Exhaust not blowing at the manifold - or at the manifold/pipe connection - or touching the body shell ?

No mate, it`s definately internal on the engine, I used my long screwdriver as a stethescope and the noise is worse around number four cylinder. Tried it on the bellhousing when I thought it might be a sticky starter. While I can hear it throught the bellhousing, it`s nowhere near as prominent as when the screwdriver is placed on the engine. I always puit a dab of loctite on the flywheel bolts as well as the locktabs. Thanks

[martin418]

hi did it have new cam bearings ? i had a rebuilt 2.8 ford v6 which had a similar noise and after a lot of investigation it was traced to a worn cam bearing ,

[robby]

hi did it have new cam bearings ? i had a rebuilt 2.8 ford v6 which had a similar noise and after a lot of investigation it was traced to a worn cam bearing ,

Yep new bearings fitted. I always get them fitted when I have the rebore done and I always check to make sure the oil holes are lined up before I take the block away. Thankyou though

[philthehill]

From what you have described it could be a broken crankshaft!

Possibly through the web.

I have known crankshafts to break and the car still drive.

[bmcecosse]

Me too - but the oil pressure goes to h*ll....

[philthehill]

Not necessarily - the oil feed to the rear of the crank is firstly to the rear main and then through a drilled passage in the rear web (and that is the web that usually goes) of the crankshaft to No: 4 crank pin journal. The oil pressure may reduce a little but oil leakage from the broken crank web will only replicate oil passing through No: 4 crank pin journal.
The last broken 'A' series crank that I dealt with the car was driven into the workshop and the oil pressure was reasonable; when the engine was stripped and the crankshaft removed it was found to be in two pieces and broken through the rear web.
If my memory serves me right BMC went through a period of major crankshaft failures due to poor production and quality control.

[robby]

Success. I`ve found and cured the problem. However, this can be used as a lesson in that the fault doesn`t always mean it`s where the noise is. The noise was distinctly around number four cylinder. No matter where I put the screwdriver stethoscope, the noise was loudest in that area.
However, on strip down, I found that the timing chain had thrown one of the rubber tensioners (Outer one). Changed the lot, new gears and chain and the engine runs as smooth as a wristwatch. There is no way on this earth I would have put the noise down to that given where the noise was coming from, but proof of the pudding is in the eating and cured it is

Happy days

Thanks for all the suggestions, I took them all on board as they were all viable options.


Rob

[bmcecosse]

Strange ! Well done finding it. Best bet by far is the Mini set-up with proper tensioner pad.