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68 Bentley T engine rattle under load.

3957 Views 104 Replies 12 Participants Last post by  Jim Walters
Hi all, I have been restoring my T1 5139 for the last 6 months and have completed the interior etc, however I have an annoying engine rattle under load which I cannot diagnose. L believe engine mileage may be 143k.

It feels like it is a collapsing hydraulic tappet, but all nice and quiet at idle or steady load or decellerating. I have had all the tappets out, tested them with the proper RR leak down tester and found 3 that would leak down very quickly at 2 seconds, 5 seconds and 7 seconds. Minimum should be 20 seconds maximum 90seconds. So the 3 weak ones were replaced with known good ones, put it all back together and the same rattle persists.

The noise is engine speed related, feels like it’s coming from the engine gallery area and is more like a hollow rattle than a knock. The noise increases if the load on the engine increases. It’s not the hydraulic brake pumps by the way. Those have been removed and the braking system has been converted to a conventional dual master cylinder and remote servos.

Would anyone have some ideas of where to look next? Weak valve springs? Cam looked good, no lobe wear.
Any assistance appreciated.
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Interesting thought re starter motor. Doesn’t feel like that but there is definitely something catching, metal to metal, gets worse when the engine load is increased. I have also changed the starter motor to a high torque one and the problem is still there.

re brakes. I used a Wilwood tandem brake master cylinder fitted where the original master cylinder was located. Think it was 1.75“ bore but would need to check. (Checked - twin 1 1/8” bore) This then goes off to two remote vacuum servo in the boot/trunk. Vacuum comes off a tapping on the inlet manifold. The servos are hidden behind a carpet covered panel, I lose some space but theres still loads of room. The brake lines then return to the rat trap and feed into the two circuits, one for one of the front brake callipers and the second for the other front brake callipers and rear callipers. The tandem master cylinder is fed from two separate reservoirs which in turn are fed from the existing brake reservoir. It all comes together and works fine with progressive braking and if I need to stomp on them they stop the car very well indeed. My choice to go down this route of course. Just couldn’t hack the malarkey of the original set up and it’s diabolical maintenance requirements.

I also installed 2psi residual pressure valves into both circuits to ensure brake effect is pretty much immediate when the pedal is depressed.
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Ps I know someone local to me that went for a tandem set up WITHOUT assistance, using a brake pedal box. Rock hard pedal and he has big muscles, but again even this stops his Shadow very well.
Thanks for the info - I was just curious. Sounds like you've done a really professional job there. Locating the servos remotely, as you have done, is the key to this mod - if mounted behind the master cylinder there is not enough ground clearance.
In post 23 I asked you to disconnect the drive belts to eliminate the fan clutch as the problem, just spinning it by hand doesn't tell you much unless the bearing in it is totally shot.

In this case the bearing is a little dry, but not binding.
The car drives well until you put a load on the bearing and gives you the noise you hear.
Stepping on the gas forces the bearing to move causing the problem.
When spinning as a mass, it's quiet until the bearing in the fan clutch starts to move.
The metallic sound is coming from the "chattering" of the bearing underload, and it's being transferred into the metal blades of the fan.
That metallic vibration sound is coming from the fan.
All this changes when the engine is cold and the viscus fluid is thick putting a load on the bearing _ at idle.

It's such a simple thing to remove the fan clutch drive belt(s), when compared to removing the trans; and all the other things you've done.

I would be surprised if it wasn't the fan clutch.
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I agree with Jeff, something in the front yard since you opened the back end and surely would have seen evidence of metal scraping. There is a short list of items that rotate up front and it's a process of elimination. A stethoscope will help. What moves? Water-pump, idler, P/S pump, fan clutch, some have an air pump. You'll find it.
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Thanks guys, I’ll run the car up with the individual belts removed, the sound appears to be from the back of the engine, but I take your point that if exaggerated by the fan blades it could be fooling me.
“loading“ the fan though? I don’t fully follow that, the fan is rpm related? free revving the engine is the same as loading the engine as far is the fan and clutch is concerned? Or am I missing something here. I only ever have the rattle when the engine is loaded.
I had to go into the backend anyway to sort the crankshaft oil leak and “whilst I was in there” a GM gearbox rebuild kit for £300 was too tempting. And fun to do myself.

Hopefully more updates tomorrow. And hopefully it’s something simple at the front end. The car actually runs really nice apart from the dreaded rattle!.
If the vicus coupling is engaged, then things remain quiet, but it may and does slip on acceleration against the fluid.
When this happens the internal bearing rotates independently from the pulley speed.
In your case the bearing has become dried out and makes noise and vibration _ the vibration is amplified in the metal fan blades.
So my theory goes.

How Does a Viscous Fan Clutch Work? - YouTube
Update. Removed all the drive belts individually.
The noise/rattle is still there…so it’s not the air con compressor, power steering pump, coolant pump, viscous coupling, fan, alternator etc.

haven’t managed to get a second person to assist yet. Next plan is to replicate the rattle and try to pinpoint the location a bit better. Probably whip the rocker covers off when we test which may help to locate the problem. Ah the challenge continues! To add to the woes one of my rear shock absorbers has decided to push through the bottom mount on the trailing arm. So out with the welder and in with a new cup mount from IntroCar. These cars are fun aren’t they.

Shame really as it does drive really nice when it’s not rattling.
Make sure the replacement cup has a drain hole and it is oriented to properly drain.

It is possible you have a broken rocker arm spring that is causing your rattle issue which can easily be verified once the covers are off.
Ok thanks will check when I fit the new one.
Eye Vertebrate Automotive tire Jaw Organism
Wheel Tire Automotive tire Vehicle Tread
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Metal prep is everything here I noticed the rear supporting member was used as a jacking point during it's life rather than the differential case itself. The member is sheet metal that is spot welded and filled with foam and held to the body with 2 bolts so it is not a desirable spot to lift. The workshop manual makes that clear.
Good luck with the repair.
yes, seems they missed the differential as the jacking point. I am undoing 54 years of bodges on this car…
Bloody Hell !
I would have bet good money that it was coming from the front end, specifically the fan clutch.
I still think it's superficial rattle coming from a heat shield or something like that.
It sounds too much like a thin metal metallic sound to be coming from anywhere else such as under the valve cover.

Valve train sounds (from my experience with many cars) are "all the time" and of ticking sounds, not intermittent metallic rattles.

Given that the rear spring pocket has let go, I would look for other places under the engine bay where some metal has rusted through causing the noise.
Given the fact that the noise only happens under torque _ something is shifting to cause the rattle when the engine moves under torque.

My new theory anyway.
On second thought......As discussed/posted earlier and after additional thought, I would place my bet along with Jeff regarding the fan clutch. It will usually sound fine until it is under load via the belts and does produce a screech. Valve train noise as I suggested would have a different sound signature altogether, but since you are removing the valve covers, it would not hurt to poke around a bit. You will eventually find the culprit.
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He said he removed all the belts individually; I'm going to assume that when the fan belt was removed that he revved the engine sufficiently to where the rattle would have occurred.
Totally agree on the valve train noise having a different sound signature.
Hi, yes I removed all the belts and ran the car up the road. Same noise as before.
If the car is in park, and you rev it, does it do then, and is the car fully warmed up or from a cold start, or does it matter ?
Revving in park does not creat the rattle. Only in drive on the road, or loading in the engine in drive with the brake depressed. It will be quiet for the first few minutes as the car warms a little, and then starts to rattle under load. It never rattles whilst decelerating or coasting or lightly loaded.

My head is telling me it’s a tappet failing, maybe my phone exaggerates the noise to be more tinny than it is. It’s a hammering noise relative to engine speed (it could be double engine speed but hard to tell). It is not a main bearing rumble, I have had that before on a different car and it’s not that. When the rattle starts, putting more load on the engine makes the rattle louder and at its worst it becomes a continuous graunching noise. Getting off the gas eradicates the rattle/noise.

Whilst my head says tappet I am struggling to see how that would be engine load related. There should be no extra load on the tappet when engine is loaded compared to when engine is free revved. Only other thought is it’s relative to air/gas flow through the engine. I Borescoped the engine cylinders and didn’t find anything alarming. Maybe some minor foreign object damage on one piston. It’s not coming from the exhaust manifold or system. Given I haven’t found it yet from various inspections/tests it feels like it is going to be something odd. Thanks.
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I had similar symptoms when the transmission oil level was low. I think the rattle comes from cavitation in the torque converter. I assume that the noise transmits through the whole engine/transmission unit and appears where the acoustics are right. It took a few minutes to cure itself after topping up the Dexron.

Alan D.
Hi, just checked the transmission oil level and it’s fine. I did rebuild the gearbox and replace the torque converter for a service exchange unit from flyingspares whilst fitting the crankshaft lip seal conversion. Noise was present both before and after this work. No evidence of any damage within the gearbox when it was stripped and rebuilt. Thanks.
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