420GSi tourer engine vibration

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Stan Thomas
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Re: 420GSi tourer engine vibration

Post by Stan Thomas »

Hi Mathew,

Given a "T" Series petrol engine should be turbine smooth at 3-4000 rev/min, so here goes with my two-pennyworth.

Firstly, the mass of the crank assembly and the speed at which the vibration occurs ostensibly rules out an ignition or fueling problem, as this would show up as a general fall-off of power. That said, and as already been suggested - merely revving the engine in neutral to within the rev-range at which the phenonenon occurs will provide verification or otherwise.

Next, turn to engine mountings. In this respect first examine the condition and tightness of the torque reaction stay assembly bolted to the top of the offside front wing. The problem here is that this may not show up as the culprit with revving the engine off load - and that goes for the condition of the other engine mounts. The next port of call is the vibration damper on the front of the crank - although I have to say I have never known one to give trouble on any vehicle in all my years. In simple terms it is a small rubber-mounted flywheel which absorbs any crankshaft natual harmonic reonance (i.e. same as a glass vibrating when you play a piano)!

That you say the problem does not arise at slower speeds in a lower gear tends to eliminate anything in the drive train such as drive shafts and wheel bearings - but a simple check out would not be out of place.

There remains of course the possibility of wheel balance although again I doubt this because such incidents usually manifest themselves by a shake in the steering - but if you are exploring drive shaft etc, with the wheels off it might be worth changing the front ones to the rear.

The reality is however, I'd really need to experience the vibration first-hand to get closer to the solution and its a pity you are not nearer to me in Stafford - but keep us posted!

Ring me if you feel I can help further on 01785 713862.
itcaptainslow
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Re: 420GSi tourer engine vibration

Post by itcaptainslow »

Stan Thomas wrote: Fri Jan 12, 2024 7:26 am The next port of call is the vibration damper on the front of the crank - although I have to say I have never known one to give trouble on any vehicle in all my years. In simple terms it is a small rubber-mounted flywheel which absorbs any crankshaft natual harmonic reonance (i.e. same as a glass vibrating when you play a piano)!

Quite a common failure point on the BMW sourced diesel in the ZT/75, and we had a fair few let go at Vauxhall & Citroen (Relay vans being a particular culprit). I didn’t realise the T-Series was so equipped, mind!

It’s worth a check being as the car has one, although as Stan says, it’s unlikely, and if it had failed, I think you’d hear it at a wider range of RPM, including at idle.

Stan - I’d PM your number to Matthew rather than post it on an open forum, which is ripe to be harvested by bots.
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MatthewL
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Re: 420GSi tourer engine vibration

Post by MatthewL »

Hi Stan - thank you - that is really helpful. The engine pulls smoothly with no flat spots, generally sounds great and as you say, is otherwise turbine smooth. Tried car at 3500 revs in 3rd and it was nearly as bad but as you say, the car wasn’t under load. I think this does sound like the mounts as everyone suggests. Now time to find them. I might well give you a call Stan. Thanks for the kind offer. Matthew
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GTiJohn
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Re: 420GSi tourer engine vibration

Post by GTiJohn »

These are the engine mounts on a T-series R8


Image


They differ from the mounting system in the HHR 420 that Stan is referring to. You still have 2 tie bars (21 and 25) but these are both behind the engine. Bad vibrations caused by a failed mount 'mass carriers' (5, 10 and 14) are likely to be more than at one specific frequency, i.e. much more noticeable!

You could have one of the tie bar bushes fail but these are difficult to see without a ramp.
I like Twin Cams.... and Single Cams...and now Turbos
Stan Thomas
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Re: 420GSi tourer engine vibration

Post by Stan Thomas »

I did not know your car is an R8 as mine is an HH-R, although the principles discussed are the same, just diiferring componentry which does the same job.

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MatthewL
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Re: 420GSi tourer engine vibration

Post by MatthewL »

Thanks John and Stan too! I think I’ve seen the one marked 10 for sale (KKB101890 I think) but 5 and 14 seem harder to find and I’m not sure if the part numbers. If anyone knows then it would be a great help!
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GTiJohn
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Re: 420GSi tourer engine vibration

Post by GTiJohn »

MatthewL wrote: Fri Jan 12, 2024 5:55 pm Thanks John and Stan too! I think I’ve seen the one marked 10 for sale (KKB101890 I think) but 5 and 14 seem harder to find and I’m not sure if the part numbers. If anyone knows then it would be a great help!

5 and 14 (and 10) have been NLA for some time. They're close to top of our list for remanufacture.

(Stan, Matthew says it's a Tourer, so it must be an R8 :wink3 )
I like Twin Cams.... and Single Cams...and now Turbos
Stan Thomas
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Re: 420GSi tourer engine vibration

Post by Stan Thomas »

Sorry John, I should have remembered the tourer is an R8. The problem is I must be going senile - I'm even sending letters to myself to check I've posted them!
MatthewL
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Re: 420GSi tourer engine vibration

Post by MatthewL »

Comes to us all Stan! I can watch the same tv series over and over and enjoy them like it’s the first time I’ve seen them!

What’s the process for getting parts made up? I assume a number of people need them and commit to buy? I’d really not want rock hard poly bush though - I’d rather have original spec rubber.
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g259fsg
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Re: 420GSi tourer engine vibration

Post by g259fsg »

I have the same problem with TV programmes. Happily start watching them and about three minutes in my wife says we've seen this before, I don't want to see it again.

On the serious topic, you could try repairing the engine mountings you've got. I did this on the 214. It has two main mountings, a thing that looks like a snail on the O/S which is relatively cheap and easy to change, and one on the N/S which supports the gearbox which is harder to change and is ridiculously expensive. As originally designed it did a good job of insulating the engine and gearbox noise from the car, but the complicated rubber structure eventually breaks down and sags causing engine/clutch judder. I forked-out once for a new one (nearly £200), but when that went I decided to try a repair - I'd kept the old one so was able to work on it first. I packed it with bits of stiff rubber belt, aluminium and then used silicone rubber sealant to hold it together (I used lead sealant used by roofers which sets very stiff and is incredibly tough). I don't think this is going to break again. The downside is that there is a bit more engine and gearbox noise, but you soon get used to it. You'd probably get the same effect with poly bushes, but they do last a very long time.

Hugh
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