Running in ailments

92 posts / 0 new
Last post
Mucus72
Mucus72's picture
Offline
Last seen: 4 days 21 hours ago
Joined: 17/04/2014

@Lee - I am thinking that I will need to adjust laterally, fabricate some soft wood levers (Jim123 has done this previously, so I'm not a lone nut), loosen gearbox and engine mounts and try and shift it right a little.

THe box does touch the insulation. Much more than touch, it looks like its fully compressing the insulation foam (pressing v hard). The vibrations are high frequency.

@Andrew - yes please Dr.Revill, Caterham consultant... ;) Even better if you had a spare hour (tea and biscuits provided)

revilla
Offline
Last seen: 1 hour 9 min ago
Joined: 17/04/2014

Just back from spending a pleasant couple of hours with Marcus in his garage looking at the vibration issue and promised I would write up what we found. However I have just noticed in the last post above I was promised biscuits with my tea so I'm feeling a little hard done by all of a sudden! Anyway ...

With the engine at idle, there's quite a lot of vibration to be felt throughout the chassis. It is quite noticeable through the seats, body panels and the steering wheel. Much more so than in my car. I should qualify all of this by saying that all of my experience is with K Series so when I compare things with my car I'm not comparing like for l don't know how much of the difference is just K vs. Duratec.

The gearbox is now spaced away from the chassis. There's not a lot of clearance in there but if you press a finger tip in against the points where the gearbox comes close to chassis rails with it running you can feel relative movement between the box and chassis as the engine vibrates, so there is some clearance and I don't think there's much vibration being transmitted through the points where it contacts the heat shielding. It also feels as though the amount of vibration to be felt in the gearbox at that point is a lot less than the vibration you can feel in the chassis, so I don't think gearbox to chassis contact is the primary source of the bodywork vibrations.

The engine mounts feel very firm. When blipping the throttle the whole car can be seen to rock slightly from the torque reaction but it's hard to make out any relative movement of the engine relative to the chassis. However we removed the engine mounting arm to rubber bolts and checked their length and they don't appear to be too long. With these bolts slackened right off the levels of vibration in the bodywork were still about the same, and with the bolts tightened again, using a stethoscope against the central engine mounting rubber bolt and then against the mount to chassis bolts it was clear the mounts were absorbing a lot of the vibrations so appear to be working correctly and are not being clamped out by the central bolt grounding on the bottom plate or anything similar.

There are no other obvious points of contact between the power train and the chassis. The steering column is clear of the exhaust primaries and the exhaust primaries are well clear of the bodywork through the exit hole. There is some light contact between the bell housing and the heat shielding towards the front of the tunnel but I don't think there is firm pressure transmitting engine vibration to the bodywork.

The one thing that really did strike me was just how much vibration is actually being produced by the engine. Certainly comparing it to a K Series, if you put your hand on top of the engine when it is running there is a lot more buzzing vibration. The engine feels very harsh and has actually vibrated the cam cover bolts out as mentioned by Marcus earlier. In addition, if you slowly open the throttle, somewhere around about 2500-3000rpm there is a resonant knocking rattle sound. It is not coming from external engine covers as we tried putting out hands on all the external bits that could be rattling without any effect. It does sound as though it is coming from inside the engine. It's a heavier more mechanical sound that you would get from something external resonating, but it is only really obvious over a narrow RPM band. Using an engine stethoscope the sound appeared to be coming from around the rear end of the inlet camshaft but it wasn't anything like normal cam or lifter noise. It's also not coming from the injectors. It's the kind of noise you might expect if the cam was loose in its bearings; I'm not trying to suggest that it, just to describe the noise a little better.

As I said earlier I have no idea to what extent a Duratec would normally feel harsher than a K series and whether the noises we were hearing were common to Duratec engines but the vibration levels from the engine were such that if it were a K Series I would be concerned that it was distinctly unhealthy. I honestly think that the main reason that there is a lot of engine vibration being transmitted to the chassis is simply because there is a lot of engine vibration.

It almost feels as though there is a problem with engine balancing.

Marcus, as we discussed earlier I think the best course of action now would be to take the car back to the dealer for them to investigate under warranty. In the meantime I would try to familiarise yourself with other 420s and Duratecs in general to try to get a feel for how much of a difference there is between the level of vibrations in your car and others of a similar specification. Tese things are so subjective and difficult to describe that I think the only way you will know if your car is different to others is through direct personal experience of a number of cars for comparison.

SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm

7 wonders of th...
Offline
Last seen: 14 hours 13 min ago
Joined: 17/04/2014

My K and Duratecs were both very smooth, though I do balance mine to a fine tolerance,

Has the mapping been checked?, as this could be inducing vibrations,

revilla
Offline
Last seen: 1 hour 9 min ago
Joined: 17/04/2014

One thing was puzzling me after I left last night Marcus - the frequency of the vibration you are getting. Even at idle, it's quite a high frequency buzzing. If the idle speed of the engine is around 900rpm that's around 15 crank revolutions per second. Just from the feel of it I would say the vibration is higher frequency than 15hz even at idle. I may be wrong and it may be at crank frequency but it's certainly not at cam frequency.

The only way I can see of getting a strong higher frequency vibration from the engine are:

  1. Something that happens multiple times per revolution.
  2. Something that is turning faster than the crank.

If it was vibrating at the frequency of one per firing stroke that would be around 30hz at idle, so that's a possibility but then makes it less likely to be balance related.

The only obvious things that rotate significantly faster than the crank are the pumps and alternator that are belt driven at the front of the engine. I'm not sure how the belts are arranged on a Duratec - does the alternator belt drive other things too? Just wondering if it is possible to remove the alternator belt without losing dry sump pumps and the like just to rule out it being a real problem with balance or bearings in the alternator? Even if not, can you slip the belt off and spin the alternator by hand to see if it feels normal? Any roughness or play in the bearings would be worry, as would any tendency to rotate back to the same position each time you let go. Possibly a very long shot, but thought worth mentioning.

SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm

Mucus72
Mucus72's picture
Offline
Last seen: 4 days 21 hours ago
Joined: 17/04/2014

It's one belt that drives all, but v easy to slacken the tensioner and slip the belt off to hand crank the alternator to check for what you are thinking here. I'm working from home today and will do that at lunch time and report back Andrew. Thanks!

Mucus72
Mucus72's picture
Offline
Last seen: 4 days 21 hours ago
Joined: 17/04/2014

@seven wonders - I have heard of other cars with comments on blatchat where the wrong map was used and Caterham needed to re-flash the ECU. But these were cases of really rough running, and mine doesn't. It is just really severe vibration all of the time. Is this what you mean by mapping or do you mean a map sensor issue. Apologies but I'm not very savvy with this kind of thing...

Steve_K
Steve_K's picture
Offline
Last seen: 1 hour 43 min ago
Joined: 26/01/2015

This may be a red herring but doesn't the Duratec use internal balance shafts to counteract the 4 cylinder engine's intrinsic secondary out of balance forces? The shafts run at double crankshaft speed which might explain the highish frequency observed. Maybe the engine was supplied with the timing for the shafts out of kilter?

Steve

"And we moved! We flashed past the mysterious white signs in the night somewhere..."

revilla
Offline
Last seen: 1 hour 9 min ago
Joined: 17/04/2014

That was precisely something I was talking to Marcus about last night. The problem was, neither of us knew if the Duratec used balancer shafts or not. If it does, I would think you might just be onto something.

SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm

Steve_K
Steve_K's picture
Offline
Last seen: 1 hour 43 min ago
Joined: 26/01/2015

I've just done some checking on Google. While the 2.3 Duratec seems to have balancers, it looks like the 2.0 doesn't although I didn't find anything definitive, just an absence of info. Sorry.

Steve

"And we moved! We flashed past the mysterious white signs in the night somewhere..."

Mucus72
Mucus72's picture
Offline
Last seen: 4 days 21 hours ago
Joined: 17/04/2014

I googled last night and its rather difficult to work out which engines are actually the Duratec ones in our cars. Does anyone else know definitively whether ours have balancer shafts please?