Another day another cam
Discussion
A worn can will just reduce the valve lift and shouldn't affect a compression test, this will be either valves or piston rings letting by an giving the low readings. Try again with a bit of oil in the bores and see is it changes much. If it's the rings then the oil will allow a higher reading, if it's the valves letting by it will stay similar.
Don't forget you should be doing your compression test with the throttle wedged open and a compression test will not be an indicator of a worn cam.
If you fancy buying more tools a leakdown tester can be useful.
You take the cylinder to be tested to TDC firing stroke and fit the tester in place of the spark plug and connect it to an airline.
If something is leaking you can listen at various places for the hissing sound.
Listen for hiss at:-
Exhaust pipe = duff exhaust valve
Oil filler = duff rings
Pipe into plenum = duff inlet valve
Bubbles in coolant = head gasket etc.
Steve
If you fancy buying more tools a leakdown tester can be useful.
You take the cylinder to be tested to TDC firing stroke and fit the tester in place of the spark plug and connect it to an airline.
If something is leaking you can listen at various places for the hissing sound.
Listen for hiss at:-
Exhaust pipe = duff exhaust valve
Oil filler = duff rings
Pipe into plenum = duff inlet valve
Bubbles in coolant = head gasket etc.
Steve
canonc said:
And what would be the best one for my Chimaera 450?
That all depends on what you want it to do. If you were happy with the way it behaved before, and the cam is a TVR 435 (should be stamped on the end of the cam along with a load of other numbers), then go for the modern equivalent which is the TVR 885. You can get one from a number of places: Kent cams distributor, Powers Performance, V8 Tuner, etc.If you want something different, then well, that is a can of worms I opened a while back and it took some time to whittle it down
For me there are two camps/trains of thought. One that wants max bhp figures and pub bragging rights. The other that wants the car to 'feel' fast and is not bothered what the dyno says, but will still get a dyno done because they're curious what it's making
All IMO of course.
Just my tuppence worth.
Thank you Steve D for the info. As for the piston rings, if there is a leak down, would there also be a leak up and oil on the plugs? All the plugs are dry and clean.
I became aware that I may have a problem, driving from a garage who had just completed a 12000 mile service. On the way home it started to miss and shunt, something it didn't do before! Shortly after there was a fairly loud tapping noise. But I will take onboard all of your checks. And many thanks.
And thank you also to Caduceus for pointing me in the direction of a Cam, if needed it is needed.
I became aware that I may have a problem, driving from a garage who had just completed a 12000 mile service. On the way home it started to miss and shunt, something it didn't do before! Shortly after there was a fairly loud tapping noise. But I will take onboard all of your checks. And many thanks.
And thank you also to Caduceus for pointing me in the direction of a Cam, if needed it is needed.
canonc said:
Thank you Steve D for the info. As for the piston rings, if there is a leak down, would there also be a leak up and oil on the plugs? All the plugs are dry and clean...........
A piston has compression rings and oil control ring(s).The compression rings could be letting compression escape but that does not mean the oil ring is not doing its job.
Steve
It seems odd that the problem just started after a 12,000 mile service. 
As all the cylinders except number 4 are about the same, I would ignore them and concentrate on 4.
The misfiring and the tapping sound "Shortly after there was a fairly loud tapping noise" indicate possibly that a hydraulic lifter (tappet) may have become stuck in the closed position.
Hydraulic tappets can begin to close down as the oil in them slowly oozes out especially if the oil is drained and a long time passes before refilling with new oil and running the engine. On start up one or more may not instantly fill with oil so will not open the valve properly.
I have cleared this in the past by getting the engine hot, revving to 4,000 rpm for a minute then letting it idle. Switch off and repeat. If it is a lifter blocked or stuck you can try an additive. If it is really blocked and you don't want to strip the engine you could try an engine flush and a treatment.
https://www.google.co.uk/webhp?sourceid=chrome-ins...
As all the cylinders except number 4 are about the same, I would ignore them and concentrate on 4.
The misfiring and the tapping sound "Shortly after there was a fairly loud tapping noise" indicate possibly that a hydraulic lifter (tappet) may have become stuck in the closed position.
Hydraulic tappets can begin to close down as the oil in them slowly oozes out especially if the oil is drained and a long time passes before refilling with new oil and running the engine. On start up one or more may not instantly fill with oil so will not open the valve properly.
I have cleared this in the past by getting the engine hot, revving to 4,000 rpm for a minute then letting it idle. Switch off and repeat. If it is a lifter blocked or stuck you can try an additive. If it is really blocked and you don't want to strip the engine you could try an engine flush and a treatment.
https://www.google.co.uk/webhp?sourceid=chrome-ins...
Thank you for the input. N7GTX. Will bare your information in mind.
Yes I was expecting great things from the service by a well know Tvr garage in Cirencester. Didn't expect the engine to behave the way it did. No blame attached to the garage!
My original thought was a lifter or tappet face problem.
I use Penrite oil and wouldn't think they would replace like for like oil, and when I trace the problems I will change back to Penrite Oil. Thanks CassiChimi
Perhaps I am going down the wrong road in my thinking, that the miss-fire and tapping noise are born out of the same problem, when in fact they are different! The service included new plugs and I have just fitted a new dist.cap and rotor arm.
Cy
Yes I was expecting great things from the service by a well know Tvr garage in Cirencester. Didn't expect the engine to behave the way it did. No blame attached to the garage!
My original thought was a lifter or tappet face problem.
I use Penrite oil and wouldn't think they would replace like for like oil, and when I trace the problems I will change back to Penrite Oil. Thanks CassiChimi
Perhaps I am going down the wrong road in my thinking, that the miss-fire and tapping noise are born out of the same problem, when in fact they are different! The service included new plugs and I have just fitted a new dist.cap and rotor arm.
Cy
Ask them point blank what oil they use and persist until they tell you.
Mineral 20w50 bought in 205 litre drums can be less than £1 per litre.
So unless they have specified on the invoice what they used, it may be this sort of stuff.
Not saying it's unsuitable, but it ain't Penrith (the Lake District version of the oil you already use - bloody Ipad!), Shell or Castrol.
So you changed the rotor arm and distributor cap........hmmmm.
Try the old ones again, if you have kept them.
There have been comments about new Lucas components on here, with the words "cheap" "Chinese" and "crap" featuring regularly.
Mineral 20w50 bought in 205 litre drums can be less than £1 per litre.
So unless they have specified on the invoice what they used, it may be this sort of stuff.
Not saying it's unsuitable, but it ain't Penrith (the Lake District version of the oil you already use - bloody Ipad!), Shell or Castrol.
So you changed the rotor arm and distributor cap........hmmmm.
Try the old ones again, if you have kept them.
There have been comments about new Lucas components on here, with the words "cheap" "Chinese" and "crap" featuring regularly.
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