Strange top end rattle?
Discussion
TVR Beaver said:
''500's don't have a shorter skirt?''... Another expert up in smoke 
... I knew they had some work done to them for clearance but was not sure what... so it's just a bit of fettling is it...
Who is the expert that told you that?... I knew they had some work done to them for clearance but was not sure what... so it's just a bit of fettling is it... Edited by TVR Beaver on Sunday 7th August 10:36
v8 racing said:
Who is the expert that told you that?
Twas a guy in the pub who did some work for TVR at one point... not sure he worked on the Serp 500 but he obviously thought he knew his stuff 
So if its pin to piston Rob... I'm assuming when you inspect them they look okay.. it just expands and get noisey at temperature? Why would this interface start to wear in the first place... Isn't the movement done on the small end to pin?
chris52 said:
could this be some kind of detonation/pinking happening in the cyliders that is giving this noise?
Chris
I thought about pinking, and mine started after new head gasket and a skim, so that ties in, but....Chris
I have tried advancing and retarding the ignition (not as a fix, but as an experiment) and it made no difference. Although I did keep it within a couple of degrees of where it supposed to be.
(I also tried disconnecting the vacuum tube)
It really really sounds like tappet rattle
TVR Beaver said:
Twas a guy in the pub who did some work for TVR at one point... not sure he worked on the Serp 500 but he obviously thought he knew his stuff
So if its pin to piston Rob... I'm assuming when you inspect them they look okay.. it just expands and get noisey at temperature? Why would this interface start to wear in the first place... Isn't the movement done on the small end to pin?
The guy in the pub this time is correct!, i thought you had read it from me from another post, they have a much shorter skirt than the stock 4.2 piston, if i get chance later i will do a picy for you.So if its pin to piston Rob... I'm assuming when you inspect them they look okay.. it just expands and get noisey at temperature? Why would this interface start to wear in the first place... Isn't the movement done on the small end to pin?
The pin is a press fit onto the rod so if that is loose you really are in deep poo!, the piston then rolls on pin, the same way as the rocker arm rolls on the shafts and if you ever strip the shafts down it is always the metal shaft that wears before the alloy rocker.
To be honest i am not saying it is 100% it is the pistons in all cases, however the ones i have had here that i have cured has allways turned out to be the pistons/pins that are causing this issue, in quite a number of cases i have changed cams for customers that are under the impression it is the cam causing this problem, although warning them it isn't, obviously down to cost not everyone can afford a strip down and new pistons, so they decide to change the cam anyway, and in every case the end result is it still rattles.
Is Piston slap being suggested as the source of the noise ?
I thought you only usually got this when the engine was cold.
Regarding the idea of clearance between pin and piston, I can understand that on over run the piston is being pulled down by crank inertia instead of being pushed by combustion, but this happens on every exhaust stroke anyway, so it should be there all the while, shouldnt it ?
PS Written before V8racing's last post
I thought you only usually got this when the engine was cold.
Regarding the idea of clearance between pin and piston, I can understand that on over run the piston is being pulled down by crank inertia instead of being pushed by combustion, but this happens on every exhaust stroke anyway, so it should be there all the while, shouldnt it ?
PS Written before V8racing's last post
Edited by WokingWedger on Tuesday 9th August 09:13
I wonder if someone could get a good recording of the sound (I'm stuck in China now for 2 weeks).. see if we are all actualy talking about the same thing... and also see if this is the sound Rob has experianced in the past....
As I've said before, it sounds like two hard metals making the noise to me... not a alloy piston??
As I've said before, it sounds like two hard metals making the noise to me... not a alloy piston??
chris52 said:
As John has already mentioned mine does not make this noise, but this is an interesting thread so I will try throw some sugestions into the pot.
From what I have heard on Johns car this noise only apears on over-run. I would have thought that if there is any play in the small end or anywhere else you would here it at other times especially under load not just over-run.
So what is different on over-run? the only thing I can think of is that the throttle is closed causing a larger vacuum in the plenum chamber and less air(lower compression) in the cylinders. So the vacuum advance on the dissy is at full pelt due to the large vacuum in the plenum also the car will be fuelling to allow Idle there will be some air in the plenum aswell, could this be some kind of detonation/pinking happening in the cyliders that is giving this noise?
Chris
Chris makes a good point here about the vac advance working at this point... I've always thought mine was front of engine and could posably be the advance weights rattling around... I suppose if the vac advance is moveing it, this too could add to the reason behind the noise?.. Worth trying it without the vac pipe attached see if that has any affect?..From what I have heard on Johns car this noise only apears on over-run. I would have thought that if there is any play in the small end or anywhere else you would here it at other times especially under load not just over-run.
So what is different on over-run? the only thing I can think of is that the throttle is closed causing a larger vacuum in the plenum chamber and less air(lower compression) in the cylinders. So the vacuum advance on the dissy is at full pelt due to the large vacuum in the plenum also the car will be fuelling to allow Idle there will be some air in the plenum aswell, could this be some kind of detonation/pinking happening in the cyliders that is giving this noise?
Chris
carsy said:
I cant see the vac advance having anything to do with it. I presume when the revs are dropping your foot is off the throttle and butterfly is closed. When closed distributor wont see any vacuum as the ever so slight vacuum hole is the wrong side of the butterfly to see vacuum.
indeed... lack of sleep etc This may not be the same problem but my 500 had the same noise and i traced it down to cam walk. The cam seems to be pushed against the retainer plate as the revs rise and then rattle against the plate at about 2200 rpm as the revs drop.
If you look on the inside of the front cover you may even find witness marks. Mine started after fitting a stealth cam which i changed 3 times until i found the cause. I recon this only happens on serp engines as they have a cam retainer plate. I made a spacer to take up the 5mm of end float and the noise went. this is not a fault of robs cams but just the design of the engine. I also tried 3 makes of lifters and new rockers, adjustable push rods, oh and 6 front cover gaskets. Would i bother again NO!! just live with it as a characteristic of the 500.
Mark
If you look on the inside of the front cover you may even find witness marks. Mine started after fitting a stealth cam which i changed 3 times until i found the cause. I recon this only happens on serp engines as they have a cam retainer plate. I made a spacer to take up the 5mm of end float and the noise went. this is not a fault of robs cams but just the design of the engine. I also tried 3 makes of lifters and new rockers, adjustable push rods, oh and 6 front cover gaskets. Would i bother again NO!! just live with it as a characteristic of the 500.
Mark
Surely cam walk is an effect of the problems with the follower - cam contact? The spinning of the followers on the cam lobe has 2 purposes AIUI, to maintain the follower wear / oiling at contact and in the bore as well as the secondary action to lever the cam backwards in the engine. I think this line of research is fairly well documented albeit embedded in articles on lairy cam + valve train design parameters, just remember there are 15 other followers all acting on the cam rather than just the one considered ~ but they give you the idea how the varying loads across the cam lobes can be affected.
The oil dispersal from the front cam bearing may actually also help keep the cam front face floating off the retainer IIRC, so dropping oil pressure at that point might be a cause I suppose? (bit esoteric maybe)
TVR serps are a bit hit & miss with retaining plates, they should all have them but the early TVR serps seem to miss them. The 3.9 basis has a full circular retaining plate, unlike the P38 series horseshoe style retainer - but the cam noses are quite different to suit the completely different front cover designs & lack of dizzy...
The oil dispersal from the front cam bearing may actually also help keep the cam front face floating off the retainer IIRC, so dropping oil pressure at that point might be a cause I suppose? (bit esoteric maybe)
TVR serps are a bit hit & miss with retaining plates, they should all have them but the early TVR serps seem to miss them. The 3.9 basis has a full circular retaining plate, unlike the P38 series horseshoe style retainer - but the cam noses are quite different to suit the completely different front cover designs & lack of dizzy...
Cam walk?.. as suggested before.... I don't think mine has a plate anyway?..... noticed the other day on mine that if you hold it exactly at 1200 rpm, it does it a bit at constant rev's??.. May be it is piston related.. but the crank is off-set another few mm over 4.6 cranks.. so what increase in angular rotation does that give on the piston pin?.. very small I would have thought.. so why typicaly is it only 500's... shorter piston skirt giving a bit more piston slap?...
I'll try get a recording of mine over the next few days and post on U-tube....
Anyone any more thoughts / updates / comments on this at all?..
I'll try get a recording of mine over the next few days and post on U-tube....
Anyone any more thoughts / updates / comments on this at all?..
The mention of cam walk and piston slap....it's gone a bit above me to be honest...
Mine was doing it from cold when I tried it last night. Somewhere about 1200rpm just before the revs drop you have the rattle (metallic style) noise, then the noise goes as it drops back to idle 900-1000rpm. I will attempt to record the sound too.
I am finally around over the next few weeks, so I am taking mine into the garage on Monday to see what they can diagnose. Difficult to comment without hearing it in person. So I will see what they come up with too, and come back on the thread.
Mine was doing it from cold when I tried it last night. Somewhere about 1200rpm just before the revs drop you have the rattle (metallic style) noise, then the noise goes as it drops back to idle 900-1000rpm. I will attempt to record the sound too.
I am finally around over the next few weeks, so I am taking mine into the garage on Monday to see what they can diagnose. Difficult to comment without hearing it in person. So I will see what they come up with too, and come back on the thread.
TVR Beaver said:
..the crank is off-set another few mm over 4.6 cranks.. so what increase in angular rotation does that give on the piston pin?
Not comparable IMHO, the pistons & rods are completely different, and the TVR 500s shortened the rods significantly to fit 4.2 pistons (just CD changed from 3.9's basically) so you do have very high rod angularity. The skirt is not substantially reduced ~ like the rumours I've heard of 500's having slipper style pistons? Basically the short rod has a far greater effect than the piston design IYSWIM. TVR made some fast/hard decisions over what components to use & I guess the choice of getting short rods made up was dictated by not purely engineering factors, there are some big Fords with even shorter rods though.. Personally I'd use longer rods and have custom pistons made with the pin as high as reasonably possible if I was doing it myself? IIRC the 4.2's were likely the first RV8 pistons with offset pins as well, carried on into the 4.0/4.6.So if we did assume it was small end related.. where does the noise come from... I don't think that kind of noise could come from pin to bore slap (unless it was like a pr*ck in a buckett type fit).. people have inspected the small ends and reported them to be okay and tight.. re-fit them and the noise is still there.. .Okay, as the piston get's hot the hole will open up more than the steel pin expands so will increase the clearance... but I'm told when cold and inspected they are quite tight?.. you must have some clearance fit here or they would bind up.. so how much tighter than a good push fit can they be when new?...
Or are we talking about the noise coming from side float?.. the con-rod hitting the inside of the piston.. or the pin hitting the piston retaining clips?.. if its side movement then I don't see its much of an issue???
Or are we talking about the noise coming from side float?.. the con-rod hitting the inside of the piston.. or the pin hitting the piston retaining clips?.. if its side movement then I don't see its much of an issue???
Edited by TVR Beaver on Friday 2nd September 21:18
Moycie said:
The mention of cam walk and piston slap....it's gone a bit above me to be honest...
Glad I am not the only one! 
I personally think it might due to crank crawling or follower tiptoeing
I clearly have nothing worthwhile to contribute to the thread so good luck gents... hope you get it sorted. I will be following with interest.
Hello, my name is Bob and I have a top end rattle....
Which I only noticed after changing the pulley bearing on the V belt, this had been whiney for a while so may have hidden other noises.
I first noticed it on the ferry to Le Mans this year, going up the slopes inside the boat is tunnel like and I could hear a rattle just as the revs died to tickover. It worried me for the weekend but did not miss a beat.
I do some work with John C, Ex David Geralds, these days and let him hear it the other day.
Straight away he said cam chain.
In answer to my following questions, he replied as below.
Many do it.
He has changed rattly ones before and they still can rattle after.
They are non adjustable.
He has never known one break.
HTH.
Which I only noticed after changing the pulley bearing on the V belt, this had been whiney for a while so may have hidden other noises.
I first noticed it on the ferry to Le Mans this year, going up the slopes inside the boat is tunnel like and I could hear a rattle just as the revs died to tickover. It worried me for the weekend but did not miss a beat.
I do some work with John C, Ex David Geralds, these days and let him hear it the other day.
Straight away he said cam chain.
In answer to my following questions, he replied as below.
Many do it.
He has changed rattly ones before and they still can rattle after.
They are non adjustable.
He has never known one break.
HTH.
5.0ltr said:
He has changed rattly ones before and they still can rattle after.
Hi Bob... How many miles on your car when it started?? and would you not think putting a new one on would solve it.. or at least change the noise?... chain has been suggested before.. not saying its wrong.. but don't think anyone has solved the problem by changing the chain or even cam?...One thing is for sure... about 75% of the 500's and some 4.6 do it!!!
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