Ticking Griffs
Discussion
Hummm where do you start
Noisy engines ticking around the top end sometimes loud and more than one tick!
TVR took these old engines and the ally heads and fitted bloody great exhaust valves as big as they could fit in really . Unfortunatly force = pressure x area so the exhaust valves slowly work their way into the heads.
If you put a straight edge along the top of the valve stems, first remove the rocker shaft of course you will more than likely find the the exhaust valve stems protrude a lot further than the inlet valve stems.
as setting up the clearences on the valves is at best hit and bloody miss , bits of bent welding rods , even so the only solution is to either remove the heads and recut all the seats or new heads.
expensive
Noisy engines ticking around the top end sometimes loud and more than one tick!
TVR took these old engines and the ally heads and fitted bloody great exhaust valves as big as they could fit in really . Unfortunatly force = pressure x area so the exhaust valves slowly work their way into the heads.
If you put a straight edge along the top of the valve stems, first remove the rocker shaft of course you will more than likely find the the exhaust valve stems protrude a lot further than the inlet valve stems.
as setting up the clearences on the valves is at best hit and bloody miss , bits of bent welding rods , even so the only solution is to either remove the heads and recut all the seats or new heads.
expensive
Regardless of the spring loads (they close the valve)the closing force is drastically increased due to the diameter of the valve , this extra force increases wear on the cam lobes and wears the valve seats.
A common enough symptom of an average milage Griff 500 engine. It is always the exhaust cam lobes that wear the worst.
I am wondering if there is any hardened inserts on the market or does anyone know a good place to get the heads reworked
A common enough symptom of an average milage Griff 500 engine. It is always the exhaust cam lobes that wear the worst.
I am wondering if there is any hardened inserts on the market or does anyone know a good place to get the heads reworked
siwes said:
Regardless of the spring loads (they close the valve)the closing force is drastically increased due to the diameter of the valve , this extra force increases wear on the cam lobes and wears the valve seats.
A common enough symptom of an average milage Griff 500 engine. It is always the exhaust cam lobes that wear the worst.
I am wondering if there is any hardened inserts on the market or does anyone know a good place to get the heads reworked
No sorry, you've still lost me.
Are you talking about the valve seat inserts wearing, or the valve seat inserts being hammered into the heads
, or cam lobe wear? Cam lobe wear is a routine problem with these engines (although tbh I rather doubt that valve size has anything to do with it), valve seat problems are a different kettle of fish entirely and are not common as far as I'm aware. If you're suggesting that the bigger valves require stiffer springs and hence put higher loads on the cam followers, this would imply that the inlet lobes would wear first since the inlet valves are bigger and heavier than the exhaust valves?
Edited to add: but obviously, cam lobe wear would not show up as variations in the valve stem height; that would only be caused by receding valves, and I haven't understood yet why you think bigger valves make this worse or why you think it is a problem that TVRs suffer from.
If the problem is specific to the exhaust valves as you say (Ive no figures to support this theory) then perhaps the fact that the exhaust valve runs a lot hotter than the intake valve has something to do with it?
>> Edited by GreenV8S on Friday 14th October 18:11
siwes said:
Regardless of the spring loads (they close the valve)the closing force is drastically increased due to the diameter of the valve , this extra force increases wear on the cam lobes and wears the valve seats.
A common enough symptom of an average milage Griff 500 engine. It is always the exhaust cam lobes that wear the worst.
I am wondering if there is any hardened inserts on the market or does anyone know a good place to get the heads reworked
How can it be 'regardless of spring loads'?
Larger valves may have a slightly higher mass, requiring a higher spring rate to control them therefore adding to cam wear, but I can't see how a larger valve directly influences the loads on the cam?
If it's pressure related asd you suggest the inlets would move further, they have heads about 20% bigger than the exhaust, the chamber pressure is the same but over the larger area of the inlet head will produce a larger force.
However this force is spread over a larger circumference seat, so that reduces it again.
however the exhaust valve seat is a wider one, so that reduces the exhaust seat loading .. lol.
what figures are you using to come to your decision? Have you compared the inlet and exhaust stem lengths? have you measured the valve seat pressures/preload on the springs?
However this force is spread over a larger circumference seat, so that reduces it again.
however the exhaust valve seat is a wider one, so that reduces the exhaust seat loading .. lol.
what figures are you using to come to your decision? Have you compared the inlet and exhaust stem lengths? have you measured the valve seat pressures/preload on the springs?
yes the valve heights are different the exhaust valve seats are receding into the heads that puts more load on the rocker arms and no clearence on the cam follower hence the wear on the cam lobes .
This is why the engines eat cam shafts and followers not to mention rocker arm pads they disintergrate
This is why the engines eat cam shafts and followers not to mention rocker arm pads they disintergrate
As far as I can see the valve seats would have to recede by more than the amount of adjustment in the lifters before you saw any cam problems, and having worn that badly it would be blatantly obvious when you came to change the cam because you wouldn't be able to get the preload right for the inlet and exhaust at the same time. If this was a common problem then cam changes would routinely be accompanied by head rebuilds. In practice they aren't, which makes me think that this probably isn't a common problem. But it's an interesting theory, and I'm looking forward to seeing Rob's response.
The valve seats on all rv8 engines from around the late 80's are all hardened seats and i have never seen valve seat recesion, yep on the early cars with soft seats it was a problem when used with lead free fuels but now adays, as for the size of the valves??? this would mean chevy motors with valve sizes of over 2 inch and spring pressures of touching 400 ib would need new seats every day? if it is still happening today that you have valve heights of difference lengths it is down to only one thing, poor seat cutting to start with, 99% are well with in tolorence
I think the problem is happening a lot with these engines, whenever I hear an older Griff you can be sure there is usually a ticking around the top end , listen to a range rover even old ones lovely and quiet.
TVR have increased the valve sizes they pour as much fuel and air in as they can get , and the heads really are not up to the job, that is why I think the power output falls off so quickly on these engines .
my heads when I put a straight edge across the valve stems had at the No 1 cylinder inlet valve 60 thou difference in height from the exhaust valve. That was the worst, they were all more than 40 thou difference.
It is impossible to shim the rockershaft pillars to correct for this .
The only repair recut the seats or new heads.
The number of threads I read about new cams, ticking engines , loss of power, lifters badly marked , most of these problems are coming from incorrect clearences on the valves
TVR have increased the valve sizes they pour as much fuel and air in as they can get , and the heads really are not up to the job, that is why I think the power output falls off so quickly on these engines .
my heads when I put a straight edge across the valve stems had at the No 1 cylinder inlet valve 60 thou difference in height from the exhaust valve. That was the worst, they were all more than 40 thou difference.
It is impossible to shim the rockershaft pillars to correct for this .
The only repair recut the seats or new heads.
The number of threads I read about new cams, ticking engines , loss of power, lifters badly marked , most of these problems are coming from incorrect clearences on the valves
I meant to add , what else can be the cause of the problem of worn out cams, dished and cracked followers loss of power sometimes very noisy top ends and in a bad case this happens within a few thousand miles , TVR have upped the compression ratio in the heads from a gentle 8.8:1 to in some cases 11.5:1 the loading on the valve seats has increased over 30% Im sure the seats can take the load unfortunatly the surrounding material that supports the hardened seats cannot.
And the seats are indeed being hammered up into the heads.
And the seats are indeed being hammered up into the heads.
If I've understood you correctly, your theory is that increased valve area and cylinder pressure is increasing the peak load on the valves, the structure around the exhaust valve is not strong enough to take this stress and is yielding allowing the valve seats to recede into the head, this increases the preload on the lifters until they run out of travel, at which point the valve clearances close up and the lifter starts wearing the cam. Is that what you are suggesting?
It's a novel theory, I'll give you that. I have to admit it doesn't sound particularly likely to me. If the valves had receded then this would be obvious to anyone setting the preloads after a cam change. Cam changes are quite routine so for the problem to be common and to have passed unnoticed, fitters across the country would have to be neglecting to reset the preloads and/or spectacularly incompetant. This seems extremely unlikely to me and my conclusion is that valve recession is probably NOT a common problem.
What I suspect is a more common problem is failure to bed new cams in properly, some people I speak to say it isn't necessary but traditional wisdom is that it is critical. If you don't bed the cam in, it may damage the cam/lifter bearing surface reducing the cam life dramatically. The effects would only be apparent much later on as premature cam wear, and there would be no direct evidence that it had been caused by lack of bedding in.
It's a novel theory, I'll give you that. I have to admit it doesn't sound particularly likely to me. If the valves had receded then this would be obvious to anyone setting the preloads after a cam change. Cam changes are quite routine so for the problem to be common and to have passed unnoticed, fitters across the country would have to be neglecting to reset the preloads and/or spectacularly incompetant. This seems extremely unlikely to me and my conclusion is that valve recession is probably NOT a common problem.
What I suspect is a more common problem is failure to bed new cams in properly, some people I speak to say it isn't necessary but traditional wisdom is that it is critical. If you don't bed the cam in, it may damage the cam/lifter bearing surface reducing the cam life dramatically. The effects would only be apparent much later on as premature cam wear, and there would be no direct evidence that it had been caused by lack of bedding in.
This is not an isolated incident, the proof is there in the valves , I have to say the performance of my engine was excellent the only reason the heads were taken off was the noise , I don't know at what excessive lack of clearance the real damage occurs but it was starting
I wasn't out to prove a point , I was just stating what I found , on close inspection of the combustion chamber it is quite obvious that the remaining material to hold the enlarged seats does not look substantial.
asking around this is quite a well know fault with these heads , they were simply never designed to give the sustained power and loads that TVR asked of them.
My only point was to answer the MANY threads on ticking engines that appear on this forum. It is an easy check just the rocker cover off the rocker shaft removed and a steel rule with a set of feeler gauges, be prepared to be horrified
I wasn't out to prove a point , I was just stating what I found , on close inspection of the combustion chamber it is quite obvious that the remaining material to hold the enlarged seats does not look substantial.
asking around this is quite a well know fault with these heads , they were simply never designed to give the sustained power and loads that TVR asked of them.
My only point was to answer the MANY threads on ticking engines that appear on this forum. It is an easy check just the rocker cover off the rocker shaft removed and a steel rule with a set of feeler gauges, be prepared to be horrified
I assume the valve clearances were originally correct and the seats were correctly fitted and lapped in to the valves. Are you using standard TVR heads, or have they been fettled subsequently?
Is it possible to tell from inspection whether the recession in your case was caused by the valve seats wearing, or by them being pushed back into the head? If the valves seats have been pushed into the head by 60 thou or so I would have thought you would find signs of structural failure around the exhaust ports. I assume the heads would be scrap in this case.
Is it possible to tell from inspection whether the recession in your case was caused by the valve seats wearing, or by them being pushed back into the head? If the valves seats have been pushed into the head by 60 thou or so I would have thought you would find signs of structural failure around the exhaust ports. I assume the heads would be scrap in this case.
interesting techie stuff.
i always suspected that the valves were overspung on the std 500. severe cams running high pressures = cam wear. lots of revs can increase this.
my tuscan engine with roller rockers/solids and 256 cam is lovely and quiet over several hundred track miles now. revs to 7.2k rev limit (7.8k max advised)
i always suspected that the valves were overspung on the std 500. severe cams running high pressures = cam wear. lots of revs can increase this.
my tuscan engine with roller rockers/solids and 256 cam is lovely and quiet over several hundred track miles now. revs to 7.2k rev limit (7.8k max advised)
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