Valve Guide Loose in Head - Options?
Discussion
The only time I have witnessed this kind of bucket damage is on the PUG/Citroen XUD motor the valves recede into the valve seats after huge mileage as expected with no clearance checks/adjust to correct .......The result = zero or close to nowt valve clearance on a cold engine thus the buckets cant rotate 
once the cam lobe digs into the bucket through poor lubrication and no rotation making a trough impression then it definitely wont rotate further adding to the problem 
easily avoided in this case if correct adjustment schedules were adhered to
once the cam lobe digs into the bucket through poor lubrication and no rotation making a trough impression then it definitely wont rotate further adding to the problem easily avoided in this case if correct adjustment schedules were adhered to Edited by Sardonicus on Sunday 11th March 23:00
Sardonicus said:
The result = zero or close to nowt valve clearance on a cold engine thus the buckets cant rotate once the cam lobe digs into the bucket through poor lubrication and no rotation making a trough impression then it definitely wont rotate further adding to the problem easily avoided in this case if correct adjustment schedules were adhered to
On the AJP8 the wear is more likely to occur when the engine is up to temp because the gaps close up as the engine reaches operating temp once the cam lobe digs into the bucket through poor lubrication and no rotation making a trough impression then it definitely wont rotate further adding to the problem easily avoided in this case if correct adjustment schedules were adhered to Initially a cold engine will sound very tappety indeed, once at operating temp there should be very little valve train noise
If a cold engine has little valve train noise it is a good sign of deferred maintenance
Sardonicus said:
The only time I have witnessed this kind of bucket damage is on the PUG/Citroen XUD motor the valves recede into the valve seats after huge mileage as expected with no clearance checks/adjust to correct .......The result = zero or close to nowt valve clearance on a cold engine thus the buckets cant rotate
Except that's not how lifter rotation occurs. You have the mechanism backwards. The lifters rotate when the valves are open not shut. The offset cam lobe creates this when it contacts the lifter. If there is proper valve clearance when the cam lobe is on its base circle then it's not touching the lifter to make it rotate in the first place so clearly rotation doesn't occur when the valves are closed. The presence or absence of a few thou cold clearance doesn't make a scrap of difference to the forces acting when the valves are open.Lifters and cam lobes wear for three main reasons. Lack of lubrication, incorrect material spec or lifters not rotating. Valve clearance is neither here nor there in this equation.
Edited by Mignon on Monday 12th March 09:33
Interesting little snippets of info you provide for the engine. Loose tappets till warm. If anyone gives the engine stick when tappety the valve is closing and opening on the wrong part of the cam lobe so will undergo aggressive acceleration off the seat ( compressive forces) and aggressive negative acceleration on closing (tensile forces). You paint a good picture of the engine and its inherent problems; lightweight block and heads ( less rigidity and strength), high revving ( premature wear compared to moderate revving engines) large change in valve clearances cold to hot which could cause valve and seat damage.
I also wonder if your pics show the insert has moved by cocking over slightly, possible tell tale of ally on right of seat insert and what looks like poor inlet valve seating ( hard to tell from pics) this would put side load on the valve guide and could, in the right circumstances, cause the guide hole wear.
Peter
I also wonder if your pics show the insert has moved by cocking over slightly, possible tell tale of ally on right of seat insert and what looks like poor inlet valve seating ( hard to tell from pics) this would put side load on the valve guide and could, in the right circumstances, cause the guide hole wear.
Peter
Mignon said:
Sardonicus said:
The only time I have witnessed this kind of bucket damage is on the PUG/Citroen XUD motor the valves recede into the valve seats after huge mileage as expected with no clearance checks/adjust to correct .......The result = zero or close to nowt valve clearance on a cold engine thus the buckets cant rotate
Except that's not how lifter rotation occurs. You have the mechanism backwards. The lifters rotate when the valves are open not shut. The offset cam lobe creates this when it contacts the lifter. If there is proper valve clearance when the cam lobe is on its base circle then it's not touching the lifter to make it rotate in the first place so clearly rotation doesn't occur when the valves are closed. The presence or absence of a few though cold clearance doesn't make a scrap of difference to the forces acting when the valves are open.Lifters and cam lobes wear for three main reasons. Lack of lubrication, incorrect material spec or lifters not rotating. Valve clearance is neither here nor there in this equation.
but surely once the trough/gouge starts appearing the bucket cant/wont rotate during the cam lobes duration anyway this was my point ? out of interest on the engine I mention the valve clearances open with temp not the opposite Sardonicus said:
stevieturbo said:
Just stick an LS in it...lol
An engine with hard to source spares like the AJP would make me nervous cyl heads for example or knowing you have very little options for spare parts that can be priced according to availability and not in a good way either 
Used engines are available for about £3.5k
It's almost a drop in replacement, you can use the same ECU, probably get away with minor loom adaptation, but there would be a couple of engine/gbox chassis mount changes (the engine is much longer), and shorter propshaft
Actual cost of an LS conversion would be at least 4x or 5x as much
Failing that with a lot more fabrication you could just pretend it's Chimaera rather than a Cerbera and put in an RV8, there is at least one example in existence
I'm not claiming I'd keep it without the AJP8 though
A couple more observations. It was interesting looking at the link provided to RND who bought the blueprints to the AJP6 engine so they could recreate the original design for some of the parts which fail. It's clear that TVR paid for an engine design from Al Melling and then went through a cost cutting exercise and undid a lot of his good work. It would not surprise me if they also skimped on the materials or design spec of the AJP8 such as for example the quality of the aluminium in the head castings or the valve seat inserts or the valves themselves.
Judging anything from photos is not ideal but it's clear that the inlet seat insert is not sealing all the way round and it does look like there is some evidence the insert has recessed into the port a bit.
When you get this work done I hope the guy retains any measurements taken so you can share them. I'd like to know how big the i/d of the guide bore is now compared to std and also the o/d of the guide itself so we can see which parts wore and by how much. As for fixing this the guide bore needs resizing with a machine reamer to whatever size first cleans the inside of the bore up fully and then a new guide turning out of suitable bronze. For that I would not ideally recommend the manganese bronze (spec number CZ114) which is commonly used for aftermarket valve guides. It's cheap for a bronze which is why people use it as have I in the past but it does not have very long lasting wear characteristics compared to the best bronzes. Colsibro is a good choice.
Judging anything from photos is not ideal but it's clear that the inlet seat insert is not sealing all the way round and it does look like there is some evidence the insert has recessed into the port a bit.
When you get this work done I hope the guy retains any measurements taken so you can share them. I'd like to know how big the i/d of the guide bore is now compared to std and also the o/d of the guide itself so we can see which parts wore and by how much. As for fixing this the guide bore needs resizing with a machine reamer to whatever size first cleans the inside of the bore up fully and then a new guide turning out of suitable bronze. For that I would not ideally recommend the manganese bronze (spec number CZ114) which is commonly used for aftermarket valve guides. It's cheap for a bronze which is why people use it as have I in the past but it does not have very long lasting wear characteristics compared to the best bronzes. Colsibro is a good choice.
The failed guide / head is in my opinion an outlier
That cylinder was horribly compromised by a faulty injector and an oblivious owner
The damage I did by continuing to drive it on track - redlining routinely, cannot be blamed on the design or the manufacturer
If there were similar damage in other cylinders you would have a valid point
I will certainly document the head with as many photos as I can take, but measuring anything awkward is likely to be outside my skillset
That cylinder was horribly compromised by a faulty injector and an oblivious owner
The damage I did by continuing to drive it on track - redlining routinely, cannot be blamed on the design or the manufacturer
If there were similar damage in other cylinders you would have a valid point
I will certainly document the head with as many photos as I can take, but measuring anything awkward is likely to be outside my skillset
I agree with you Dave.
We use a manganese silicon bronze material which is made especially for us. The specs of the material are;
CEN CW713R /British CZ135 /USA SAE CA67410/Germany CuZn40A12 2.0550. This material is specifically suited to valve guides.This is not the common, off-the-shelf CZ114 which is NOT suited to valve guides.
To be honest the heads need a close look over to see if any other problems are surfacing. Again, no one is attacking TVR, you ask for thread input but seem to feel folk are trying to trash the engine. The problem you show on one cylinder is what we have been discussing. It is unusual to see it on a 'young' cylinder head that has not been heavily modified to bring on the onset. Side load has to be generated somewhere for the hole to change shape. I think all the guides need a sharp tap to see if they are 'safe' and the problem manifesting itself on the one guide you mention may not be isolated.
On the other thread you started re loose head nuts, is there any marking to the head where the head nuts/washers sit? If yes it does point to a change in the condition of the head material possibly brought on by heat. We have seen this many times in aftermarket ally heads.
Peter
We use a manganese silicon bronze material which is made especially for us. The specs of the material are;
CEN CW713R /British CZ135 /USA SAE CA67410/Germany CuZn40A12 2.0550. This material is specifically suited to valve guides.This is not the common, off-the-shelf CZ114 which is NOT suited to valve guides.
To be honest the heads need a close look over to see if any other problems are surfacing. Again, no one is attacking TVR, you ask for thread input but seem to feel folk are trying to trash the engine. The problem you show on one cylinder is what we have been discussing. It is unusual to see it on a 'young' cylinder head that has not been heavily modified to bring on the onset. Side load has to be generated somewhere for the hole to change shape. I think all the guides need a sharp tap to see if they are 'safe' and the problem manifesting itself on the one guide you mention may not be isolated.
On the other thread you started re loose head nuts, is there any marking to the head where the head nuts/washers sit? If yes it does point to a change in the condition of the head material possibly brought on by heat. We have seen this many times in aftermarket ally heads.
Peter
ukkid35 said:
The failed guide / head is in my opinion an outlier
That cylinder was horribly compromised by a faulty injector and an oblivious owner
The damage I did by continuing to drive it on track - redlining routinely, cannot be blamed on the design or the manufacturer
If there were similar damage in other cylinders you would have a valid point
My point, which is valid, is that mild detonation is a very common occurence but valve guide bores ending up 1mm bigger than the guide are not. I'm a scientist. I'm interested in the causes here rather than just the symptoms. Spending a lot of money fixing what you see as the obvious fault will not help if other things are only going to break later. It may be that is not a lot of material around the guide bores which makes them structurally weaker than in most heads. It may be the grade of aluminium or the heat treatment involved is not ideal. Even if I can see a reason for the guide becoming loose because the head overheated I'm still struggling to see why the bore got so big. High silicon aluminium is a very good bearing material against certain other materials. For instance the lifter buckets run directly in the head as do the camshafts but they don't wear the bores out. Bronze is a reasonably good material to run against aluminium so even if the guide was moving up and down with the valve I'm surprised it would wear the bore out like this. If the guide bore has worn by what looks like almost 1mm and that's mainly on one side it would need reaming out by 2mm to clean up. That's a non trivial amount in terms of the strength of the surrounding material.That cylinder was horribly compromised by a faulty injector and an oblivious owner
The damage I did by continuing to drive it on track - redlining routinely, cannot be blamed on the design or the manufacturer
If there were similar damage in other cylinders you would have a valid point
I note the valve guides are stepped which is unusual. This prevents them fallling into the chamber if they come loose but maybe there is a reason this was felt necessary. If the strut of material in which the guide bore hole is machined is not very robust then reaming it to a larger size will make it weaker still. Then pressing the new guide in will just expand the aluminium strut rather than creating a tight fit.
I have noted that the valve seat insert looks as though it might be recessing and you have said that head nuts have come loose. The aluminium hardness might be a factor in both of these as well as the guide coming loose. It's not difficult to tell how hard and well heat treated aluminium is by how it machines. A light flycut across the head face without lubricant would indicate if it machines cleanly or if it tears because it's now soft. An experienced engineer could tell a lot from this. The Rover K series engine cylinder heads are well known for becoming soft and no longer taking a head gasket properly.
If I were in your shoes I would want to speak to Al Melling who designed the engine. I imagine he might be interested in such an unusual case. As Peter Burgess has said he would also be interested to take a look and you might benefit from this before you decide on what work to have done. I'm also happy to consult from whatever feedback comes our way. FOC obviously. Between us Peter and myself have over 60 years experience of this sort of thing. That's a resource you could be well advised to take advantage of when so much money and potential future reliability is at stake.
Thank you both once again for continuing to contribute your time and experience - it is very much appreciated
Sorry if I appear to have been overly defensive of TVR's engine, but they get so much criticism that I really wanted to point out that my negligence is largely responsible for the damage
Here is more evidence from about a year or 4000 miles ago that I chose to ignore
The right hand plug is from the damaged cylinder
Sorry if I appear to have been overly defensive of TVR's engine, but they get so much criticism that I really wanted to point out that my negligence is largely responsible for the damage
Here is more evidence from about a year or 4000 miles ago that I chose to ignore
The right hand plug is from the damaged cylinder
OIl coming down the outside of the valve guide will have fouled that plug. Also oil contamination reduces the fuel octane value which may have contributed to detonation. It does rather beg the question which came first though, the chicken or the egg? Did the guide come loose and cause det or did det cause the guide to come loose. Maybe that guide was loose from the factory.
stevieturbo said:
Maybe it's more common with ( semi ) modern stuff ?
LS engine valve guides have a collar on them so they install to correct height easily. You can buy guides for Subarus that are like that too
Sierra Cosworth guides had a circlip on them to set the height if I recall correctly but otherwise it's very rare. It's obviously more expensive to make a guide like that and uses more material. It also prevents you from easily fitting the guide lower to suit high lift cams. A quick google for "shouldered valve guides" shows mainly aftermarket items from the USA. According to google the stock LS guides I can see on various websites are not shouldered but it's not an engine I've ever worked on.LS engine valve guides have a collar on them so they install to correct height easily. You can buy guides for Subarus that are like that too
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