Valve Guide Loose in Head - Options?
Discussion
Having removed the valves I have found that one of the valve guides isn't worn as such, but rather it is very loose in the head
Are there oversized valve guides?
What do I need to keep in mind when I take the heads back to my preferred engineer (Roland Alsop as previously recommended by Charlie at SRR - they did a great job a couple of years ago at re-surfacing the heads the last time)?
Are there oversized valve guides?
What do I need to keep in mind when I take the heads back to my preferred engineer (Roland Alsop as previously recommended by Charlie at SRR - they did a great job a couple of years ago at re-surfacing the heads the last time)?
ukkid35 said:
Having removed the valves I have found that one of the valve guides isn't worn as such, but rather it is very loose in the head
Are there oversized valve guides?
What do I need to keep in mind when I take the heads back to my preferred engineer (Roland Alsop as previously recommended by Charlie at SRR - they did a great job a couple of years ago at re-surfacing the heads the last time)?
You need to give the head to Steve and let him fix it while you have a drink and don't worry about it.Are there oversized valve guides?
What do I need to keep in mind when I take the heads back to my preferred engineer (Roland Alsop as previously recommended by Charlie at SRR - they did a great job a couple of years ago at re-surfacing the heads the last time)?
Although why a guide has come loose in the first place...would be of more concern than it actually being loose. IMO take the heads to Steve complete, dont take them apart.
stevieturbo said:
Although why a guide has come loose in the first place...would be of more concern than it actually being loose.
I doubt it's pure chance that it's the same cylinder that there were some serious issues last timeFire ring distortion
Pitting before head skim
Fire ring seal damage
227bhp said:
For what?
That looks like detonation damage btw and i'm very doubtful it had anything to do with a loose guide.
Agreed, but probably either caused by pinking/detonation, or has a common causeThat looks like detonation damage btw and i'm very doubtful it had anything to do with a loose guide.
Oversized guide because there's no way a direct replacement is going to stay in place
ukkid35 said:
227bhp said:
For what?
That looks like detonation damage btw and i'm very doubtful it had anything to do with a loose guide.
Agreed, but probably either caused by pinking/detonation, or has a common causeThat looks like detonation damage btw and i'm very doubtful it had anything to do with a loose guide.
Oversized guide because there's no way a direct replacement is going to stay in place
Since the pitting is no worse than before, I'm going to bet that changing a faulty injector has almost fixed the pinking issue
Getting the cam timing right has helped a lot too, but I'm not claiming the pinking is completely banished
Perhaps the fact that cylinder's intake is the closest to the crank case breather is a significant factor too
Getting the cam timing right has helped a lot too, but I'm not claiming the pinking is completely banished
Perhaps the fact that cylinder's intake is the closest to the crank case breather is a significant factor too
As per above really, give it to someone who knows what they are doing.
TVR will have likely used an existing off-the-shelf guide and a specialist will know what it was and if oversized are available. Otherwise it's a matter of spending some time with a guide catalogue or ultimately having one made, it's certainly not the end of the World.
TVR will have likely used an existing off-the-shelf guide and a specialist will know what it was and if oversized are available. Otherwise it's a matter of spending some time with a guide catalogue or ultimately having one made, it's certainly not the end of the World.
Heads that have detonated and severely overheated as yours did can suffer from distorted and oversized guide bores and consequently loose guides. I recall a big valve CVH turbo head I did many years ago getting detonated badly on the rolling road by a tuner who didn't understand the mapping software properly and the next thing that happened was a guide came loose. With many engines, including the aforementioned CVH, the new guides come a tad large as it is and I routinely used to have to polish them down in the lathe a thou or so before fitting so it may be that just a new guide will do the job. It did in the case I mentioned. A new guide with no polishing down took up the slack perfectly. In extremis it might be necessary to make a special oversized guide from scratch from bronze bar. I've had to do that before too on several occasions. It will be necessary to measure the guide bore accurately with a special bore gauge and compare to nominal specs to see what might need to be done. It's not something I'd trust most ordinary engine reconditioners to be able to do. They're used to banging standard sized things into standard sized holes but not much cop at anything out of the ordinary. They probably won't actually have a clue what the standard interference fit should even be. They'll just expect a new guide to be the right size because someone else has already done the design work. For most engines you want the guide to be about 1.5 to 2 thou larger than the bore it's being pressed into but it depends on whether the head is iron or alloy and whether the guide is iron or bronze. Iron heads don't expand as much as alloy ones so the guide fit doesn't need to be as tight.
Your head is clearly alloy and if the guides are iron I would recommend a 2.2 thou fit and with bronze guides this can drop a tad to 1.9 thou. That's for an average diameter guide in the 13mm region. Adjust proportionately for bigger or smaller guides. I can advise further if necessary. Just for reference with cast iron heads the fit would be 1.5 thou with iron guides and as little as 1.2 thou with bronze ones. Bronze expands more than iron so the guide will actually get tighter as the engine warms up. Aluminium alloy expands more than bronze and lots more than iron so the guides get looser as the engine heats up and the cold fit needs to be tighter. With iron guides in iron heads both components expand at the same rate so the fit stays the same at high temperature. What you should therefore have deduced from the above is that you need 1.5 thou fit (iron guide into iron head) when the engine is hot to keep the guide in place and any change from this when fitting guides at room temperature is to allow for expansion of the different materials.
If the guide bore is now a bit big for a stock guide but not too much so there is still a bit of interference fit but not quite enough then there's a "bodge" if you're experienced enough to know how to do it properly. With the edge of a sharp hand file you whack seven types of bejeezus out of the o/d of the guide all up and down it to knurl up the surface and raise lots of little bumps which increase the interference fit. Then fit it with a good coating of high strength Loctite retainer. You can take up about 1 thou of extra play like this but no more. It's not a technique for the novice or the faint hearted.
Most jobbing engine reconditioners fit guides with a press or by shrinking the guide first with liquid nitrogen. That means they have little real idea of how tight it is or how tight it should be. I used to fit all my guides by hand with a hammer and punch so I knew every time if the feel of the fit was right. An experienced expert will know instantly if a guide is going in too easily and therefore likely to come loose when the engine is up to temperature. I could even tell you exactly how many blows with my favourite 4lb lump hammer each type of guide should take to fit until the punch bottomed out on the fitting collar. When I was training apprentices I used to take a certain amount of pride in demonstrating this as I taught them. I'd polish a guide down in the lathe to the perfect size I wanted and then tell the lad it should take exactly 7 blows for example before the punch bottomed out. Then we'd count each whack and hopefully there'd be 6 dull sounding blows and on the 7th blow we'd hear the sharp clang as the punch hit the steel fitting collar and the guide was down to depth. The same technique would tell me if the fit was right when I was putting in oversized seat inserts for big valve heads.
Your problem should be simple enough to fix for an expert with the right equipment but then most things are easy when you know how. I can't help you in person as I don't do this stuff any more but you might want to consider Peter Burgess who posts in here sometimes. I know he can also make special one-off guides if that needs doing. Otherwise simply give the fits I specify above to whoever you choose and hope they can measure things properly and follow them.
Your head is clearly alloy and if the guides are iron I would recommend a 2.2 thou fit and with bronze guides this can drop a tad to 1.9 thou. That's for an average diameter guide in the 13mm region. Adjust proportionately for bigger or smaller guides. I can advise further if necessary. Just for reference with cast iron heads the fit would be 1.5 thou with iron guides and as little as 1.2 thou with bronze ones. Bronze expands more than iron so the guide will actually get tighter as the engine warms up. Aluminium alloy expands more than bronze and lots more than iron so the guides get looser as the engine heats up and the cold fit needs to be tighter. With iron guides in iron heads both components expand at the same rate so the fit stays the same at high temperature. What you should therefore have deduced from the above is that you need 1.5 thou fit (iron guide into iron head) when the engine is hot to keep the guide in place and any change from this when fitting guides at room temperature is to allow for expansion of the different materials.
If the guide bore is now a bit big for a stock guide but not too much so there is still a bit of interference fit but not quite enough then there's a "bodge" if you're experienced enough to know how to do it properly. With the edge of a sharp hand file you whack seven types of bejeezus out of the o/d of the guide all up and down it to knurl up the surface and raise lots of little bumps which increase the interference fit. Then fit it with a good coating of high strength Loctite retainer. You can take up about 1 thou of extra play like this but no more. It's not a technique for the novice or the faint hearted.
Most jobbing engine reconditioners fit guides with a press or by shrinking the guide first with liquid nitrogen. That means they have little real idea of how tight it is or how tight it should be. I used to fit all my guides by hand with a hammer and punch so I knew every time if the feel of the fit was right. An experienced expert will know instantly if a guide is going in too easily and therefore likely to come loose when the engine is up to temperature. I could even tell you exactly how many blows with my favourite 4lb lump hammer each type of guide should take to fit until the punch bottomed out on the fitting collar. When I was training apprentices I used to take a certain amount of pride in demonstrating this as I taught them. I'd polish a guide down in the lathe to the perfect size I wanted and then tell the lad it should take exactly 7 blows for example before the punch bottomed out. Then we'd count each whack and hopefully there'd be 6 dull sounding blows and on the 7th blow we'd hear the sharp clang as the punch hit the steel fitting collar and the guide was down to depth. The same technique would tell me if the fit was right when I was putting in oversized seat inserts for big valve heads.
Your problem should be simple enough to fix for an expert with the right equipment but then most things are easy when you know how. I can't help you in person as I don't do this stuff any more but you might want to consider Peter Burgess who posts in here sometimes. I know he can also make special one-off guides if that needs doing. Otherwise simply give the fits I specify above to whoever you choose and hope they can measure things properly and follow them.
Mignon said:
Your problem should be simple enough to fix for an expert with the right equipment but then most things are easy when you know how. I can't help you in person as I don't do this stuff any more but you might want to consider Peter Burgess who posts in here sometimes. I know he can also make special one-off guides if that needs doing. Otherwise simply give the fits I specify above to whoever you choose and hope they can measure things properly and follow them.
Many thanks for taking the time to reply in such detail, I really appreciate thatMignon said:
227bhp said:
For what?
That looks like detonation damage btw and i'm very doubtful it had anything to do with a loose guide.
Then you'd be wrong because detonation is a very common cause of this.That looks like detonation damage btw and i'm very doubtful it had anything to do with a loose guide.
I disagree about bashing guides in though, a big no for me. I use a press every time and you get as much feel for that as you do a hammer, you feel it through the pumping handle and see it on the gauge.
They don't need reaming out after and it doesn't knock seven bells out of my hands and arms too.
Each to his own though.
How do you measure the valve stem clearance? I am intrigued as we spend a small fortune on fixed reamers, adjustable reamers and adjustable hones for correct guide clearance. Our Mira system uses pilots which rotate in the guide so we have pilots to suit each application. Our Peg system and SP Nuway system uses expanding pilots so as long as the valve gores in it seems like clearance is adequate. However, we use the Mira pilots as go no go gauges to ensure correct guide ID. Occasionally we find sintered guides which do not need reaming on fitment but very rarely!
I have seen ensuing overheating caused by det damage to pistons and ring lands and rings cause ex valves and inlet valves to seize in guide and then come loose. We have also seen many guides come loose as they have been made with bu**er all interference fit so the guides didn't have to be reamed after fitting! We use both a press to fit guides and a trusty hammer and drift (especially with horribly angled guides in heads), Keith has been doing this for 22 years since he has been with us though!
Peter
I have seen ensuing overheating caused by det damage to pistons and ring lands and rings cause ex valves and inlet valves to seize in guide and then come loose. We have also seen many guides come loose as they have been made with bu**er all interference fit so the guides didn't have to be reamed after fitting! We use both a press to fit guides and a trusty hammer and drift (especially with horribly angled guides in heads), Keith has been doing this for 22 years since he has been with us though!
Peter
227bhp said:
I've never seen det' loosen a guide, but in this instance it seems possible - I was wondering how someone could have put it in so loose. I'd be interested to know exactly how detonation can loosen a guide because I can't imagine how.
Det gets the aluminium temperature up close to melting. The metal becomes soft and pliable. Items like guides and valve seats which are in under a lot of pressure start to deform the soft aluminium and make the holes bigger.Mignon said:
227bhp said:
I've never seen det' loosen a guide, but in this instance it seems possible - I was wondering how someone could have put it in so loose. I'd be interested to know exactly how detonation can loosen a guide because I can't imagine how.
Det gets the aluminium temperature up close to melting. The metal becomes soft and pliable. Items like guides and valve seats which are in under a lot of pressure start to deform the soft aluminium and make the holes bigger.ukkid35 said:
Having removed the valves I have found that one of the valve guides isn't worn as such, but rather it is very loose in the head
Are there oversized valve guides?
What do I need to keep in mind when I take the heads back to my preferred engineer (Roland Alsop as previously recommended by Charlie at SRR - they did a great job a couple of years ago at re-surfacing the heads the last time)?
Was it the exhaust valve guide?Are there oversized valve guides?
What do I need to keep in mind when I take the heads back to my preferred engineer (Roland Alsop as previously recommended by Charlie at SRR - they did a great job a couple of years ago at re-surfacing the heads the last time)?
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