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Is valve recession a myth?


JohnD
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A recent thread on The Triumph Experience in the US make me ask.   https://www.triumphexp.com/forum/spitfire-and-gt6-forum.8/gt6-mk-i-head-question.1812756/    They are adamant, as it would seem are their valve seats, that the UK obsession with recession in the abscence of lead in fuel is a myth.     Lead was removed from US gasoline long before it was from the UK's fuel, so they have a longer experience, and they deny any valve recesion.      Where's the evidence?

I still think that high-speed motorways, or competion driving does need steel valve seats, but for ordinary quiet classic driving??

John

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Must admit I have thought about this one for a while. I’ve not seen any evidence of seat recession in cars without. Even when lead memory is affected by decoke or other seat lapping.  What do I know. Thought that the engines tended to run hotter, but we live in the uk and most triumphs have permanent fans. Will continue to ignore the seat recession clap trap until there is good reason for modifications.  

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26 minutes ago, JohnD said:

A recent thread on The Triumph Experience in the US make me ask.   https://www.triumphexp.com/forum/spitfire-and-gt6-forum.8/gt6-mk-i-head-question.1812756/    They are adamant, as it would seem are their valve seats, that the UK obsession with recession in the abscence of lead in fuel is a myth.     Lead was removed from US gasoline long before it was from the UK's fuel, so they have a longer experience, and they deny any valve recesion.      Where's the evidence?

I still think that high-speed motorways, or competion driving does need steel valve seats, but for ordinary quiet classic driving??

John

I haven't heard much said about it for years.

I occasionally hear of a car with VSR, but maybe 10 times in as many years? And that is mainly  on CT cars that get very used. 

The other point is one you alluded to. They did get hardened seats from the factory in the states, but no idea when that started. The early 70's would be a fair guess.

Also worth noting that the original valves on Triumphs seem to be high quality and can be used with hardened seats. I have had a few heads converted over the years, and the machine shops were happy to reuse the valves. 

I know the A series engines suffer terribly with VSR if used hard. But indeed, most classics lead a gentle life thesedays (a few exceptions, thankfully)

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I believe the FBHVC conducted trials when 4 star was being phased out and they found that VSR was a reality but!!! they used a quite an old style engine (Morris Minor typwe thing) and they thrashed it to death.

For normal everyday driving/touring VSR may never happen.

 

Roger

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I think they may well be right. There certainly does not appear to be a plethora of evidence to support the theory that lead (or substitute) IS necessary?. Exhaust port (Valve seat) temperatures are IMV going to be a factor in any case, so unless you habitually thrash it within an inch of it`s life?, It`s (again IMV) whilst not remote, highly unlikely.

There is another factor, for many many years we where bombarded with the  "message" that High Compression was the Holy Grail of performance and Lead was an essential element in Premium (and by definition more expensive) Fuels, Blah, Blah. So are we conditioned into thinking that the Engines of that period still must have lead?.

Pete

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I always believed lead to be an agent in raising the octane of fuel and the valve seat protection was only a by-product. I'm wondering if that's why everyone misses leaded, for the performance rather than any physical benefit? 

And - not wishing to sidetrack or drift John's thread - what's today's preferred additive given we only have 95 RON round here?

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Today I removed the head from a Mk1 2L Vitesse engine I have been using for over twenty years at about 2500 to 3000 miles per year without any additive in the petrol. The valves do not looked recesses to me and extremely small leeks into the ports when I filled the combustion  chambers with paraffin.

Reason for removal, head gasket blown between five and six.

Regards

Paul.

 

IMG_20210627_122846.jpg

IMG_20210627_123001.jpg

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Well Paul, Looking at that Head I would concur that VSR is not apparent and the fact that a small amount of byepass after in excess of 50K? Miles is to be expected. I would not have any concern over the lack or not of lead. IF I had any concern I would speculate as to the apparent "impingement" on the head of the valve in No4?.

Pete

 

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21 minutes ago, PeteH said:

Well Paul, Looking at that Head I would concur that VSR is not apparent and the fact that a small amount of byepass after in excess of 50K? Miles is to be expected. I would not have any concern over the lack or not of lead. IF I had any concern I would speculate as to the apparent "impingement" on the head of the valve in No4?.

Pete

 

Before the head gasket failed I had been having a missfire on cold starts which cleared after a few seconds, when I checked the plugs four and five where difficult to remove, replacing them caused a temporary cure. If you look at the first picture some of the waterways are partially blocked and I wonder about local overheating or very minor coolant leak

Link to the post I started on this problem in January.

https://forum.tssc.org.uk/topic/7501-vitesse-2l-mk1-misfire-on-cold-start-now-blown-head-gasket/

Regards

Paul

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It may be related. Water turned to steam at superheated temperatures can do wierd things. It`s got to be experienced to see what damage can be caused in high pressure boilers by just not having the "correct" water/feed conditions.

Pete

 

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5 minutes ago, Colin Lindsay said:

Herald 1200 at about 75000 miles - first time the head had ever been off. I tested the seal with petrol, some drained, most didn't. I haven't replaced the seats, just ground new valves in.

Was thinking of having my cylinder head converted to unleaded spec but after looking at mine and yours Colin will probably not bother.

Regards

Paul

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my 1600 had the seats recut when skimmed to raise the CR  she was driven pretty hard for 15 years and never missed a beat

theres loads of lead memory in the head  i was always taught but my seats were recut 

so from that its myth  same as millennium clock,  unleaded fuel , and im thinking ethanol   , we dont have high levels in 97 ron but whos ever found their carb  has dissolved the only problems we see on here is nasty fuel hose from never land or worse 

Pete   

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The US introduced unleaded much earlier and manufacturers knew this hence US cars had different specs including lower compression pistons etc. It is overplayed, I ran a 1500 engine for years with no issues but would have unleaded inserts if rebuilding the head but only then

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Im expecting to find quite a bit of VSR on my 2L Vit as many of the valve clearances had closed up a LOT on one of my routine checks. This was unusual and I put it down to some running problems I was having at the time: I did about 2k touring miles in Spain with the car running hot due to a poor condition radiator and weak mixture because of leaky carb spindles (not my best trip)☹️

Runs well now its all sorted although still got to check compression readings....

 

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didnt think there was much difference with the result being the valves sit further in the head and your valve clearances close up. Then in the end theres no adjustment left on the tappets😳

Course I dont know if lead or an additive in the fuel would have improved things.... 

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the myth is seat recession  of the head  not valve seat wear   but both will give you your closed up clearances 

and i guess pocketed is different to recessed ???  all a bit similar 

all our engines are aging so something has to give hopefully through usage not myths 

Pete

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I thought VSR was heat causing the valve to 'micro weld' onto the seat everytime it closes and then pulling bits of metal off it. The lead, or substitute, acts as a lubricant between the two so stopping this process. The alternative is hardened seats that resist the microwelding far better...

Dont know what valve seat wear is - flow of gases over the surface causing erosion? 

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24 minutes ago, johny said:

Dont know what valve seat wear is - flow of gases over the surface causing erosion? 

My first car, back in the sixties, a Herald 12/50 some of the valves where nearly oval, perhaps a slight exaggeration but only slightly.

Regards

Paul

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It’s not a complete myth…… unfortunately. Our MkIV Spit has a fairly rampant case right now.

However, the history is that the engine was built from a fairly random collection of used parts to mostly resemble a Mk3 engine, with a big valve Mk IV head. The head was freshened up by lapping the valves and a general tidy up with some light porting. The exhaust valves took a lot of grinding. I was aware that I was chancing recession, but the cure is the same as prevention so….. meh.

Anyway, it lasted about 8k. At about 5k the car had an EFI conversion and not many miles after that the use pattern changed with much more fast, open road work.

First sign of trouble was a blown head gasket between 3&4. I didn’t immediately twig, but did notice that all the exhaust valves were tight (especially 4) when reassembling and then again after torquing the head after 300 miles. Pretty soon after that it started having running issues which we eventually realised were due to no valve clearances on 1 &4 exhaust….. oh yeah, now we get it……

So, at present the state of play is that without additive it does about 250 miles between tappet settings, at which point it’s pretty sick. With additive…… at least 600 and still going strong…..

I previously ran my Vitesse for 25k or so on a standard, well used head with no sign of recession, but did have seats fitted when I ported the head. Even then I’ve recently found the exhaust valves to be 2 thou tighter than the inlets after a hard 20k (4 track days, 3 long continental road trips plus usual running around) and the engine is noticeably crisper with them back where they should be.

So well used standard head with lead memory/work hardening will last well, especially if it doesn’t see too much sustained high power usage. However, grind away that layer and/or use the car hard, and recession gets real soon enough. 
 

I’m repeating the Spitfire experiment on the GT6. It’s ok so far but it’s only done 1100 miles….

Nick

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8 hours ago, 68vitesse said:

My first car, back in the sixties, a Herald 12/50 some of the valves where nearly oval, perhaps a slight exaggeration but only slightly.

Regards

Paul

Ah yes wear to the valves themselves is quite possible with high mileages and especially if valve clearances have been run too tight. In fact if there is VSR the risk is the valves are held open and damaged by burning which is why a compression test is recommended.

In my case the head valve seats had been reground and it going to be interesting when I get the head off one day. However now that the fuel mixture is correct plus engine temperature is much better (on the trip I mentioned it would lift the cap everytime we stopped) and I use an additive for long fast runs the clearances seem to have stabilised so I see no reason to investigate further...

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When the "kit of parts" (my 13/60) arrived the engine had aready been removed. So I have no previous experience to go by. A compression test shows 3 good one low(ish). So The head will eventually come off to see if/what is the cause. When the shell goes for Painting, I expect. However, The Mass of paperwork that came with the car, shows that the head was exchanged via the Club Shop for an Unleaded conversion, Circa June 1999. When the recorded milage was 102000 Miles aprox. according to the `98/`99 MOT`s, so I am not expecting to find VSR.

"Lead" memory is likely to be affected by any major valve work I would have Thought?. The "theory" behind seat errosion was said some years ago to be a combination of high exhaust temp; and the pitting caused by micro welding during closing impact, which the lead was supposed to offset or prevent. And was part the cost driven reason why US cars from the 70`s onward used lower comprssion ratos`s. Meaning the Big US car Makers where not faced with the cost of fitting hardened seats and valves. With the ultra low prices of "Gas. "Efficency" was not at the top of US consumers priority.

Pete

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