Rv8 valve guide length - shortening
Discussion
Have run into an unanticipated clearance problem after installing a new cam. Higher lift means the valve spring keepers are now fouling the guide tops/seals - anyone know how much can safely be removed? 10 hole 3.9/TVR400 heads off a 97 build car, later type seals and double valve springs (not sure yet whether they are going coilbound). Such fun 
Boosted LS1 said:
Rover guides are to short as stock but seem to last a reasonable length of time. How much do you need to remove? I'd remove it anyway as the cam you have is bound to have been used before. Or is it a real monster grind?
Well, there's a bit of a story to this but suffice to say for the moment that it's getting there in lift terms and is a new grind on me. Whilst I was anticipating some possible mapping and drivability issues, I didn't think there would be a problem mechanically as my motor is supposed to have been running a 500+ thou lift cam anyway and it was assumed all this stuff would have been sorted to facilitate that. Ahem. Seems the new one has just tipped the balance and maybe things were real close before. The engine was run today but it was obviously not right although I seem to have got away without bending pushrods or breaking any rockers although I have mashed the seal ends...
Answer to your Q Mike is I don't know for sure until I remove the heads and measure stuff against the lift I know the cam generates through the rockers; suppose I was hoping there was a 'standard' shortened length that was just used with high lift cams. Some of the solid lifter cams out there have huge lift and this is still a hydraulic one however so there must be scope to achieve the clearance needed.
The Rover valve guides at 65mm long are much longer than in most other engines, very hard wearing and you can remove as much as you need to obtain clearance without any problem. You start to worry with things like the VW Golf where the guides are only 36mm long as standard and made of a crappy grade of bronze (high spec brass really) and wear out like the clappers even if you don't have to shorten them. In race engines with shortened guides to get better port flow we'd get half a season if that before they were totally shagged.
Obviously if you take them out, shorten the non seal end and refit them a bit deeper in you'll have to get the seats recut because guides are never completely concentric. Easiest way is to press them in a bit further but they tend to be in bloody tight. Using a hammer and drift might bugger the seal end fitment. A hydraulic press will be kinder and not distort the tops.
Not surprising you're having problems with a high lift cam if they are still standard because there's not much clearance to start with.
Might be an opportunity to get a bit of porting done while the guides are out and maybe some nice 3 angled valve seats.
Obviously if you take them out, shorten the non seal end and refit them a bit deeper in you'll have to get the seats recut because guides are never completely concentric. Easiest way is to press them in a bit further but they tend to be in bloody tight. Using a hammer and drift might bugger the seal end fitment. A hydraulic press will be kinder and not distort the tops.
Not surprising you're having problems with a high lift cam if they are still standard because there's not much clearance to start with.
Might be an opportunity to get a bit of porting done while the guides are out and maybe some nice 3 angled valve seats.
Or you could shorten them whilst remaining in the head rather then remove them. Mill the tops down and bin the seals or use the umbrella seals. I've never like those but they may help. Lots of rovers didn't have seals in the first place.
Once you get to the stage of removing guides you may as well fit new ones, buy some shortened bronze items.
As for valve guide length iirc rover guides are comparitevely short compared to the valve stem length. I think there's an ideal ratio somewhere which I once read about. In your instance it's about performance versus mileage and wear. I imagine performance will be the higher priority
Once you get to the stage of removing guides you may as well fit new ones, buy some shortened bronze items.
As for valve guide length iirc rover guides are comparitevely short compared to the valve stem length. I think there's an ideal ratio somewhere which I once read about. In your instance it's about performance versus mileage and wear. I imagine performance will be the higher priority
Edited by Boosted LS1 on Tuesday 15th September 16:46
Boosted LS1 said:
Or you could shorten them whilst remaining in the head rather then remove them. Mill the tops down and bin the seals or use the umbrella seals. I've never like those but they may help. Lots of rovers didn't have seals in the first place.
Once you get to the stage of removing guides you may as well fit new ones, buy some shortened bronze items.
As for valve guide length iirc rover guides are comparitevely short compared to the valve stem length. I think there's an ideal ratio somewhere which I once read about. In your instance it's about performance versus mileage and wear. I imagine performance will be the higher priority
No you don't remember it correctly and no there's no ideal ratio for valve to guide length. The Rover valve at 117mm is a tad longer than in most modern engines but much shorter than say the 135mm valve in the Ford CVH which also has 65mm long guides and also suffers no guide wear in normal use.Once you get to the stage of removing guides you may as well fit new ones, buy some shortened bronze items.
As for valve guide length iirc rover guides are comparitevely short compared to the valve stem length. I think there's an ideal ratio somewhere which I once read about. In your instance it's about performance versus mileage and wear. I imagine performance will be the higher priority
Edited by Boosted LS1 on Tuesday 15th September 16:46
And never recommend bronze guides instead of cast iron ones which last much longer and do just as good a job in every other respect. Bronze guides are a fashion item not a performance one.
spend said:
Stop messing about & get some better heads, the vanilla ones aren't worth it IMHO.
Started pulling the heads tonight 
Good news is it looks like I've been lucky in that pushrods and rockers look straight/intact and any contact has been slight... was worried the cam would end up shagged before it had even run in anger - moral of the story kiddies is don't take anything for granted Thanks for the comments on the guides; that's helpful
Boosted LS1 said:
Why do you think this?
"And never recommend bronze guides instead of cast iron ones which last much longer and do just as good a job in every other respect. Bronze guides are a fashion item not a performance one".
I don't think it, I know it. 30 years of doing this for a living at the cutting edge of race engine design."And never recommend bronze guides instead of cast iron ones which last much longer and do just as good a job in every other respect. Bronze guides are a fashion item not a performance one".
Aksherly if you're sitting comfortably I'll tell you another, yes yet another, little story. Many moons ago I was chatting to a bod at Cosworth about race engine design and valve guides in particular. When the Lotus twin cam came out Cosworth did the road heads with cast iron guides and the race ones with bronze guides. No real reason other than everyone expected race engines to have bronze guides. Trouble is the really good grades of bronze are bar stewards to machine so they picked a crappy grade that was easy to machine like everyone else does including most of the European car manufacturers (VW, Peugeot etc). He freely admitted it was for reasons of cost not longevity.
The bronze guides wore out so bleedin fast that the road heads actually became sought after items for the race crowd. People would pay a premium for them just because the guides lasted several times longer.
Now you can get really hard wearing grades of bronze. For choice if I'm making a custom guide I use aluminium bronze, grade CA104 which shags drills, reamers and lathe tools like buggery when you try to machine it but lasts for ever in an engine. In fact it lasts almost as long as cast iron ha ha.
What most major manufacturers use is a much softer easier to machine grade called high tensile brass, grade CZ114. It cuts like butter and lasts about as long.
Now go to really high output engines like modern jap bike ones. 200 bhp per litre and 15000 rpm. What material do they use for the guides? I'll leave you to guess. Hint - it ain't bronze.
Bronze does technically have a couple of advantages over cast iron. It has a somewhat higher coefficient of thermal conductivity so it's supposed to get rid of heat from the valve a bit quicker but most of that goes out through the valve seat not the guide anyway. It can also be used with valves that don't have chrome plated stems which gall very quickly at high rpm if you use them in cast iron guides. It's easier to plate the valves than change the guides to bronze though and I'm not aware of any modern valve which isn't either chromed or tuftrided as a matter of course. Finally you do get fewer seizures with bronze which is quite a forgiving material in conditions of poor lubrication, hot temperatures etc.
Overall though cast iron is tougher, harder wearing by an order of magnitude, easier to machine and much cheaper. An average iron guide costs a quid or so. A bronze one five or more times that and that's only the crappy grades of bronze. The good stuff costs a bleedin fortune.
Pick any engine that's meant to last for ever - truck or loco diesels for example. What are the guides made of? I really don't need to ask do I?
Pick any car engine with cast iron guides or where the valve runs directly in the iron of the head itself like the Ford Pinto. How much guide wear do you see? Now look at any Eurocrap engine with bronze guides at 50,000 miles. How shagged are the exhaust guides already?
The slanty eyed yeller fellers are now into sintered materials which show some advantages over cast iron but it's still ferrous based. If you want long lasting you don't go copper based. You do that only for fashion and I've never been a follower of fashion. I do what works.
Nuff said.
I could I suppose add a few thoughts on the use and fitment of guides in heads. What many people don't consider, or even realise it needs to be taken into consideration, is the relative coefficients of thermal expansion of the guide and head material. We're dealing with three main materials here. Cast iron, bronze and cast aluminium.
The CoE of iron is about 12, bronze 17 and cast aluminium 22 - all in millionths per degree C. If you fit an iron guide in an aluminium head then it will get looser as the temperature rises. If you fit a bronze guide in an iron head it will get tighter and in an aluminium head just a tad looser.
At a constant temperature you need a certain amount of interference fit to prevent the guide moving. I generally reckon on about 1 thou or a bit more. To that you then need to add any change from ambient temperature to running temperature.
At 200C an iron guide 0.5" in diameter will have expanded 1.2 thou. The guide bore in an aluminium head will have expanded 2.2 thou. Oops! If you fit that guide at only 1 thou interference cold it'll be a nice sliding fit at running temperature and fall straight out.
So you get a range of cold fits dependant on materials that you need to work to and of course it also depends on how hot the head gets.
Iron guide in iron head - 1.25 thou. The fit won't change with temperature.
Bronze guide in iron head - 1.25 thou. The fit can only get tighter but needs to be sufficient when cold.
Bronze guide in aluminium head - 1.5 to 1.75 thou.
Iron guide in aluminium head - 1.75 to 2 thou.
If the guide is long like a CVH with loads of friction holding it in place I can generally get away with a tad less fit than a shorter guide.
The same principles apply when fitting unleaded seat inserts, or just bigger inserts for big valves, into iron and aluminium heads. I use a tighter fit in an ally head to compensate for the expansion effect. In every case I put the sizes, expansion coefficients and expected final temperature into a spreadsheet and calculate the fit I want to work to. I wonder how many general engine reconditioners even understand the principles nevermind be able to do the math.
An average fit for a seat insert which is obviously much larger in diameter than a guide would be between 3 and 4 thou. Maybe as little as 2 thou with a small insert in an iron head. A friend in Guernsey had inserts fitted to a prized Fiat Twin cam race head many years ago by the only machinist over there he could go to. They tried to get the inserts in at 7 thou fit with a big hammer and split the combustion chambers apart. You can't educate pork and tighter ain't always better.
The CoE of iron is about 12, bronze 17 and cast aluminium 22 - all in millionths per degree C. If you fit an iron guide in an aluminium head then it will get looser as the temperature rises. If you fit a bronze guide in an iron head it will get tighter and in an aluminium head just a tad looser.
At a constant temperature you need a certain amount of interference fit to prevent the guide moving. I generally reckon on about 1 thou or a bit more. To that you then need to add any change from ambient temperature to running temperature.
At 200C an iron guide 0.5" in diameter will have expanded 1.2 thou. The guide bore in an aluminium head will have expanded 2.2 thou. Oops! If you fit that guide at only 1 thou interference cold it'll be a nice sliding fit at running temperature and fall straight out.
So you get a range of cold fits dependant on materials that you need to work to and of course it also depends on how hot the head gets.
Iron guide in iron head - 1.25 thou. The fit won't change with temperature.
Bronze guide in iron head - 1.25 thou. The fit can only get tighter but needs to be sufficient when cold.
Bronze guide in aluminium head - 1.5 to 1.75 thou.
Iron guide in aluminium head - 1.75 to 2 thou.
If the guide is long like a CVH with loads of friction holding it in place I can generally get away with a tad less fit than a shorter guide.
The same principles apply when fitting unleaded seat inserts, or just bigger inserts for big valves, into iron and aluminium heads. I use a tighter fit in an ally head to compensate for the expansion effect. In every case I put the sizes, expansion coefficients and expected final temperature into a spreadsheet and calculate the fit I want to work to. I wonder how many general engine reconditioners even understand the principles nevermind be able to do the math.
An average fit for a seat insert which is obviously much larger in diameter than a guide would be between 3 and 4 thou. Maybe as little as 2 thou with a small insert in an iron head. A friend in Guernsey had inserts fitted to a prized Fiat Twin cam race head many years ago by the only machinist over there he could go to. They tried to get the inserts in at 7 thou fit with a big hammer and split the combustion chambers apart. You can't educate pork and tighter ain't always better.
Heads now off.... obvious that the inner valve springs have been going coilbound and several of the seals are displaying damage so we're on the right track. Bit more concerned that the exhaust valves have just been kissing the pistons. Pistons are pocketed and cam was timed up properly (though I'll check it again), just looks like he extra lift has exceeded any headroom I had (thought I had plenty with 400 pistons in a 4.6 block). All straight though and just clean spots on the pistons with no indents so I'm hoping I've not damaged any white metal in the bottom end... phew
GreenV8S said:
Pupp said:
obvious that the inner valve springs have been going coilbound
Any idea how much excess travel there was on the valves?Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff