Valve stem seals

[Guest ron]

Hi All

After fitting an unleaded head with bronze valve guides during the winter I find I am burning a little oil after an overrun. As the head had no stem seals fitted as supplied I was thinking of fitting a set of late MG ones to the inlets.

Now the Moss catalogue gives an Indian rope trick method of doing this without removing the head but I was thinking of adapting an old spark plug to fit an air hose and holding the valves shut using air pressure. Does anyone have any comments/suggestions about this method? and does anyone have any experience of running the TR engine with valve seals.

I don't have an auxiliary oil feed pipe fitted and at a rough guess I'm getting 650/700 miles to the pint.

Ron

[jonlar]

650/700 to the pint - I'd suggest there's no problem with that.

 

With the Moss Indian rope trick, yes, I can see that'll stop any valves dropping, but I don't know how the valve spring can be compressed to allow the collets to be released ? ? ? ? ? ? ?

[Richard Crawley]

650/700 to the pint - I'd suggest there's no problem with that.

 

With the Moss Indian rope trick, yes, I can see that'll stop any valves dropping, but I don't know how the valve spring can be compressed to allow the collets to be released ? ? ? ? ? ? ?

Ron,

I have never burned 650/700 to a pint of oil & this is excessive, around a 1/2 litre top up between 3000 mile oil changes is nearer the mark & that’s with some good thrashing sessions! Two of the specialists I spoke to before getting my head converted advised against fitting bronze valve guides. Apparently their different thermal expansion characteristics means they have to have higher clearances otherwise they can stick when hot. It does not take much to work out that wider clearances means more oil is likely to find its way down the valve stem, particularly before it is fully warmed up. I assume your oil consumption was OK before the head work? You can try fitting valve stem seals & this should help but I have no experience with these on a TR engine.

With the Indian rope trick you need a tool comprising the collet side of a spring compressor fitted to something you can push down on very hard, fairly strong muscles & an assistant to flick out the collets while you go bright red in the face!

[Guest ron]

Hi Guys

Thanks for the response.

The oil consumption I quoted was a guesstimate but it is definately a lot poorer than it was last year, it is now coming up to 5000m since the rebuild so it should be nicely run in and I would be expecting oil consumption to be similar to what Richard suggests.

Richard, didn't know about the bronze guide clearance but I'm stuck with them now so I'll try the late MGB seals on the inlets.

Jon, there is a special tool available to do this, it basically hooks onto any spare stud, or you can put the rocker shaft on without rockers and hook it onto that, you lean down on it similar to Richards' suggestion but hopefully without the bright red face!!

I have the same setup of valves, seals and guides on my MGB and I'm getting over 1000m to the pint so hopefully this should help.

Only trouble at the moment is the weather is lovely so I'd rather drive it than tinker with it!! :cool:

Ron

[john.r.davies]

Ron,

Valve guides letting oil into the chamber are not the only cause of smoke on the overrun.   The other is poorly sealing piston rings.

 

You have "the same setup" on your B with no problem.    Did the TR work include new piston rings?  And if so were the bores deglazed/honed?   And if so, did you run in the new bores?

 

If they are letting oil up, they may let gas down - have a look through the oil filler - is there an out-draught of gas, or just a breeze?

John

[Guest ron]

Hi John

I'm reasonably confident that the oil is going down the inlet valve guides as the problem wasn't there with the original head, also when I changed the head at 3000m the bores were bedding in nicely.

Ron

[Andy Moltu]

There are valve spring compressors that you can use without taking the head off.

Making sure that the piston is at top dead centre will obviate the need for compressed air / string fed through the bores.

[Guest ron]

Hi All

That's the stem seals fitted, it certainly wasn't the easiest job I've ever done so I hope it works.

If anyone else is thinking of trying it, the proper tool is a must, it hooks round the rocker shaft and you don't need to remove or dimantle the rocker assy.

I used the indian rope trick and it works quite well, I couldn't be bothered making a compressed air adapter, but I think it would work better. I don't think Andy's suggestion of the piston at TDC would work, the valve would drop too far.

As is usual for this type of job it took about the same time to do the first one as it did for the next five altogether, and the whole job took just over 2 hours.

Ron

[jonlar]

Well done Ron. let us know the results - good luck.

[Andy Moltu]

I don't think Andy's suggestion of the piston at TDC would work, the valve would drop too far.

It does work I've done it! A length of dowel through the plug hole will give extra lift if needed.

[Guest ron]

It does work I've done it! A length of dowel through the plug hole will give extra lift if needed.

Andy

How many hands have you? I needed one for the compressor and the other to fiddle the collets in, and that was a big enough hassle without having to wiggle a dowel as well,  no doubt you managed it but it's a lot easier with the rope or compressed air.

Ron

[Andy Moltu]

You don't need to hold the dowel! But a third hand would make the job easier!

[Peter Douglas Winn]

Spend some money and buy from Snap-On the correct tool.

[jonlar]

Spend some money and buy from Snap-On the correct tool.

There is such a thing?  What's the tool part number and how much is it?   just seeing Snap-On scares my plastic!

[Guest ron]

Spend some money

I'm a Scotsman, no swearing on the forum please

 

Ron

[Peter Douglas Winn]

I think you can find what you want in this area.

Good luck!

 

 

http://buy1.snapon.com/catalog....tBrowse

[Guest ron]

Well the cars now done 250 miles since I fitted the seals and it looks like a result, the oil level on the dipstick has hardly moved at all.

Ron

[Guest Neil Russell]

So your machinist was not so good then? Seems like the tolerance down the guide was a little too big.

Neil.

[Andy Moltu]

The clearances on bronze guides tend to be larger than on the OEM guides.

[Guest ron]

I would tend to agree with Neill, don't know whether they're not very good or just not taking any chances, but the clearance seems excessive to me, even allowing for the different coefficients of expansion.

Ron

[Tom Fremont]

Racetorations supplied me with a head with bronze guides, and oil consumption holds around 1 ( US ) quart per 2000 miles - with an auxilliary oil supply line to the rocker shaft, no valve guide seals, and a PCV valve drawing crankcase fumes/oil mist into the inlet manifold.

 

I'm happy to have a little oil get between the valves and the guides.....  ::

[Guest Neil Russell]

I don't think that the quantities of oil consumed are anything to worry about Ron. truth be known is that even the same engine can differ across the range in terms of production tolerances.

 

I ran a 2.8 quattro A4 and I have an S4 bi-turbo now. The handbook stated quite clearly that 1ltr of oil every thousand miles would be consumed. my old 2.8 used to consume it, my new S4 never needs a top up between major service intervals, same engine?

 

Machining guides however is a different matter. if a clearance between a valve and guide is such that it allows oil to seep down it then this is never a good thing. excess clearance allows the valve to wobble in the guide, all this does is cause the guide to wear further and faster. anyone who convinces themselves that a little bit of oil seepage is a good thing is only going to be disapointed that much more sooner than the person who had a head correctly built, they will also be significantly down on power.

 

The fault lies with the machining.

The machinist hasn't allowed for the correct expansion between guide and valve and machined it to big.

 

The reason we use phosphor bronze guides is that a tighter tolerance (after allowance is made for expansion) can be run between valve and guide. making for a better gas seal and allowing the use of higher lift cams often with shorter duration. These cams cause higher side loads on a valve and this is taken up by phosphor bronze in the form of a tighter clearance and a metal which provides a natural lubricant. Oil also reduces the octane rating of fuel so you really don't want it going down a guide.

anyone who has built an engine with phosphor bronze guides, which does not use any of the above theory to extract more power really has wasted their money.

 

The sad fact today is that people often read about phosphor bronze being the best, but they do not realise why it is the best or in what applications it should be used. For a mild engine, Richard had the right idea and stuck with cast iron guides.

 

I am sorry you have had a bad experience Ron, but it highlights that a good engine build is light years away from many an engine reconditioner. and also that people can come unstuck unwittingly thinking they are choosing the best, when the best was inappropriate.

 

I think that your machinist has let you down because of his lack of knowledge with respect to the materials he has used. its not going to cause you any grief, but it has cost you a strip down and a set of stem seals. I hope you didn't pay too much for the work.

 

Neil.

[Andy Moltu]

How many modern cars are not fitted with valve stem seals? Even with tight modern tolerances.

OK the 6 has an overhead valve design rather than overhead cam like most moderns but still pumps pleanty of oil up into the rocker gear. (Always puzzled me why some feel the need to fit auxillary rocker oil feeds - with decent oil pressure and clear oilways there should be plenty of oil delivered to the rocker gear by the standard set up.)

 

Apparently Triumph felt that 200 - 500 miles per pint of engine oil was within normal limits when the cars were new.

[Guest ron]

Neil

I was under the impression that the main reason for using Phosphor Bronze in unleaded conversions was due to it's superior ability to transfer heat away from the valves which run at a higher temperature on unleaded, after all cast iron is a good guide metal in its own right as it also has good self lubricating properties. Being a cynic I reckon the most likely reason for someone recommending CI over PB is cost.

I'm not even sure the machinist has 'let me down' as you say, it looks to me a deliberate decision as they are very consistent, after all sticking a reamer down a guide isn't exactly rocket science.

It might not even have been a problem on a PI car as they run at a much lower engine vac than carb cars, anyway it cost me £1.20 and a couple of hours work so it's not the end of the world.

By the way how's your TVR conversion coming on?

Ron

Ron

[ushes]

I've done a similar 'rope trick' numerous times on the old Datsun 120Y.  If no compressed air is available, get the piston to TDC and get an assistant to hold the valve up using a bent/blunt screwdriver through the plug hole.  A couple of sharp taps using a plug socket on the valve collet retainer usually releases the collets.  Obviously there's a risk that they might fall into the engine somewhere so plug all holes, but if the socket is held onto the retainer firmly they are usually held within the socket.  I've done it loads of times without losing any collets.

 

Regards

Steve