Valve stem heights - converting a 295 to unleaded.

[gs.davies]

I'm building up a 295 to go on a 1098 and have bought some valves, unleaded three groove 1" exhaust and a MiniSpares Cooper 998 spec inlet. The inlet stands about 1mm taller even out of the head. Is this a problem? What's the best course of action to take?

[carbon]

I know that the valve stems for valves in early small bore heads ('square collet' type) and early Cooper S are 1/16 inch shorter than the later 1275 valves (single groove).

A+ small bore valve stems may also be of the longer variety? Someone else may be able to confirm.

The tips of the valve stems should ideally all be level.

[gs.davies]

Bit of a better description of the problem and some context on what I'm trying to achieve...

Converting a 12G295 to unleaded...

Any ideas on this please? Having some compatibility problems with some parts obtained from mini spares and wanted to see if anyone has experienced the same issues.

I'm using a plus valves with the triple collet groove in standard valve guides. Exhaust is the standard one inch valve TAM1770 lead free and I have a standard one inch insert (not fitted yet)

Inlets are the C-AEG588 valve which is the same size as the standard 12G295. I selected that one as it's also supposed to be compatible with lead free fuel.

A couple of problems;

1. The stem height of the inlets is about a mm higher. Is this significant?
2. The inlet valve on closer inspection is made of EN214N. The companion exhaust valve is the same material but requires a manganese/silicon guide. Further, the companion exhaust valve is 1.040" - does this cause a machining problem for the hardened insert?

All I want is an unleaded 12G295. We've fitted new guides and reamed, were at the stage where it's time to have inserts fitted and have seats cut.

Should I be using these valves, or would I be better off returning the a plus components for standard a series parts? Will simply having a hardened insert be sufficient to run on corrosive modern fuel?

[Spider]

You can use your original Exhaust Valves (if they are Servicable) or direct replacements. There's no issue using these with Unleaded Fuels.

It's the Seat in the Head that needs to be 'up-rated' usually by fitting an insert (as you are already doing).

As Carbon has said, the Valves ideally need to have their tips at the same height. You can fit it, should be able to adjust the tappets and get it running OK, but you won't get the best from the Cam with them that far out.

[gs.davies]

The exhausts are standard replacements - the head was bought completely bare. It's the inlets I'm getting tangled up with. I've got A-plus C-AEG588 which apparently are designed for unleaded fuel. What's puzzling me is that INLET valves are being specced as being suitable for unleaded.. Why is this? I thought that the unleaded problem was sorted by the installation of a hardened insert. Presuming that the biofuel these days causes oil dilution problems on the stems?

I think the 1mm out is too much to bear, especially given that the head's been skimmed and will require the rocker posts shimming too. I shall probably take them back along with the A Plus valves and go with the single groove old style replacements IF I can be sure I'm not missing something important to do with modern fuel.

[Spider]

I've got A-plus C-AEG588 which apparently are designed for unleaded fuel. What's puzzling me is that INLET valves are being specced as being suitable for unleaded.. Why is this?

Good question.

Exhaust, yes, Inlets, well, I've been fitting and using the Same Inlets that I was with Leaded Fuels for Unleaded use. In regards to Hardened Seats, I've only ever fitted them to the Exhausts, only ever dressed the Cast Iron Inlet Seats (in the heads). Rover did the same in later days, when they produced the engines for unleaded fuels.

[gs.davies]

So, it seems that the only unleaded 1" exhaust valve is the TAM1770 which is a three groove collet. There's not a 'matching' lead free inlet.

The only option appears to be this;

A plus three groove collet exhaust valve with an a series 12G296 equivalent inlet and it's appropriate cap and collet.


Then I'm mixing up collet types on the head. Is this a problem?

Otherwise the only option it would seem is to remove the guides I just pressed in and replace with the manganese silicon ones, obtain the companion exhaust which is 1 1/16 and have the inserts machined to accept it.

Any thoughts on this?

[Spider]

OK, I'd suggest these parts;-

Inlets https://www.minispares.com/product/Clas ... |Back%20to

Exhausts https://www.minispares.com/product/Clas ... o%20search

Exhaust Seats (for Unleaded conversion) https://www.minispares.com/product/Clas ... |Back%20to

In regards to Valve Guides, plain standard Cast Iron.

That combination of parts will be fine for Unleaded use and you'll be able to get your Valve heights more acceptable.

[ianh1968]

Personally, if this is a fairly normal road engine, I would not be overly worried
about the height difference. But I would expect all the inlet heights to be the
same and all the exhaust heights to be the same...

We can take a punt that the original cam/head/pillars/rockers setup
MAY have been optimised at the factory, but I certainly would not want to
put money on this. Add into the mix that the head may have been skimmed,
perhaps more than once, and the cam may be different and will have a base
circle of a different size. Yet more things to consider would be the socket
depth in the cam followers and the pushrod length. And of course, the ratio
of the rockers themselves can vary, not only between different types, but
also between different specimens of the same type.

Valve train geometry is one of those aspects where unless you actually try
various permutations of pillar height etc, and then measure the results with
a dial gauge, you will never know for sure if things are better or worse.

Having the inlets/exhaust valves 1mm different may actually be an improvement.
What is really needed here is a before/after measuring session...
(Has anyone got a time-machine?)

I would only really be concerned about the tip heights if this would also
cause the valves to be either under sprung or coil-binding is occurring.
The former would reduce the rev capability, the latter would also cause
damage to the valve-train which could be catastrophic.

As regards the size being 1.040". There are two reasons for this size:

1) There is a fairly good chance on a standard head that the seats are
well and truly sunk into the head after several re-cuts. Using a slightly
larger valve will enable the seats to be re-cut to a sensible width, ie
reduced, by boring out the pocket to an appropriate size.

OK, when hardened seats are fitted, this is less of a problem...

2) This is the largest (nominal) size of exhaust valve that will fit down
a 998/1098cc STANDARD bore without block modifications.
A 1&1/16" (1.0625"/27mm) valve will require pockets and the amount of cut
required varies between the inner and outer cylinders because the bores
and the chambers do not line up.

Other than making sure that the caps/collets are matched, having different
inlet and exhaust setups should not be a problem.

Both Spider and I both agree that using stem seals on ALL valves is the way
to go. (But we all have our own ideas and theories on this!).

Ian

[gs.davies]

I know that a nominal five thou was taken off the top of the head (rocker side) to ensure it was level. This was done by an aircraft engineer. Measurements prior to this showed that 70 thou has been taken off the chamber side, a further five thou was taken off to level it off. So, eighty thou off in all and therefore the rocker posts will require shimming to maintain the notional correct geometry.

I've more or less decided to go with spiders suggestion of reverting to the original type valves with hardened inserts and I'm aiming to get it To a machinist this weekend to insert and cut the seats.

i need to measure the capacity of the chambers too at some point before completing the build. I'll be having the block refaced by the minimum to get it flat so knowing the cc of the chamber should enable me to calculate the final CR.

It's a Normal road engine, 1098 with a 997 spec cam in place of the 850 but still atop a wand box.

[ianh1968]

So, eighty thou off in all

That's quite a chunk...

and therefore the rocker posts will require shimming
to maintain the notional correct geometry.

Why not make up a few different thicknesses of shims and try them out?
Say, for example, in 20 thou increments...

You could then optimise the geometry and the "notional correct geometry"
will become totally academic.

You would not even need to do anything fancy, a batch of 3/8" flat washers
would do in place of proper shims, even for the 5/16" studs. You won't be
running the engine like this, just measuring the lift with a dial gauge...

If you find that what ever you do makes it worse, you may need to shorten
the pillars, not make them taller.

Once you've worked out the optimum, get the proper shims made.

Good Luck - I am sure that it will all work out fine!

Ian

[gs.davies]

I think that's pretty typical for a 295 on an engine with dished Pistons - as I said still got to work out the actual cr to make sure it's not miles off but anecdotal evidence suggests it'll be ok.

Good idea with the experimentation - I'll give that some consideration along with the other bits of engine work I've got planned.

[gs.davies]

Off to MiniSpares in the morning to collect the replacement valves. I have four top hat type stem seals that came with the MiniSport cam kit. I've just raided an old 850 head for it's 1/4 inch caps and collets and of course the seals are the probably useless o ring type.

Earlier in this thread a couple of you mentioned valve guide seals - can I use the top hat seals in conjunction with the 850 type cap and stem shroud arrangement? Or should I fit the O rings and wait for them to fail in no time at all. Or should I just not bother and have a little bit of smoke in keeping with the period?

Gary

[rich@minispares.com]

Why not make up a few different thicknesses of shims and try them out?
Say, for example, in 20 thou increments...

You could then optimise the geometry and the "notional correct geometry"
will become totally academic.

You would not even need to do anything fancy, a batch of 3/8" flat washers
would do in place of proper shims, even for the 5/16" studs. You won't be
running the engine like this, just measuring the lift with a dial gauge...

If you find that what ever you do makes it worse, you may need to shorten
the pillars, not make them taller.

Once you've worked out the optimum, get the proper shims made.

Good Luck - I am sure that it will all work out fine!

Ian

don't forget that you may need to alter the length of the pushrods as well if your moving the posts up or down.

otherwise you may find that the rocker screws are rammed hard up into the rockers, or right at the end of their limits - which can stress them and snap the balls off

[mk1]

which can stress them and snap the balls off

OUCH!

[gs.davies]

Earlier in this thread a couple of you mentioned valve guide seals - can I use the top hat seals in conjunction with the 850 type cap and stem shroud arrangement? Or should I fit the O rings and wait for them to fail in no time at all. Or should I just not bother and have a little bit of smoke in keeping with the period?

Gary

Thread resurrection..! I stumbled across this thread after googling for unleaded 295 heads and thought the tale was familiar. If only your older self could tell your younger self tales from the future!

Anyway, I did eventually fit the ordinary top hat seals on the inlets only along with the top caps and shrouds. Here's what happened next (after several thousands of miles and galloping oil consumption which by last week was around a pint per 70 miles...?)

DON'T fit the shrouds with the top hat type seals. The shrouds catch the seal, in the case of number one, ripping it. At best, they'll act as a pump, forcing oil down onto the top of the seal and eventually past it and into the chamber, leading to the sorry mess you can see in the chambers and on the back of the inlet valve.

The blown head gasket is just for fun, the lord only knows how this car was still running! The odd oil leak that tracked round the top of the block and pooled under the engine number was tracked to the oil feed leaking past the gasket. No coolant was used, no pressurisation, no oil/water mixing. John's now proven to be right with his insistence in finding a can of Barrs Leaks on the run down to IMM last year and it's probably 'the turd' that's kept it going all this while!

Anyway, the head's now been through the wash along with the inlet valves and are now nice and clean, no nasties on the block or head faces, so with a new set of exhausts (pitted..), Viton seals on all eight valves lapped in and a decent gasket, this will all go again. Hoping for a rather more conservative approach to the use of oil now!

I might even repeat the leak down test done a couple of weeks ago at Rolesyboy's place and see what's what. I wonder if it'll go any better now?

Here's what happens when you fit shrouded valve caps with the top hat seals..

IMG_7612.jpeg

IMG_7610.jpeg

IMG_7609.jpeg

1712B804-B7E8-420C-B5AC-5555C31D8A47.jpeg

[Exminiman]

Why not make up a few different thicknesses of shims and try them out?
Say, for example, in 20 thou increments...

You could then optimise the geometry and the "notional correct geometry"
will become totally academic.

You would not even need to do anything fancy, a batch of 3/8" flat washers
would do in place of proper shims, even for the 5/16" studs. You won't be
running the engine like this, just measuring the lift with a dial gauge...

If you find that what ever you do makes it worse, you may need to shorten
the pillars, not make them taller.

Once you've worked out the optimum, get the proper shims made.

Good Luck - I am sure that it will all work out fine!

Ian

don't forget that you may need to alter the length of the pushrods as well if your moving the posts up or down.

otherwise you may find that the rocker screws are rammed hard up into the rockers, or right at the end of their limits - which can stress them and snap the balls off

Is this all ok ? Also ( you may of already done this) but might be worth checking the CC of the chambers and calculating the static CR.

[gs.davies]

In the end I slung it together without investigating the rocker heights. It will go back together with a set of shims but given the planned change to a 1300 for this car in early 2025, apart from solving the head gasket and valve guide se problem, I’m not going any further into it. Might check the cam timing, that’s about it.

CR calculates to about 8.9:1. Can’t really go any more than that given the standard pistons or without decking the block. Pistons are 20 thou down the bore.

[mowog]

12G295 Head Posted for Steve (CTR)

[CooperTune]

This is one of my 295 cyl heads. After a good cleaning, new cast valve guides, hard seats, C-AEG587 exhaust and C-AEG588 intakes. The retainers and keepers are late A+. The springs are correct for the camshaft. I build my 998s in A+ 998 blocks bored to .060 using late flat top press fit pistons and rods. Zero deck the block CC the head and surface for 10.2 CR. I'm running out of 295 castings. Steve (CTR)