Twin Cam cylinder head

[Gizze]

Hi,
I'm refurbishing my twin cam, and I have a question with regard to the head. The head is now stripped bare, and having removed the valves and springs I've found one spring seat can be spun around the valve guide, and is in fact proud whereas the others seem to be seated much lower. Once re fitted with the valve, will the pressure of the spring re seat it, or is there something else I should do before re assembly?
Any suggestions would be gratefully received.

[ardee_selby]

Gizze,

Did you see this thread?

elan-f15/loose-valve-guide-t22263-30.html

It included this pic:

VALVE ASSY.jpg (33.31 KiB) Viewed 2020 times

Could you clarify what you see as being "proud"? (Not wishing to be a "Jobs' Comforter" here, but any sign of that valve guide having moved compared to others?)

Cheers - Richard

[Gizze]

Hi Richard,
Many thanks for the quick reply. I hadn't seen this post.
The head has just returned from a machine shop. They didn't remove the guides but they were worn, so they drilled (reamed) out the holes and fitted inserts along with new valve seats. I assume they've checked that the original guide hasn't moved.
In comparison to the other valve spring seats this one is not so far down in the head (ie further away from the combustion chamber). Tomorrow I'll see if I can lift the seat out and check the spring clip is in place on the guide. However if it's not I assume the guide needs to be withdrawn to fit it, which will mean it will need to go back to the machine shop, as I don't think I'll be popular with the home oven option discussed in the previous posting!
Regards
Gizze

[elansprint71]

Hi Richard,
Many thanks for the quick reply. I hadn't seen this post.
The head has just returned from a machine shop. They didn't remove the guides but they were worn, so they drilled (reamed) out the holes and fitted inserts along with new valve seats. I assume they've checked that the original guide hasn't moved.
In comparison to the other valve spring seats this one is not so far down in the head (ie further away from the combustion chamber). Tomorrow I'll see if I can lift the seat out and check the spring clip is in place on the guide. However if it's not I assume the guide needs to be withdrawn to fit it, which will mean it will need to go back to the machine shop, as I don't think I'll be popular with the home oven option discussed in the previous posting!
Regards
Gizze

Gizze,
As the perpetrator of the other thread I'm puzzled by what you have written (highlighted above).

I can't remember (without reading all of it) exactly what conclusions were reached in that thread about the usefulness of the original design but I would never, ever, use those stupid bits of wire again (erroneously referred to as "circlips" in the manual).
The shouldered valve guides from JAE (and others) are a proper engineering solution, that is the way to go.

The oven thing is not too bad, just remember the fish. On reflection, curried fish would be better.

PM me if you need a steer.

[AHM]

I've also got a head striped.

It also had 1 circlip placed to hold the spring seat in!

How do the non circlip guides prevent the guide from coming up?

I have read about cracks in the head - What cracks should I look for?


thanks,

Simon

[rgh0]

I have seen 2 types of spring seats used and various issues with them.

Original style - located by lip on outer edge into the bored lip on spring pocket. The hole is the centre of the original ones of this style was large enough to clear the orginal circlip on the original valve guide. A larger circlip or locating ridge on the guide (which also may be oversize in OD) or a smaller hole in the seat than orginal may cause a problem with interference and the spring seat not fitting correctly

Alternative style - located by a lip on the central hole. The lip needs to be formed to clear the locating circlip or ridge on the guide or to use the circlip or lip as the locating point rather than the guide itself. depending on changes made when rebuilding and fittng this alternate style seat this seat may no longer fit if a guide has been changed in a subsequent rebuild

Over the years machine shops rebuilding Lotus head have tended to use what they have available and if they did not have original style parts they used near alternatives that could be made to fit OK or maybe not so OK. Given the multiple rebuilds that many heads have had over 40 ro 50 years and depending on what they did, you can have problems when subsequent standard components or further non standard components that do not fit with the previous mods done.

cheers
Rohan

[rgh0]

I've also got a head striped.

It also had 1 circlip placed to hold the spring seat in!

How do the non circlip guides prevent the guide from coming up?

I have read about cracks in the head - What cracks should I look for?


thanks,

Simon

The circlip or fix lip is just there so you know when to stop pressing a new guide in place and you have it the right depth in the head. The guide is held in place by the interference fit

The cracks typical run from the valve seats to the spark plug hole and are generally not an issue as they dont run deep enough to go though into water jackets or the ports

cheers
Rohan

[elansprint71]

I've also got a head striped.

It also had 1 circlip placed to hold the spring seat in!

How do the non circlip guides prevent the guide from coming up?

I have read about cracks in the head - What cracks should I look for?


thanks,

Simon

As Rohan stated the "circlip" is just a marker to tell you when the valve guide is in position. It should not hold the spring seat (as I mistakenly thought early on in the other thread when I/we were not sure what were dealing with). What holds the spring seat in position is a pair of hefty valve springs! That seat ain't going no place soon.

The interference fit prevents the guides from coming up (or down), they are , in layman's terms a tight fit, that's why the head has to be heated to get them in or out. If they are loose (as one of mine was, see other thread) then oversize (O/D) guides are available. At JAE, form memory, it was +0.002 and +0.005.

[elj221c]

They didn't remove the guides but they were worn, so they drilled (reamed) out the holes and fitted inserts along with new valve seats. I assume they've checked that the original guide hasn't moved.

Gizze,
As the perpetrator of the other thread I'm puzzled by what you have written (highlighted above).

Likewise. Sounds like a bodge to me!

[Gizze]

Hi,
To explain the valve guides first: the guides were drilled / reamed out, then for want of a better word, sleeves inserted which restored the required diameter of the valve guide. I was also sceptical and so did ask but was assured it was an acceptable way of restoring the head. This wasn't a 'back street' engine recon shop, but a well established business that anybody in my area would know. However as always I'd appreciate others comments ...
Circlip - Having now managed to look under the valve seat, I can see the circlip is no longer there, and neither can I see it anywhere else, so I'm now planning to 'rod' the oil galleries to check it's not stuck somewhere.
Once again many thanks, great forum
Gizze

[ardee_selby]

Hi Gizze...

To explain the valve guides first: the guides were drilled / reamed out, then for want of a better word, sleeves inserted which restored the required diameter of the valve guide. I was also sceptical and so did ask but was assured it was an acceptable way of restoring the head. This wasn't a 'back street' engine recon shop, but a well established business that anybody in my area would know. However as always I'd appreciate others comments ...

My interpretation was that the head had been reamed to allow oversize guides. Common enough. But I'm intrigued by this. Never come across it before (on any engine type). My immediate thoughts are: There's not enough "meat" in the guides to result in an insert of any thickness, but if so, how are the inserts retained?

Circlip - Having now managed to look under the valve seat, I can see the circlip is no longer there, and neither can I see it anywhere else, so I'm now planning to 'rod' the oil galleries to check it's not stuck somewhere. Once again many thanks, great forum Gizze

My first idea was that the circlip WAS in position & perhaps the guide hadn't gone fully home so was interfering with the seat(ing). Again...

Any chance of some pics?

Good Luck - Richard

[Orsom Weels]

Hi Gizze,
I've never heard of guides being resleeved either, like richard, I'm intrigued, &, if there's no circlip, have you found out what is holding the spring seat up ?

All the best, Tim

[rgh0]

Putting inserts in valve guides is a relatively common overhaul technique. In Australia at least they are called K-line inserts. The guide is reamed the K-line insert installed and then the insert reamed to size.

Given the close tolerances required and no oil seals on a twin cam it would have to be done very carefully by a competent shop to get acceptable results. The short length of the twin cam guides and the relative softness of the inserts also means a shorter life than a new guide.

cheers
Rohan

[ardee_selby]

Putting inserts in valve guides is a relatively common overhaul technique. In Australia at least they are called K-line inserts. The guide is reamed the K-line insert installed and then the insert reamed to size.

Given the close tolerances required and no oil seals on a twin cam it would have to be done very carefully by a competent shop to get acceptable results. The short length of the twin cam guides and the relative softness of the inserts also means a shorter life than a new guide.

cheers
Rohan

Rohan,

Interesting. Something new (to me at least).
When would that be chosen over replacing the guide? Also, how are they retained? Shrink fit within the old guide?

Cheers - Richard

[rgh0]

They are a press fit into the guide using a special tool that inserts into the liner. They are used because they are cheaper and I presume quicker to fit than new guides.

See the link below for some details - made in the USA
http://klineind.com/Valve-Guide-Liner-R-System.html

cheers
Rohan