Valve seat inserts and E10 fuel

[Ian J]

Hi
I'm in a slight dilemma and am hoping for some advice.

I have a 1973 +2 with the big valve cylinder head. My questions are,

1) Are the standard inserts able to withstand using unleaded fuel. My understanding is that they are cast iron and therefore will be a problem if the engine is used at high revs ie anything above about 3000 even with a good addictive such as TetraBOOST. Or could I get away with just using an additive with the standard valve seats.

2) Are phosphor bronze valve guides also necessary to with stand the heat issue with unleaded fuel?

3) Can any one recommend a machine shop in the South East for the valve seat inserts and head rebuild? Ideally that understand Lotus Twin cams

[Craven]

If you are considering replacement valve guides look into fitting phosphor bronze liners.
Results in much less valve seat work.

[rgh0]

The standard Lotus Twincam will run for many years on unleaded fuel without modification or excessive valve seat recession. The standard Valve seat inserts even if you still have the originals which is not common by now, were hard enough, but a lot of engine rebuild shops made lots of money recommending replacing them over the years for no good reason. If the engine is running OK and valve clearances and shims OK now, then there is no specific need to replace the seats due to using unleaded fuel

The standard original cast iron guides wore relatively quickly to the point of oil burning. This was not due to leaded versus unleaded fuel but due to their length being marginal and lack of any stem seal requiring the inlet valve clearances to be maintained very tight and small amounts of wear leading to excessive oil leakage into the inlets and older mineral lubricating oils not being very good. With good assembly and modern synthetic oils and modern materials the valve guides if needing replacement even if replaced with standard cast iron should last well over 50k miles. But if doing a guide replacement I would replace them with the modern bronze alloy guides as the cost is essentially the same and they will last twice as long.

cheers
Rohan

[2cams70]

If you are considering replacement valve guides look into fitting phosphor bronze liners.
Results in much less valve seat work.

These are known as “K-lines”. I’ve had them fitted to cross flow engines in the past without issue. You do not have to have the existing valve guides removed to fit these.

[rgh0]

If you are considering replacement valve guides look into fitting phosphor bronze liners.
Results in much less valve seat work.

These are known as “K-lines”. I’ve had them fitted to cross flow engines in the past without issue. You do not have to have the existing valve guides removed to fit these.

While they can be successfully fitted to Twincams, getting the inlet clearances reamed right is challenging and harder than with new guides which is hard enough. You want a firm that understands Twincams and will try to work at the lower end of the valve guide to stem clearance.

cheers
Rohan

[2cams70]

Yes you have to be careful with clearances. You most certainly don't want not enough clearance regardless of what type of guide is used. In this instance the valve stem (usually exhaust) will expand in it's guide and seize in which case you'll likely end up with a right old very expensive mess.

[h20hamelan]

good stuff
thanks Gentz'

[rgh0]

Yes you have to be careful with clearances. You most certainly don't want not enough clearance regardless of what type of guide is used. In this instance the valve stem (usually exhaust) will expand in it's guide and seize in which case you'll likely end up with a right old very expensive mess.

Yes I use bronze alloy guides and set the inlets in the bottom half of the tolerance range to minimise oil leakage and exhausts in the top half of the range to minimise seizing risk which is especially important in race engines due to how hot the exhausts run. So far its worked well for me

cheers
Rohan

[Craven]

I was told the advantage of fitting liners being the head is subjected to far less stress and possible damage as the iron guides remain, alignment between guide and valve seat stays very much the same therefor less reseating of the valve retaining good tappet clearances. Obviously if new valve seats are being fitted not so important, but if it’s excessive smoke or whatever from worn guilds then liners are a cost effective fix.

[promotor]

I was told the advantage of fitting liners being the head is subjected to far less stress and possible damage as the iron guides remain, alignment between guide and valve seat stays very much the same therefor less reseating of the valve retaining good tappet clearances. Obviously if new valve seats are being fitted not so important, but if it’s excessive smoke or whatever from worn guilds then liners are a cost effective fix.

I have to say despite the T/C heads I owned having had complete bronze guide "bullets" fitted and never had K-lines fitted I agree that liners in the guides if done right seem a good way to go even if changing valve seats - hopefully you'd manage to keep all of the geometry straight and not stress the head when replacing a complete guide. I notice that whenever bronze guides are fitted there's always some aluminium smeared on the guide outers when viewed from ports (ie the part that has passed through the head) which shows material is quite clearly coming off, even if in minute amounts. When you're only dealing with no more than 0.0015" interference fit it does make me wonder how much is coming off the head when you fit them even when warming the head and freezing the guides!

[alan.barker]

Imho the only way to fit new valve Guides is to heat the Cylinder head and cool the Guides in Liquid Nitrogen.
Then they fall into place with no scuffing of the Alloy by the Guides.
Alan

[promotor]

Imho the only way to fit new valve Guides is to heat the Cylinder head and cool the Guides in Liquid Nitrogen.
Then they fall into place with no scuffing of the Alloy by the Guides.
Alan

Hello Alan. Have you seen this done? I've been in workshops where this has been done (warm head, liquid nitrogen for guides) and they still needed knocking in so I guess they didn't get the head hot enough and guides cold enough !

[Andy8421]

I was told the advantage of fitting liners being the head is subjected to far less stress and possible damage as the iron guides remain, alignment between guide and valve seat stays very much the same therefor less reseating of the valve retaining good tappet clearances. Obviously if new valve seats are being fitted not so important, but if it’s excessive smoke or whatever from worn guilds then liners are a cost effective fix.

I haven't tried K-Line liners in a Twinc, but valve guide liners are a common fix in the US for worn guides. I replaced a set of K-Lines on my Son's (horrible) Mercruiser boat engine. 4.5 litre, four cylinder - the pistons were the size of dinner plates.

The guides have to be drilled to take the liners, so unless you are lucky you will lose the registration with the valve seat and the seat will need to be recut. In my Son's case the liners had been forced out by rusty valve stems, so it was just a case of replacing the liner and the valve. After being forced in to place, a precision broach is driven through the liner to expand it to hold it in place, and to size the interior diameter. It works surprisingly well. I followed the advice of this American gentleman on how to install them (caution - robust language).

https://www.youtube.com/watch?v=k3MezVMZ2hg

[englishmaninwales]

If you are considering replacement valve guides look into fitting phosphor bronze liners.
Results in much less valve seat work.

Any info please on typical costs for fitting PB valve guide liners?
Thanks
Malcolm

[alan.barker]

Hi Promotor,
To be honest i have not see this done BUT i worked in the Aero Space Industry and it was general practice.
You can gain 2 Thou (.002") easily.
The Alloy casting needs to be heated slowly and soaked to be sure it's 100% hot.
Guide to be inserted put in Liquide Nitrogen including assembly Tool/mandrel.
When assembling Alloy casting put on insulated Bench not direct on steel Bench. Someting around to stop cooling too fast.
We used this practice on Radar Systems.
Alan