Head-off job looming; distilled wisdom sought

[hatman]

Progress to date:-

Head removed and skimmed (8 thou). New valves and springs acquired. However, it is now apparent that exhaust valve guide on No 1 cylinder is shot (new valve waggles about in it like a ten-year-old's tooth). Curiously, this is not the cylinder that went awol before the start of this saga - that was No 4 which, although compression testing at 180 odd did show a fair bit of pitting on the valve seat.

I do like the sound of the modern high tech material valve guides that Rohan recommends but this gives rise to a few questions/doubts:-
1) I only intend having the exhaust guides done as the inlets seem OK - is this advisable or am I storing up future trouble?
2) Where would I acquire such exotic modern devices?
3) As the valve guides are being replaced should I (and indeed is it posssible) to incorporate guide seals rather than stay with the crude(?) un-sealed originals?
4) Anyone know of an Elan-savvy machine shop in the Surrey area to whom I could safely entrust the work?

[gjz30075]

Absolutely do all valve guides. The extra cost is really minimal to the whole job.

I don't think you can get seals on the valves. Technology has come a long way on the twinks but IIRC, seals isn't one of them.

[M100]

If you search the archives there are a few references to Keith fitting valve guide seals. As far as I recall he only fitted them on the inlet side though and it required some mods to the valve guides and possibly to the seals.

http://www.lotuselan.net/forums/viewtopic.php?t=1053

Pics at http://briefcase.yahoo.com/[email protected] in the directory "Twincam_Valve_Stem_Seal"

Most modern seals are metric sized but the OD of the valves is conveniently 0.3125" = approx 8mm. The OD of the guides is 0.5" = approx 12.7mm, a bit of machining of the valve guide OD at the top could get that down to say 12mm and an off the shelf seal here in to UK might work (height is apparently also critical)

Finding a suitable seal is the hard work. I might be calling into my engine rebuild shop in the next week or so. I'll pick their brains and see if I can turn anything up.

[steveww]

I agree have all the valve guides fitted. Any good machine shop should be able to do this work and supply bronze type guides. IMHO I would not bother with seals. The UK MOT only requires minimal smoke on old cars.

[rgh0]

Its certainly possible to fit seals but it takes careful and knowledgeable redesign and you are limited to a standard lift cam unless you do even more redesign work on the rest of the valve train. You can actually probably fit seals on an engine with up to around .41 or .42 lift cams, you just need to build a valve train that could handle a .5 lift cam and use the spare space for the seal.

Keiths descriptions of how he did it was sound and if you can find it in the archives I would use it as a reference in talking to a machine shop on what you want if you go down that route. Oil leakage is greatest down the inlet guides but leakage down both inlets and exhaust can be significant. Personally I dont believe guide seals are needed for the usage most twincams get these days if you build the engine right in the first place and build it with the guide clearances to the bottom end of the tolerance range with modern guide materials and run synthetic oil. You should get at least 50000 miles smoke free which is a lot of years for most Elans these days. Keith was doing a lot of miles and trying to build 100,000 mile engines which is why he wanted to use seals.

For good modern valve guides I would talk to someone like QED on what they use in their high performance engines. The Elan Factory here in Melbourne is another supplier as cost to ship would be relatively small. The Elan Factory actually gets its guides made in the UK so you may get a discount if you can get it supplied direct in the UK without them going to Australia and back. If buying guides separately from doing the fitting you need to remove the old guides first to check the bores in the head and then get suitable sized guides to fit the bores. A lot of heads these days have oversize outside diameter guides to fit larger bores in the head due to wear over the years as guides have been removed and refitted.

regards
Rohan

[john.p.clegg]

Or you could do like I did and make up a cutter that fits the top of the guides after fitting and cut a taper in the top to "scrape" any excess oil off the valve stem..............

John

[hatman]

Thanks everyone for your input - as always it's helpful, interesting, reassuring, thought-provoking and occasionally a wee bit controversial.

The job proceeds. Talked to my local machine shop, armed with your thoughts about guide-renewal and kindred matters - net result is that he's put 'K Line' bronze inserts into all the exhaust valve guides and one of the inlet guides, the other inlet guides being deemed well within book tolerances.

Tells me that replacing cast iron guides with bronze ones is no longer regarded as the way forward in view of the rapid wear rate of bronze; this reasonably recent 'K Line' insert technology apparently gives the best of both solutions and is, of course, easily renewable if wear does become an issue (although with the pampered, low-mileage lives that the majority of old Loti - mine included - now lead, that's unlikely to be of interest in my lifetime).

Any doubts about the servicability of these inserts are immediately put to rest by the knowledge that Steve, the machine-shop wiz, and his chums use them in the drag-racing Scoobies and the like that they squirt up and down the strip at Santa Pod. Good enough for me!

[steveww]

The K-Line thingies are what my machine shop used when I had the head done last year. So far so good Then the Elan only does about 3k miles a year.

While the head is off had you though about doing some porting and flow work on it?

[rgh0]

K line inserts are an interesting technology and have been around for a lot of years and sometimes work and sometimes dont. The problems relate to getting the right clearances when fitting and the fact that they do not appear to be a very good bronze alloy at least for use in a twin cam.

You need to machine the worn guides accurately to fit the inserts and then machine the inserts accurately to get the guide to valve stem clearances right. All this machining and fitting can lead to problems. The final surface finish, straightness and clearance of the valve stem to guide is critical in a twin cam and I have chased smoking problems in a number of engines of friends with K line inserts before finally fitting new guides to fix it.

Secondly the material appears to be a relatively soft and easily worn bronze that has limited life in the relatively short and highly load valve guides in an Elan.

All this does not mean they dont work just that it can present problems on occassions depending on the quality of the work.

For a road engine worth a try if wanting to save dollars but compared to a new good quality copper or bronze alloy guide not the path I personally would go down. With luck your machine shop guys know what they are doing and understand enough about twin cams to get it right.

Rohan