Head off again!

[chrishewett]

Well the head is coming off again today!
I am forced to do this to finally find out what is causing my poor compression test results.
The head was rebuilt at PNM about 4 years and 3000miles ago. It has always been noisey with a loud tapping until it warms up. It was skimmed at the time and I seem to remember that they only just had enough metal to do that.
It doesn't use much oil and there is no smoke even on start up.
As this will be the sixth time it has been off for one reason or another I am keen that it is right this time.
Any tips or advice would be very gratefully received. What type of head gasket? Should I use a sealant?
I have run a search of previous threads but some up to date input would be good.
Thanking you all in advance.
Chris

[steveww]

When I did the head on my S4 I got a replacement gasket from Sue Miller and used Wellseal when putting back together. RTV for the timing chest and cam cover. I used a stud extractor to pull the exhuast studs out before lifting the head, it makes it easier to clear the manifold.

So far so good, no leaks and even compression.

While the head is off why not do some porting and polishing?

[M100]

Check the head and the block for flatness with a straightedge and feeler gauges, for erosion where the sealing ring on the head gasket meets the head and the block and check the head hasn't gone soft though overheating leading to gasket imprinting.

The loud tapping isn't right. Maybe a worn cam follower sleeve?

[chrishewett]

The bad news is that two of the cylinders are scored ( the two with the bad compression, 2 & 4). So it looks like the bottom is coming out as well. Unfortunately it has already been bored to +60 so it will have to be relined.
I suspect the culprits are the carbs washing to much petrol in.
Hamish you are not alone!
Chris

[Hamish Coutts]

Sympathies Chris.

I seem to have solved my flooding problems with resetting the fuel pressure to 2 lbs/sqin. Car's going a lot better.
Hopefully, it didn't do too much damage.



Hamish.

[denicholls2]

I have no experience with same, but understand you can order them in multiple thicknesses to make up for space lost to skimming. They're alleged to be re-usable as well.

Sorry to hear about the bottom end, but it's hard to believe that fuel alone would cause a pair of scored cylinders, especially in 4k. If so, why not all four? I'd look carefully at the rings, specifically the vertical gap on the pistons.

[M100]

Chris, sorry to hear your bad news. Unless you are striving to keep the original engine number you might find a used block, maybe a 711M more economical than resleeving. QED want 400 quid for resleeving, then there is the cost of pistons on top.

I'm off to have a word with a place that might be able to do it *much* cheaper possibly on Friday.

[chrishewett]

I have been told that I can have it resleeved for about ?200, new pistons about ?300. After adding new shells, gaskets etc I don't expect to have much change out of ?1000. I don't yet know what work the head will need, reshimming at least, so that will be on top. I am taking it over to a twincam guy in Newark on saturday and I hope to have the full sp then. He comes very highly recommended and has been working on these engines for 30 years. However, any suggestions from you guys is always valuable.
Chris

[steveww]

Why new pistons as well?

If the block is being resleeved then surely you get it done to +60 to match your existing pistons? Of course check the pistons to make sure they are OK and if so fit new rings and reuse them.

You can save a lot of money by doing most of the work yourself. Of course you will have to have the machine work done by a shop but the strip down and build up you could DIY. You can certainly do the reshim yourself and it only costs a few quid for some shims.

[M100]

Resleeving and then boring out to +60 would be a bit of a waste, even if you could reuse the old pistons it hardly makes economic sense - it's just 100 quid or about three tanks of petrol for a set of new standard size pistons from Lotus, the cheapest oversize pistons are more than three times that.

[steveww]

Ah I did not realise that standard size pistons were so inexpensive. Must be about the only part for the Lotus that is

However they are still way cheaper than Porsche parts. I found an old receipt for some Porsche bits for my last toy, must never let the boss see it