....Cylinder head gasket continuation.....pictures now..

[berni29]

Hi All

Update after my head gasket failure.......I took the head to somewhere recommended by someone in a previous post on this subject, and they skimmed the head for me (?25). They said that the head itself was fine and needed no welding. They did chemically clean it though (?35). I specifically asked for it not to be blasted. The guides though are shot and they suggested inserts plus having the seats recut. There is really a lot of movement in most of them, especially the exhaust. Given that, how come the engine never smoked before? It used to start after a week with no puff at all. Two other things, they vacuum tested it (through the ports) and put the lack of vacuum down to the guides which makes sense, but does that matter? Also he laughed when I said that I would just lap the valves in and give it a go. Said something about a day of that not being enough and that it would never run. Why is that? I am a bit worried now!

I should post some pictures of the skimmed surface. It does have some curved marks on it. I took the head back and am trying to decide what to do.

Berni

[type26owner]

Berni,
The exhaust valve guide are suppose to have about twice the clearance of the intakes. If you plan on dropping the hammer then not following the recommended clearnances in the Workshop manual is foolish. Applying about one thou to the exhaust is just asking for it to sieze. The downside to using the Lotus specs are it will emit oil smoke without the stem seals. One of those Catch-22 situations I'm afraid!

My guess is it always smoked you just were not paying close attention is all. You can make it much worse by having the fuel vapors as blowby diluting the oil though. Changing the oil will help in that case.

What are the measured clearances? Lapping valves is thing of the past. I always replace the valves if they are pitted and regrind the seats. The valves are relatively inexpensive. One always checks the quality of the sealing surface with bluing paste.

[nebogipfel]

Berni, As Keith says there is quite a bit of movement on the exhaust valves when the guides are fairly healthy.

If you are replacing guides you need to have the seats lightly cut to the new guides. If, however, the valves were not burnt and on examination there is no serious pitting in the seats then there is no reason why you shouldn't lap them in quite successfully.

The curved marks you can see are artifacts from the cutter used to skim the head surface and are normal when a head is faced using that type of machine.

If your car ran, started and performed well prior to the gasket problem and didn't consume excessive oil (remembering it's a twink) then it doesn't suggest there were too many problems.

At the end of the day it's a decision only you can make. It's recondition by the book with no compromise (which will always be recommended by the engine reconditioners) or it's go with your gut, assess what you have and go that route.

[type26owner]

Oops, it only takes a small volume of coolant and water to drastically reduce the viscosity of the oil. This is bad since the oil film can shear much easier in the oil fed journal bearings when this happens. IIRC, 1% to 2% percent is all it takes to destroy a highly stressed race engine. That would certainly account for the sudden increase of oil smoke you noted.

Apparently another reason to not lap valves is some are specially coated on the seating surface. I don't know if the ones normally supplied for the twinkcam are or not. Saw this warning on the Lotus Cortina website just the other day as a footnote reference.

[berni29]

Hi

Thank you for the advice. I feel better about the play in the guides now. I think that I will have a go at lapping them in and putting back together. Do you know of a test for the valve springs, or at ?25 is it worth just replacing them?

I had not thought too much about replacing the engine oil, but I guess if there is possible water contamination that I will have to. Now that I know that the engine is a bit (or even very) worn I wonder if it is worth the expense of Mobil 1 again. Not that I want to open up that can of worms in this thread!!

On the smoke front, I lived with a +2 that smoked on startup for years so I am pretty keen on that sort of thing.

Thanks again

Berni

[type26owner]

Without one of these you're lost. Every serious engine builder has one. http://www.precisionmeasure.com/valve6.htm
If the springs have 50K miles or more on them I'd toss new ones in there. You have to roll those dice on the possibility of having to pull the head again is all. With experience a head gasket replacement is four hours of labor tops from start to finish.

Do you have a set of the special dowel pins to align the headgasket? Plunking the head down onto the headgasket requires two persons (one does most of the lifting) working together to do that one task. It only takes five minutes to complete that step though.

[berni29]

Hi

Sometimes a manufacturers claim can be taken with a pinch of salt, but I can certainly believe it of that device. I aspire to a workshop where such a thing would not look out of place!

Looks like a new set of springs for me!

Berni

[nebogipfel]

Berni, Never risk re-using oil when you have taken the head off. Some contamination must occur.

I appreciate what you say about oils and wouldn't wish to open the debate but FWIW I have always been of the opinion that a reasonable quality oil changed regularly is the way to go. I accept the claimed properties of modern oils but regular changes not only remove fluid contaminants but also the inevitable particles (and bigger lumps!) of one type or another which will accumulate. If you pay a premium for the latest hyper mega synthetic you are much less inclined to throw it away regularly!

I go for good old Duckhams 20/50 (cheap as chips even at the local motor factor) and change it regularly.

[type26owner]

On average my Elan costs me about 25 cents per mile to keep it in tiptop shape. It's a tremendous bargain when compared to the wife's 97 Corvette which commited suicide recently and when I added up the cost is came to a staggering $2 per mile! It sounds like you guys are spending a lot less then 25 cents...

[berni29]

Hi

Here in the UK there is a motoring questions and answers section in the Sunday Times, and the journo who does it used to always say to use a good quality ordinary oil and change very regularly. I think he advocated every 3,000 miles.

Keith must do a fair few miles which is good. Get the average cost per mile down! My current car has a LOT of catching up to do!

Berni

[M100]

Berni, can't you measure the relevant diameters and determine exactly what clearances you have?

The surface on the head ought to feel flat to the fingernail, you might see some marks from the cutter but no grooves. Heads and blocks I get machined locally come back with an almost mirror like finish, I commented on it the other month and they said their newer machine tooling would be even better.

Do you have a set of the special dowel pins to align the headgasket? Plunking the head down onto the headgasket requires two persons (one does most of the lifting) working together to do that one task. It only takes five minutes to complete that step though.

Keith you mentioned this before and sometime later the penny finally dropped as to what you mean. The "dowels" are usually just old head bolts with their heads cut off and a slot cut in their tops.

I've never heard of any prohibition on lapping before,even on very modern engines, have you got a link for that info? Even with newly cut seats and valves chances are they will leak without some lapping even though theoretically they shouldn't.

[type26owner]

Martin,
If you look in the fat Lotus Workshop Manual in the engine section they show the dowel pins. The headbolts will not do it. You're screwed if you do don't get the gasket in there perfectly centered on the bores. The compression ring of the headgasket can get hit by the piston. The gasket has two diagonally opposed headbolt clearance holes which just fit the dowel pins, all the other holes are oversized. Paying attention to the minute details is crucial to getting the headgasket leaktight. The aluminum head to a cast iron block thermal coefficient mismatch is huge. Reality is the head grows the better part of 1mm longer than the block when the engine heats up.

There are so many Cortina websites! I have to remember what I was searching for and ended up there unexpectedly.

Valves leaking a little is not that important on the timescale the combustion cycle happens. The exhaust valves need to shed some of the heat like at full power down a straightaway or they will glow and burn up by oxidizing.

[ppnelan]

Martin,

My Elan Workshop Manual says to make the 'dowels' from old head bolts with the tops cut off too - perhaps 'serious engine builders' use something a bit more special...?!

Matthew

[type26owner]

Yeah, if you want to make it about ten times harder use cutoff headbolts. Oh yeah, the guy holding up the head in that case has to be Superman too. They have to be screwed in after the head is gyrated around to clear the chain guide sticking out of the timing chain cover and not damage the gasket. Good luck!

Actually if the shank diameter below the head is a just fit in the clearance holes in the head and long enough then they would work okay as a dowel pin. Just stick them in there upside down so the threads are sticking out the topside of the head. Don't try to screw them into place in other words. There is a 1/4" deep counterbore pocket in the engine block threaded holes to accept a dowel pin. The aluminum plastically flows under the headbolt washers so you must ream that material out so the dowel pins will pass through.

[type26owner]

Berni,
Here's the best example of a surface finish comparator guage I could find. If you run the cursor over each segment a slightly bigger closeup picture pops up in the window below and to the right.
http://tinylinks.net/1806