Oily Twincam

[Ramsden]

Following the unfortunate collapse of the timing chain tensioner resulting in a jumping chain and attendant piston valve collision, the head of my big valve twincam has been rebuilt. This included including the replacement of all valves, guides, and seats(unleaded conv.), timing chain tensioner and, naturally, all related seals & gaskets.

Since then I have suffered from an oil burn problem that was not present before rebuild.

On starting the car, it runs cleanly. Once up to temperature, however, a puff of blueish smoke will emerge on pulling off from a standstill. I'm not sure whether this continues to happen after pulling away as the air stream may be carrying the smoke away.

The problem is particularly evident when the car is stationary and is left idling for a while, when blueish smoke segins to emerge from the exhaust in increasing amounts.

Does anyone have any experience of these symptoms or have suggestions as to the source of the oil and its means of entry into the combustion chamber.

As the head rebuild was arranged under duress by the garage from which I bought the car and partly paid for by them (they having okayed the timing mechanism 1 week before its collapse) problems with the head cannot be be wholly ruled out.

Many thanks

Simon

[JACKJABBA]

Sounds like the valve guides. My head has also been rebuilt, and it gives a little puff of blue when giving it a foot full. Seem to have read that they usualy do this. If its smoking a lot then I would get it back off and have it checked.

[JACKJABBA]

Sorry , but I am talking out of the wrong end. Smoke on acceleration is rings, smoke on deceleration is valve guides. :unsure:

[markb]

Simon,
How much are you using? If you are using fully synthetic oils there will be a tendency to burn more due to the viscosity and the absence of valve stem seals.

Mark

[type26owner]

5-08110 Teflon Valve Seal 8mm (5/16) X 10.5mm Short $2.50
www.aptfast.com
Shorten the tapered keepers by .05" and these seals just fit the standard lift cams okay. The inner raised flange of the steel spring seat washer must be machined away to pass over the installed seal too. Lasts for 50K miles I'm finding.

On acceleration it will pull oil in from the brand new exhaust guides because of the venturi effect and on deceleration it pulls oil in from the intake guides from the vacuum because of the Lotus Manual prescribed clearances. Every twincam I've ever seen has a telltale built-up carbon soot track from the exhaust guide into the exhaust port, look for it next time. Just remove the exhaust manifold and shine a flashlight into the port to do an insitu examination. This is poorly understood and WELL documented. Besides there are few current engines that don't have valve guide seals. The State of California encourages it's citizens to snitch on their neighbor's oil smoking cars now. What a pain.
Keith

[JACKJABBA]

Do you get a puff of smoke when you start the engine?, if not and then it only starts to smoke when getting hot, and keeps getting worse. I would redo the head gasket. Mine started to smoke when warming up, the warmer it got the more smoke came. I stopped the engine and left it for 15 minutes. restarted and it was fine. Changed the almost new head gasket and now I get a small puff of blue smoke when starting up, then nothing unless realy giving it some.

[dmreeceuk]

On the subject of smoke, I also get a puff of smoke on acceleration but only when really flooring it. And then only if ive been off the throttle before hand. Is this normal or signs of a rebuild.

It doenst use much oil.

I really dont know when u need a rebuild and as its an expensive job I would like to extend the time till I really need it.!!


Dave
1970S4

[types26/36]

Simon,
In theory if the head was rebuilt as you say (or were told) the problem should not be there but in the real word............did they do everything!
You do not mention if there was any piston damage when valves hit pistons.
Most T/cams do give a puff of smoke when starting up due to no valve seals in standard form but does this happen under acceleration or deceleration?
Sometimes by removing & installing a cyl. head it can disturb the piston to cylinder seal, usually with a "high milage" engine and can cause problems.
If no work was done on the pistons was the carbon scraped off the top of them? it is usual to leave a ring of carbon around the edge so the seal (piston to bore) is not disturbed.
Another point to check, is it useing engine oil? brake fluid pulled through a faulty brake servo will also cause smoke but you would see your b/fluid going down
(just a thought)
Brian.

[pistonbroke]

for what it is worth i have had this problem here goes ,when the old guides were removed and new ones fitted the engine builder scored the head where the valve guides fit ( between the outside of the guide and the head ) causing oil to be pulled down past the outside of the guide ,may not happen on all the cylinders but it only takes one guide and can be an absolute pain to find ,we had 2 engine strip downs to find it ,sounds like the same thing ,worth a look

[steve]

thats funny i had the same problem , mr broke

[type26owner]

It's simple to remove the guides and do no damage at all. From the port side relieve most of the guides' wall thickness with a 7/16" diameter counterbore with a 5/16" dia pilot. The removable pilots are fragile and cheap so buy at least four to do one head. Counterbore to within 1/4"of the farend of the guide. Clean the carbon deposits away, spray some lube on the guide, insert a pin into the counterbored end and tap them out. They come free with very little effort and will not drag any aluminum with them. mcmaaster.com lists the counterbore and pilots.
Keith

Steve, it is easy if you know the tricks of the trade. BTDT. Just because someone is suppose to be an expert doesn't make it so. My buddy just had his Maserati heads destroyed by an expert who didn't know how to remove valve guides either. He's distraught knowing that the idiot then proceeded without asking and knurled the guides OD and when that didn't work he just glued them into the heads. Only when the owner inspected the heads and asked what had happened did this idiot confess. Just another example why it's better to do it yourself.

[steve]

only if it was that easy all the time you make it sound so simple
type 26 ................ i am in the trade

worth a look at the guides though its so easy to score the head depending on how they are removed ,some poeple just bake the head in an oven then press them out or just simply drift them out ,and its so easy for the guide to pick up on the head ! the problem is if someone has done the headwork for you ,you will have to look at every angle ,take nothing for granted ,still at the end of the day people can offer addvice all day long ,if i was in your postition i would take it to someone who knows about these engines and explaine to them your problems and let them look at it for you ,you can waste a lot of time and money with problems like this , hope this helps steve ...........! <_< just remebered summat ,if its doing it on tickover and on very light throttle it would be trying to pull oil down anyway because your butterflys are not open on your carbs and with your inlet valve's open and piston on the down stroke it has to pull air (and maybe oil ) from somewhere ( low manifold pressure ),you can only get so much mixture etc on tickover and light throttle

[Ramsden]

Thanks all for the heaps of useful advice.

Looks like the first step is to remove the head and get it inspected by someone who knows what they are talking about. If that can be eliminated from the equasion then I'll move on to the pistons (incidentally, not damaged).

Have been thinking of using PMSC as they are close to my folks place on worcestershire. Does anyone have any comments/experiences of using them?

Simon

[elansprint71]

Blue smoke usually but not always means that oil is passing from the sump past the rings and being burnt off, if oil is passing the valve guides on the over-run you will see white smoke when the throttle is opened. I'm not sure how this advice is of any help!

How bad was the meeting of valves and pistons? Did the engine stop immediately, i.e. you kicked out the clutch, or was it driven round by the wheels for a while until you stopped?

Either way, it looks like the "rebuild" was less than complete and it might cost a fair amount for a second rebuild by QED, or someone. Any help form your insurers in the form of DAS uninsured loss?

Best of luck,

Pete