'73 TCS camshaft timing

[jbcollier]

Yes there is overlap at TDC when transitioning from the exhaust stroke to the intake stroke.  The exhaust valve stays open past TDC as the "inertia" of the exhaust gases flowing out the exhaust port continues to "evacuate" the cylinder.  The intake valve opens before TDC to take advantage of this partial "vacuum" created in the cylinder by the exhaust gases rushing out.  This is all simplified as it is a very complex system of pipe lengths, pressure waves, etc.

You do not calculate the overlap by subtracting how long one valve is open from the other as they are largely open at completely different times.

Unfortunately, however, the two valves will hit if they are both wide open, and hit any piston that is at TDC.  This is why it is critical to have the cams in position before placing the head on the block.  Having to turn the cams more than a few degrees usually means trouble.  Wide open valves also extend past the head surface so you can, if the cams are in, bend a valve by simply placing the head down. 

Have you done a compression test yet?

[EuropaTC]

it's a 4-cycle engine. Suck, squeeze, bang, blow

 

I just love that description.....    and so apt for a Lotus engine

Brian

[hey_kramer]

Problem 1
So it finally runs!! ...but not well. Timed valves to -26 BTDC IO and +26 ATDC EC, just like the manual. Ignition seems to be happiest firing between 5-10 BTDC, but don't ask it to idle for more than 10 seconds, even at full choke. Runs smoothly between 2000-4000rpm. Below 1500 and it starts to shake and sputter. Below 1200 and the shaking gets really bad. Dies when below 1000 for longer than a few seconds. Have not done a formal compression test, but I can tell you that when manually rotating the engine by turning a rear wheel it becomes difficult to rotate the wheel when a chamber is in its compression stroke.

Problem 2
The brand new head gasket and cam cover gasket I bought from R.D. leak very badly. For the head gasket I strongly suspect the sealant is to blame. For the cam cover an apparent warped or mis-shapen face of either the cam block or cover is to blame for the gasket leaks. With the cam cover nuts torqued to spec I can FREELY slide the gasket back and forth under the cam cover in the spots where it's leaking. Either the face of the cam block is warped or the cover is. The cover leak should be remedied with a better bead of sealant, but I'm going to have to remove the whole block again to fix the head gasket leak...

[BDA]

That's too bad about your gaskets. While you have it apart (again), I'd make sure that the head and the deck are flat before putting it back together. I assume you used a copper "asbestos" gasket. I used those in the dark ages on my MG F-Production racing Midget. I don't remember using any sealant but I could be wrong - that was a LONG time ago!

A compression test and a leakdown test before you tear the engine apart would be useful. You might have a carburetor problems.

[hey_kramer]

I assume you used a copper "asbestos" gasket. I used those in the dark ages on my MG F-Production racing Midget. I don't remember using any sealant but I could be wrong - that was a LONG time ago!

The old gasket I removed (installed in 91) was copper and asbestos, but I used a new style composite gasket which Ray at R.D. trusts. That's why I am initially blaming the sealant I chose. When I took off the original gasket there was no sealant used on it, but this new gasket recommended a thin sealant layer. Perhaps I didn't get it installed fast enough and it dried out in some places.

A compression test and a leakdown test before you tear the engine apart would be useful. You might have a carburetor problems.

The Zenith carb for the #1/#2 chambers definitely needs adjusting. The plugs in #1/#2 always foul quickly. However, the engine ran very smoothly before the first teardown last month, and I didn't do anything to the carbs except set them on the workbench, so I don't attribute anything major to the carbs that would cause the shaking and non-idling at lower RPMs.

[jbcollier]

Check the carb diaphragms

[hey_kramer]

Check the carb diaphragms

Thanks. Both diaphragms look great. Very flexible and seal looks good. Carb oil is proper level and needles move up and down with ease.

[BDA]

What do #1 and #2 foul with? Oil? If so, assuming you're using the correct heat range, you probably have a problem either with rings or valve guide/seal or some combination. If it's gas, you'll have to look at your carb(s) again. Make sure the butterflies are synchronized and the carbs have been balanced with a Uni-Syn or something similar.

[hey_kramer]

What do #1 and #2 foul with? Oil? If so, assuming you're using the correct heat range, you probably have a problem either with rings or valve guide/seal or some combination. If it's gas, you'll have to look at your carb(s) again. Make sure the butterflies are synchronized and the carbs have been balanced with a Uni-Syn or something similar.

#1 and #2 both foul with oil immediately upon engine start. They've fouled for a number of years but it wasn't something my father tried to fix because the engine ran fairly smoothly regardless, so he didn't give it too much concern and just lived with it.

[BDA]

Hmmm... Their being next to each other and the fact that you have a head gasket problem might imply that you're leaking oil into #1 & 2 from an oil passage up to the head. I'm a little confused. A truly fouled plug will not fire reliably. Could it be that they are getting fouled worse than they used to? A leakdown test and a compression test may point you to the problem. Do you have new valve seals? Are your valve guides in good shape? Rings?

[EuropaTC]

The TC doesn't have any valve seals, it just hopes the machined fit between valve stem & guide and the cam bucket in the head is good enough to give a bit of lubrication and minimise oil loss.  From my experience if it's worn valve guides then you get clouds of smoke well before the plugs start to foul up and affect running, so your conscience (and looks from other motorists) get to you long before the plugs start oiling.

So if they really are fouling with oil and not just an over-rich mixture then I'm with you on the head gasket or maybe bore problem and a compression test sounds like the best move. From the comments so far with clearances there sounds to be something wrong in the head assembly so after a quick compression test I think I'd be pulling it apart again.

Brian

[hey_kramer]

I'm a little confused. A truly fouled plug will not fire reliably. Could it be that they are getting fouled worse than they used to?

They are getting fouled just as they did in the past. I should perhaps call them "partly" fouled, because (before the tear down) the engine ran smoothly but smoked a little bit at low RPMs.

Many months before my tear down to replace the head gasket, I installed an electronic ignition, new plugs and wires. My father rarely serviced the vehicle, rarely drove it, and the last time he had replaced the plugs was nearly 10 years ago. But keep in mind he had ONLY driven about 3000mi (4800km) in 10 years on those plugs. Original plug #4 was covered in dry soot; #3 was light brown just as it should be; #2 & #1 were identical, both coated with about 0.5mm of burned oil.

I installed new Champion plugs and found that the new plugs resembled the old plugs after only about 20 miles of use! #1/#2 oiled; #3 great; #4 dry soot. Seeing that my brand new plugs had already been oiled is what finally pushed me to replace the head gasket. When I exposed the chambers I was very surprised to see that the #1 and #2 chambers looked pretty good. I thought for sure they were going to be nasty. After installing the new head gasket, #1/#2 still oil just as bad as before. However, the new gasket leaks in multiple places on the outside of the block, so I can assume it is leaking into the combustion chamber as well, possibly causing the oiled #1/#2. Old, worn head gasket = oily plugs. New head gasket installed improperly = oil plugs. I shall find out in the coming weeks.

[jbcollier]

Almost never is a head gasket the reason oil is getting into a cylinder.  Some engines suffer from oil leaking out like the Alfa fours but not the Lotus engine -- though there are plenty of places they do like to leak oil.  The reason #1 & #2 looked good is that the oil is "washing" the cylinders clean.  This most likely means that your oil control rings are toast or mis-installed.

Reading through this thread, it seems you do not have any experience working on engines.  May I suggest you get some help?  Please also do that compression test so frequently mentioned as there may be a bent valve or two

[hey_kramer]

Reading through this thread, it seems you do not have any experience working on engines.  May I suggest you get some help?  Please also do that compression test so frequently mentioned as there may be a bent valve or two

Much thanks for the advice. You're exactly right, unfortunately I don't have any experience working on engines, but sadly my finances will not allow me to spend the large lump of money required to tow it and have a professional mechanic fix the issues. But what I do have is ample time to study the manual(s), forums and other internet sources, and the ability to consult my two uncles who originally rebuilt the engine 22 years ago with my father and really ARE genuine mechanics (the car is over 1000 miles away from them now, though). I'm absolutely going to go buy a compression tester and research the proper procedure to measure. I'm afraid of what it'll reveal! I'm fairly certain a valve is not bent, as I painstakingly researched beforehand the proper way to remove and handle the valve block so as to ensure safety of the fragile valves...but you never know. Will be a few weeks before I can resume work on it. Thanks once again.

[jbcollier]

No need for professionals but anyone with some familiarity with twin cam engines would help.  If they rebuilt the engine and it's been oiling #1 & #2 plugs ever since, it is possible they put the oil control rings in upside-down.  I have seen that happen quite a few times.  You can usually borrow/rent tools from some auto parts stores so there is no need to buy a tool that will see limited future use.

Also, when you remove the head, the chain falls off the crank sprocket and when you go to put it back on, the auxiliary shaft (which drives the distributer) will not be in the same position: just another thing to check.