Moss Motors, Ltd

Yes, I think a piston position indicator, angled downward, which would show that the piston had reached a certain point when approached from either direction might work. There are two difficulties to overcome. One would be to build a pivot device accurate enough to prevent any deflection whatsoever, and the other would be to make the moment arms stiff enough for the same reason and to indicate against a dial gauge. At this point, I would think the trouble you'd go through would be greater than removing the relatively simple cylinder head and using the piston stop method with a nice stout piece of angle iron across the cylinder. That's how I do it when I'm setting up camshaft timing with the head off the engine, as I build it.

Really, would removing the head be all that much difficulty? I won't assume anything here. And, I'll admit I kind of like the challenge of trying to find a way around it. But you know, challenges are only good up to a point. If someone challenges you to make a hole in a brick wall within ten minutes, that might be cool. But if, at the last moment, they add that the only tool you can use is your head, well the challenge turns into a fool's errand, or worse... Still, I'm thinking about this one. What does that say about me?...

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

All right guys. It,s me again with another off the wall siggestion. ...I vaguely remember reading somewhere about a t.d.c. locator which was a whistle you would screw into the spark plug hole.  As the piston rose it made the whistle blow, at the top it stopped, onthe way back down it would start again.  Come to think about it a compression tester would do the same thing. Having said that it sounds like the owner,s manual suggestion of performance testing it offers the best solution in tuning it.  After  finding the best setting, mark it as a baseline for the future.

Sometimes the flywheel will have timing marks stamped into the edge that are readable through an access plate. This is often forgotten.

We were kind of looking for dead nuts accurate timing here. The old whistle trick gives you a pretty good idea, But as I'm sure you know, the actual vertical, and therefore air displacing, movement of the piston during that last several degrees of crankshaft rotation either side of TDC is so slight that it would probably preclude really great precision. I still vote for the "Off with 'er head!" approach.

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

If both timing covers are the same shape with the exception of one having the timing mark and  you still have the original or know somebody who does , why not make a clay impression of it and transfer it over using some points of reference off each piece to properly locate it?

 Also, the manometer idea could be made to be extremely accurate by decreasing the diameter of the tube in which the liquid is rising or falling. It would take a minute amount of movement of the relatively large surface area of the piston to get the fluid to move a long distance in a very thin tube. My main concern with this system would be in making a mess squirting water all over the place.  You'd want to get as close to tdc as possible before hooking the thing up.  It's true that the piston "parks" itself at the top and bottom of its travel but----- Wait a minute! a better idea that will work!!! Purposely set the piston at an area known to be OFF TDC , say ahead around 10-15degrees.  Mark location on timing cover. Hook up manometer. Take reading. Rotate crank normally and slowly while watching manometer rise to top at tdc and then start falling again. When it falls back to its starting point mark location again. It will be the exact same distance past tdc as you were before tdc, same idea as crank stop method! The mid-point  between the two marks will be TDC!
 

 

 

Icjutila,

The original timing cover, if I have read correctly, is long gone. The manometer piston off TDC rising and falling idea is intriguing. It's sort of a hydraulic variation on the piston stop method. However, I think I see a problem. In the real world liquid or air will always be escaping past the imperfect seal formed by the piston, the rings, and the cylinder wall. There would be a diminished amount of liquid after the process started. You would have to be able to calculate that loss and factor it into the result. MY Brain Hurts! Theoretically speaking, I love the idea. Practically speaking, I think it comes up with the same shortages as all the other ones we've thought up, just expressed through a different medium. This problem is going to ultimately be solved with a method totally outside the box....probably by a 12 year old.!

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Im thinking low pressure= low leakage. After typing the idea my thoughts were more about the volume being displaced and the ability of the manometer to handle it. If you could hook up something that could handle the volume displaced from say 90 degrees before tdc or more and then go through the motions described the percentage of volume displaced compared to the leakage past would be minimized. My understanding is that a manometer is just a column of water being displaced by vacuum or pressure. If the column of water is low in volume the pressure and therefore the leakage will be minimal.  You could maybe put a dollope of 30W down the sparkplug hole to minimize leakdown. If you have leakage past the valves at such a low pressure you,ve got other problems besides were the "H" tdc is. At that point we would go to plan "B" . Take off the head, regrind the valves, and find tdc while the head is off as you suggested!

You could test this system for accuracy on another engine where you already know where tdc is and compare the method's results to actual.

This is fun! 

Icj,

You know, I'm beginning to see possibilities here. The greater the crankshaft travel both before and after the "apogee", or TDC, the more accurate the whole thing would be. That would, of course, be limited by the valve timing. Perhaps the pushrods can be removed. It depends on the mechanical design of this engine. They could at least be backed off considerably. Then again, for accuracy, the manometer tube should be relatively small in diameter, meaning you'd need a ladder to read it!! I bet the original poster, enfoprefect, thinks we're both nuts by now and has given up on the whole idea...

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

The pistons are flat and are very close if not exactly level with the block top at TDC. I don't remember the combustion chamber shape so well except that it is fairly regular. That is, no funny deep or shallow spots. If I can make a rigid enough probe and get it in place that still might work. I'd have to evaluate though as breaking a piece of anything of inside a cylinder would not be a good thing.

 

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Bayless
Never express yourself more clearly than you can think
'48 Prefect
'67 Sprite (project)

Motorbill-

Finding exact tdc on ANY engine is almost like trying to figure out how many angels fit on the head of a pin. It all comes down to a matter of degree of accuracy. The thing you should be looking for in the real world is a functional approximation. That's why I like the shop manual's approach of setting the timing based on a road  test. I've got a 69 Mustang with an harmonic balancer on the front of it that has the timing marks on it on it's outside ring. The part of the pully that attaches to the crank and the outer ring of the balancer are separated by a rubber doughnut that dampens crankshaft vibration. Over time , the outer ring slips on the inner ring making the timing marks nothing more than wishfull thinking as to where tdc is. TDC is an almost arbitrary point that we use as a starting point to set other things. Everything is relative to TDC but if you used the correct figures in your setting you could make all your adjustments relative to BDC if you wanted to.

Anyway, it sure would  be fun to all put on white lab coats and grab some clip-boards and magnifying glasses, grab the garden hose and a ladder and looking as serious as possible try this thing out!

Anyone who thinks I'm nuts can get in line.... It forms to the right! 

Sure,

I certainly agree that it's a relative thing. What good is pinpoint accuracy in timing if the fuel you get from tank to tank and the temperature,humidity, and barometric pressure vary all the time? That said, I just like accuracy for its own sake, and because it makes for a really good jumping off point into the world of guessing. If we wanted automatic perfection we'd all be filling our antique cars with knock sensors, ECUs, auto timing devices, and all that other wonderful stuff that frankly bores me to tears. It's fascinating in principle and in execution, but it takes all the art out of the thing for me. Maybe not for others. That simply reveals my age. That's OK. I can get over it. I love learning new things. I'm always reading about the frontiers of science. When I find someone else who will discuss astrophysics or sub atomic mechanics I am in seventh heaven. But when it comes to practical application I like carburetters and pure mechanicality. That's just who I am. It takes all kinds...

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon

Maybe Im coming across as acidic in my postings. Im just failing miserably at being funny. I think everyone's postings and points of view are great and I truly enjoy and respect each and every one. I seriously took a long time getting to sleep last night thinking about  TDC and all its ramifications. Maybe this is some sort of support group for people with BCD (British Car Disease) and nobody told me. Well, I fit right in.

Although it is yet to yield viable results, I am really glad I started this thread. It really amazes me some of the ideas you guys have come up with. Some are really pretty ingenious and some might even work. Unfortunately, as Motorbill hinted, those that might actually work would probably be more effort than the straight forward solution of "pull the head." Well, if it comes to that (one of these days) I do have a couple of spare NOS head gaskets. Parts for this bady are really hard to find in this country though. Most of what I have found comes from Australia and one guy in CA. It is an interesting challenge though and, who can say, one of you guys just may hit on the ideal solution.

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Bayless
Never express yourself more clearly than you can think
'48 Prefect
'67 Sprite (project)

Just had another idea expanding on the manometer idea starting somewhat before and rotating through TDC until the level returns to the starting point. Since we think the leakage would make that inaccurate, how about doing that and marking the start and end angles. Then do the same thing rotating backward until the level is again equal and mark those angles. Would not the average of the two operations get pretty darn close since the leakage should be the same going both ways? I don't think I'll actually do it this way but since we now have our lab coats on it just seemed like another idea.

  

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Bayless
Never express yourself more clearly than you can think
'48 Prefect
'67 Sprite (project)

enfo,

I swear that just as I started reading your last post the same idea struck me! I'd like to think I was psychic, but when I've mentioned that to folks they say," No, Bill, not psychic, psychotic. And there's a difference!"

Perhaps the mental stumbling around of three or four obsessed "individuals" has struck theoretic paydirt. The keywords in your post are "darn close". I've had fun. I'm going home and drink some television and watch a beer...

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Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon