Moss Motors, Ltd

It's a long story how I got myself in a position to need this information and why the motor has only one side of the timing mark.. My problem is timing my '48 Prefect flathead without a proper timing mark. More specifically, if I can find TDC then I can fabricate a timing mark and future timing will be much easier.

Thanks for any ideas short of remove the head.

Bayless

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

Bayless,

I can help you find absolutely perfect top dead center on your engine. First I will need you to answer one question for me. Do the spark plugs sit directly over the pistons? In other words, are they vertically situated in the head? It's not what you think. I'm not just going to tell you to stick a straw in the hole and rotate the engine until you think you've found the highest position. That would, for reasons I'll explain after your answers, be rather inaccurate. Looking forward to your answer.

 

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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

Thanks for the quick response Bill. No, unfortunately the spark plugs are over the squish area sort of between the valves.

 

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

enfop,

Nuts! We were going to use the elegant and extremely accurate piston stop method. Give me a few hours. I'll come up with another way. By the way, which half of the combination of marks do you have?

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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

Finding TDC shouldn't be too hard. First you'll need a degree wheel and some type of pointer. This might be a problem if the engine is in the car, if so then you'll have to be a little less precise but you should still be able to get close. Remove the plugs and make up a piston stop from an old spark plug. I've done this by breaking out the ceramic insulator and drilling and taping the plug body for an appropriate sized bolt. Raise the piston on the number one cylinder to nearly the top, install the piston stop and adjust the bolt until it hits the piston, then lock it in position. Mark the front pully or damper at this point and then carefully turn the engine backwards until the piston hits the stop again. Mark this point. One half way between these two points is TDC. If you're using a degree wheel, then remove the piston stop, rotate the crank to where the calculated TDC lines up with the pointer and mark your damper. If you don't have the degree wheel, then measure between the two marks and mark the center. You should be close enough to be able to set the timing and tune that Prefect.

To know where the firing point is for number one, just cover the plug hole with your thumb and rotate the engine until the pressue builds on the compression stroke, the set at the TDC mark you made earlier. You should be very close to a good point for an initial static timing point.

Sorry, didn't read motorbills answer and your response fully. The piston stop will have to be somewhat different if the plug isn't over part of the piston. I'm a little surprised that it's not, as most of the flatheads I've worked on needed the clearance over the valves and moved the plug sort of in between the bore center and the valves, but usually over the edge of the piston where you  could get a stop to register.

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'73 Midget (V6)
'59 MGA (I6) under construction
'73 Lotus Europa
'52 MG TD kit car body project.
'98 Jag XK8

"There is a fine line between a hobby and mental illness"

My '48 Prefect has a '58 motor with the timing cover from the '48 in order to use the original motor mount system. The '48 used a timing pin in the cover to a dimple in the timing gear. The '58 has a mark on the pulley (harmonic damper) and matching indicator on the cover. I failed to provide for the indicator on the cover when making the swap. So I have the pulley mark and not the indicator.

It has been a while since I had the head off but I am sure the plugs are over the block and not even partly over the pistons. I'm not certain but it may be possible to stick a wire through a hole and touch a piston. I wonder how accurate that might be though.

Bill, I do have it timed pretty well now by the T&E method. Got it close enough to start then test drove, top gear at fairly low speed and accelerate fairly hard. Advance until pinging starts then back off until it stops. BTW, I have an original owner's manual and that is the recommended method. Well, it does say to start with the timing pin and not my "best guess."

If there is anything else I can answer, I'll try.

 

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

I went back and took a look at your photos, and one shows the top of the engine pretty well. You are correct about the spark plug placement. I've never seen one with the plug that far over the valves. You might be able to find TDC by using a manometer and working off the alcohol level as the piston moves from compression to the power stroke and starts drawing vacuum but you'd still have an area where the change wasn't sufficient to show any reading on the tube and have to guess a bit anyway. Sounds like the tune by ear method is about the only choice for this one.

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'73 Midget (V6)
'59 MGA (I6) under construction
'73 Lotus Europa
'52 MG TD kit car body project.
'98 Jag XK8

"There is a fine line between a hobby and mental illness"

Ok lets see if this one (idea) can grow feathers and fly. My compretion tester will hook to a air line so my thought is to find the closed valve stroke then use air to fully push the piston to the bottom (180 out). Then by laying a srait edge from the mark across the center of the crank to the other side would be TDC. I would use low air , 20-30 psi ,and have the oil filler cap off just in case of blow by. Does this sound workable?  

In theory it might work. I'm afraid though that with the piston right at the bottom, a movement of several degrees on the crank would make an all but imperceptible vertical movement of the piston. That's probably pretty much like Bill suggested at the top. Just a very small error in finding the exact top or bottom could lead to a several degree error at the crankshaft.

 

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

enfo,

Absolutely. I'm still working on it though, and I bet I can come up with a true mechanical method. Since you have it running decently there is no reason to do it badly. Let's make a challenge of getting it right on the nostrils. By the way, do you have any camshaft timing information or profiling chart or perhaps a disc representation of the valve timing? That would make cake of it.

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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

No, sorry Bill, I sure don't have anything on the cam.

 

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

Hey Enfo,

I was reading back through all the posts on this thing and noticed you said that you had mixed and matched parts of two motors. Do you still have the timing cover from the motor that matches the damper pulley you have on this one? It seems like that plus some careful layout and measuring work might give you what you need, or is the admixture of the various parts such that this won't work? Just wondering and still cogitating....

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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

I've been working on some type of physical stop or indicator of the true piston position. How about a piece of welding rod or coat hanger bent so that it will feed down through the spark plug hole and reach over to the piston crown? Once you determine the length, a short piece could be welded or soldered to the other at the plug hole location to act as a pivot and the free end would be your pointer to determine when the pison movement had stopped. The longer the pointer, the more accurate the reading. It would probably have to have some sort of  bend at the end to reach down into the cylinder a bit, and be slightly curved if looked at from above to be able to feed the end past the tight constriction of the combustion chamber near the cylinder.  Sounds kind of like a bodge, but might get you the spot you want.

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'73 Midget (V6)
'59 MGA (I6) under construction
'73 Lotus Europa
'52 MG TD kit car body project.
'98 Jag XK8

"There is a fine line between a hobby and mental illness"

No, I don't have that either although your idea would have easily worked. I traded engines many years ago and had to give the boneyard operator a complete unit. To make things fit, I kept the old oil pump and front cover and replaced them on the old engine with those from the newer one. Man, if only foresight were half as good as hindsight. The really bad thing is, I had the head off in '98 to decarbon and relap the valves. Of course, I forgot to make a timing mark that time too. Hey Bill, thanks a lot for you interest and efforts. Meanwhile, if any more ideas come, please pass along.

It looks like Bill Y. was typing at the same time I was. It sounds like your idea may have some possibilities but also like it would be pretty hard to read it accurately. If I understood right, you are looking for the actual top rather than the more traditional way of coming up from both directions to a stop then centering between the two. Is that right? If so, it would take a really sensitive measuring device and the test rod would probably need to be quite rigid.

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

Yes, I was thinking actual TDC, but now that you mention it you might be able to get it bent long enough to be a physical stop between the piston and the head and use the other method. This would work if the head surface is relatively flat in that area and the pistons are flat also so any movement across the head or piston wouldn't alter the reading.

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'73 Midget (V6)
'59 MGA (I6) under construction
'73 Lotus Europa
'52 MG TD kit car body project.
'98 Jag XK8

"There is a fine line between a hobby and mental illness"