Finding Top dead Centre

[horse]

Hi, just been trying to check the timing on my M38 and came across the old problem of the L head spark plug hole is not above the piston. I can get it close but not spot on. Some say they use a Wiggler wire which will show when the piston reaches the top. Does any body have a photo of this or measurements to make one as I would not want to get anything stuck inside !!
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1952 M38

[RonD2]

Hi Horse,
In all the posts I've seen in this forum I've never seen a photo or measurements for the infamous "wiggler".

Wes does a nice job describing it, and how to use it, in a handful of posts if you use the search button above on the word "wiggler".

I've never tried it myself, but from how it's described, I think I'd use a piece of solid copper wire about 6-8 inches long. And be very careful to remove it (or have a hand on it) every time the piston is more than an inch from the top.

Good luck!
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Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

[horse]

Hi Ron, thanks for the reply I will search as you said. The other way I was going to attach a ballon fixed into the front spark plug hole to find the compression stroke then watch it expand and contract ,then the distance between the two should be TDC, if you see what I mean.
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1952 M38

[RonD2]

Balloon is an interesting idea. Somewhat like a leak-down test? Do you think the piston would hold and move enough air in enough time to make a large enough change in the balloon to see it? Valves and rings would have to be in perfect condition and adjustment?

How about a graduated pipette with colored water?

Would an air pressure gauge work? I'd think it would need to be a lot more sensitive than a compression test gauge. Measure a few pounds instead of 100.
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Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

[horse]

Hi. Yes I have seen a description of putting a clear tube down into the sealed spark plug hole and the other end ito a jar of water. When it bubbles it is on compression and then going down it would start to suck the water. I have got a compression gauge on order so will see if you can see a noticeable difference.
I would just like an unit to show what is happening with the piston.
Wes did post using a Degree Wheel which I am still finding out about.
Will let you know how I get on at the weekend with the different methods.
Horse
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1952 M38

[RonD2]

I also thought that a slim enough fiber optic camera with an LED on the end would allow it to be seen. They get expensive the smaller they are.

Maybe a lot of work, but drop the oil pan and look at the piston from the other end?
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Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51

“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari

[wesk]

The assumption that you can find true top dead center by dividing the time piston spends around top in half is a NO. My basic rule of thumb is to make darn sure I have an accurate ignition timing mark setup on every engine I assemble BEFORE I put the head on. As for all the tricks and gadgets to feel the piston coming up on the compression stroke the only trick is to wet your thumb, press it tightly on the spark plug hole and rotate the crank in it's normal direction until you feel the pressure start building under your thumb. Then mount your dial indicator so it can read piston travel and measure for TDC. If the the plug hole is not above the piston then make a wiggler from metal rod and bend as needed and attach it firmly to your dial indicator.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[horse]

Thanks Wes for the information.
I did not rebuild the engine the Greek army did it a while ago so I have only their marks to go on and wanted to check if they are accurate or not.
Have you a picture of the wriggler and I will have a go at making one.

Ron thanks for the ideas. I have just done the sump gasket a few months ago so that is not an option. I do have a small camera but it just gave me a shot of the valve top.

See how I get on, thanks Horse.
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1952 M38

[wesk]

A lot depends on the attachment provisions of your dial indicator.



Usually just a reasonably hard object wedged between the head and the top of the piston will work as what we call a "piston stop". Then you can accurately move the piston up to the stop on compression until it physically hits the stop then mark the pulley or timing cover then rotate it 360 backwards until the piston hits the stop again and mark the pulley. Halfway between these two marks is the real TDC. Hint: Some folks use a very large plastic wire tie the 12" size for their adapted piston stop using the large tip inside the bore.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100

Mjeeps photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=Wes-Knettle&op=modload&name=gallery&file=index&include=view_album.php

[horse]

Nice idea with the plastic tie, I happen to have one of those.
I do not have a dial indicator so thanks for explaining how I should use the tie method. Roll on the weekend. Thanks Horse.
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1952 M38

[horse]

Wes, also found your explanation with photos back in Jan 14 titled TDC timing mark for M38A1 which is the same principle. Seek and you shall find, with a little help.
Horse.
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1952 M38

[horse]

Just to follow up after checking the timing using the thumb over the spark plug hole and using a pen to mark the front cover and pulley, difficult with the radiator in place, I am pleased to say that part of the timing is spot on. I did not use the plastic tie but bent wire instead sort of S shape.
I took a lot of time to check and set the points gap also using Wes paper method as the points just start to open when you turn the disi by hand. I found a lot easer to see with the rotor off. Nearly forgot to put it back on!
She started very smooth no put putting which I have been trying to get rid of in ages. Then onto the timing light but unfortunately my light has stopped working so no full end result.
While the engine was warm reset the carburettor with the vac gauge. All I can say she is running very well at idle will see what happens with the timing light and further up the rev range. Spending time on these items makes a big difference so thanks to all for your help. Next instalment next weekend hopefully. Horse.
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1952 M38

[horse]

So new timing light arrived ready for Saturday morning. The instructions on this one said to use a separate battery with 24V systems. I found out too late for my original one and wired it up to the front engine battery but did not put the earth onto the engine instead onto the negative of the battery. Somebody could tell me the difference but I know it eventually damages the light. Maybe earth onto the engine is 12V and onto the negative post is 24V ?

The static timing was nearly spot on but set the timing light onto 8 degrees BTDC to take advantage for modern fuels , she is running well.
I then reset the carb with a vacuum gauge with the revs as close as I could get to 600RPM with a laser off the front pully.

I thought last time I did this I had got it right but did not fully understand the static timing or proper use of the timing light which I do now. The advance you can see on the light when you rev the engine , it goes so far and stops which I understand is correct. Disi weights working well.

Went for a good run and pleased with the results. Hot start was instant and cold start the same this morning using the choke. Never had anything to do with points etc prior to M38 so pleased with the results, I can see other vehicles would be a bit easier to start on,thanks for the help. Horse
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1952 M38