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Pulley timing mark

 
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lucianom38a1
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Joined: Jun 14, 2005
Posts: 25
Location: So Paulo - Brazil

PostPosted: Thu Sep 22, 2011 10:31 am    Post subject: Pulley timing mark Reply with quote

I was trying to set the ignition timing on my M38, using the strobo timing light.
As per the manual, the pulley mark is a small dot, that should appoint to the BTDC or to the correct 5 degrees when in idle. But in my case, its running about 26 degrees advanced!

I started to rotate the distributor, trying to make the small dot match tje -5 degrees (based on the strobo indication - the lamp advance knob was set to zero), but the engine started to run unstable (clearly out of timing).

The original crank pulley was substituted in the past from another M38 pulley. So its not original, but its a M38 pulley.

Looking for an anternative, I saw in the manual that there is a hole close to the engine starter, that allows to see another timing mark. But I didnt found this on my jeep.

Any idea how to set the timing?

Thanks
_________________
1942 Dodge Command Car WC57
1951 M38
1955 M38A1

MPVA 31769
www.apvma.com.br
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Bretto
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Joined: Nov 24, 2010
Posts: 1121
Location: Orem, UT

PostPosted: Thu Sep 22, 2011 10:38 am    Post subject: Reply with quote

Mine is all jacked up and cant explain why but my pulley mark is off and there are no marks on the flywheel. I had to take Wes' direction and find #1 TDC by fishing a wire down the spark plug hole and then making a ref mark on the pulley. I dont know where the link to his direction in but I bet he'll chime in.
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'51 M38
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lucianom38a1
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Joined: Jun 14, 2005
Posts: 25
Location: So Paulo - Brazil

PostPosted: Thu Sep 22, 2011 11:49 am    Post subject: Reply with quote

Bretto,

Is it possible to create a new precise timing mark with this process?

I believe thats my only option, since Im doing it now by just "listening the engine". Considering this terrible kind of gasoline that we have here in brazil, with more than 25% of ethanol, the engine doesnt run smooth in any circunstance.
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1942 Dodge Command Car WC57
1951 M38
1955 M38A1

MPVA 31769
www.apvma.com.br
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wesk
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Joined: Apr 04, 2005
Posts: 10174
Location: Wisconsin

PostPosted: Thu Sep 22, 2011 8:24 pm    Post subject: Reply with quote

The early M38 came with the early bell housing and flywheel and the timing mark was on the flywheel and the bell housing adapter plate had the small window.

The later M38 had the late bell housing with the late flywheel and no timing mark on the flywheel and no window.

It was common practice in the military to make a timing mark on the front timing gear cover and the front crank pulley using the rear flywheel mark as a reference on the older jeeps. This has led us to 50 years later with a very good mix of M38 engines and parts. This means until you confirm the accuracy of your timing marks they are not reliable.

Before doing any of this make sure the distributor is healthy. The point gap is correct. The idle speed is correct .

How to do this depends on just how accurate you want to be. Before we get into this you need to study your parts and your manual until you understand fully the meaning of:
engine normal rotation direction of crankshaft.
distributor rotor normal rotation direction
which rotational direction movement of the distributor housing equals advancing and retarding.
the extra loads placed on the starter when leaving timing advanced too far.
how to locate top dead center (TDC) on compression of a cylinder.
why the piston will stop moving upwards for several degrees of crank rotation while the crank continues to turn through TDC.

The real art of finding TDC is determining how many degrees of travel the crank makes thru TDC with no movement of the piston. Where this piston movement stops and where it begins again. Then dividing that distance in half to locate the true TDC.

Once you have a very good grasp on the principals above we can proceed.

Most accurate method of locating TDC and then locating 5 degrees BTDC is:
1-Bring #1 piston almost to TDC on compression stroke. Piston about
2/3rds the way up the bore on compression.
2-With head removed using a dial indicator riding on the top of the piston very slowly move the crank in it's normal direction of rotation until the piston stops moving the dial indicator. With a felt marker or crayon make a match mark on the front timing gear cover and the crank pulley. Now continue rotating the crank in it's normal rotation until the piston movement starts again and stop instantly. Make another mark on the crank pulley to mate with the mark you previously made on the timing gear cover. Halfway between those two marks on the pulley is the true TDC mark. Make that new true TDC mark and erase the other two marks on the pulley.
3-Place a degree wheel on the crank pulley and make a mark 5 degrees BTDC on the crank pulley based on the crank's normal direction of rotation. This mark will be towards the driver's side of the left hand drive jeep.

Note: If you wish you can reverse the markings so the crank pulley gets the single mark and the timing cover get's the TDC and 5 Deg BTDC marks. You can even buy a timing pointer that bolts to the timing gear cover bolts and already has the TDC and 5 DEG BTDC marks on it and all you need is the true TDC mark on the pulley.

If you do not want to remove the head or do not know how then a less accurate method is to use a wiggler through the #1 spark plug hole to determine the piston positions. This requires a lot of delicate feel in your hands. But it will get you close.

A even less accurate method yet is to use a vacuum gauge and simply adjust the timing until you get the highest steady reading vacuum . Then retard the distributor housing about 2 or 3 degrees of rotation. Check this new setting by trying to restart the engine after it sits for about 5 minutes. If the starter labors too hard then you must retard the distributor housing a couple more degrees.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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lucianom38a1
Member


Joined: Jun 14, 2005
Posts: 25
Location: So Paulo - Brazil

PostPosted: Fri Sep 23, 2011 7:33 am    Post subject: Reply with quote

Wes,

Thanks for you very accurate explanation. Ill try to do it without remove the head.

My idea is to fix the caliper on the plug hole (I dont kno how), and using that caliper bottom pin, rotate the crank clockwise, up the piston stops on top. I can do the same counterclockwise to find it in the other direction.

After find the TDC, I can use the strobo lamp adjustment to find the -5 degrees.


Thanks!
_________________
1942 Dodge Command Car WC57
1951 M38
1955 M38A1

MPVA 31769
www.apvma.com.br
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wesk
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Joined: Apr 04, 2005
Posts: 10174
Location: Wisconsin

PostPosted: Fri Sep 23, 2011 10:40 am    Post subject: Reply with quote

I must caution you that reversing the crank rotation for the beginning and end of piston movement will introduce a slight error. Try to realize the timing gears, the oil pump and cam drive and driven gears all introduce play or backlash to the system. By turning the crank only in it;s normal direction of rotation we take up this slack one time and we do not change it throughout the marking process. By reversing the crank for location of the downward start of the piston you are introducing a different amount of backlash from the side's of the gear teeth that normally get very little wear.

The spark plug hole is no above the piston so we must make a fixture that will place our motion detector over at the piston. The wigler I mention is a piece of wire bent in a very unusual "S" shape to go from the spark plug hole over to the area the piston travels in.
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Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
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lucianom38a1
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Joined: Jun 14, 2005
Posts: 25
Location: So Paulo - Brazil

PostPosted: Fri Sep 23, 2011 11:52 am    Post subject: Reply with quote

Wes,

I agree with you. Also I just realize that the piston is offset from the spark plug hole.

I found some tips how to do it at Vernco website: http://www.vernco.com/Tips/id337.htm

Thanks
_________________
1942 Dodge Command Car WC57
1951 M38
1955 M38A1

MPVA 31769
www.apvma.com.br
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