M38A1 cold start problem

wesk · Posted: Fri Jan 27, 2017 11:06 am Post subject:

Also even though you are within the 90-110 parameter you still have a noticeable spread between your high and low cylinders. The industry standard is 10 % meaning the lowest cylinder must be within 10% of the highest cylinder. In your case 10 % of your high cylinder 106.7 will be 10.67. 106.7 - 10.67 = 96.03. Your # 1 & # 4 cylinders are both much lower than 96.03. This imbalance causes the engine to vibrate excessively increasing several parameter wear rates.

Most experienced mechanics when faced with your compression readings will followup with a leak down pressure check to determine the source of the compression loss on those two cylinders. The two primary sources are ring wear and valve leaks.

How the leak down test is performed and how to understand the results are here: http://www.gregsengine.com/cylinder-leakdown-testing.html

In a leak down test the allowable low reading is 30% of the highest cylinder reading.

I always do the leak down test on all cylinders.

Testers can be found in two configurations:

Single gauge

Double gauge

The double gauge is quicker and easier to use. They are priced from $30 to $150.
_________________
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

Brinken · Posted: Fri Jan 27, 2017 5:12 pm Post subject:

OK Wes, I have noticed this imbalance, especially when the engine is half-warm. I will go for your advice when the weather here allows so. I will try to borrow this kind of equipment rather than buy it. It will be quite an investment for a one time use.
Do you think an ordinary repair garage will have such an instrument?
Anyway, for the moment I am rather pleased with her running almost according to my wish.
Have a nice weekend.
_________________
//Jan-Olof
1961 M38A1
1955 Roset/Polynorm trailer
Photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=album453&op=modload&name=gallery&file=index&include=view_album.php

wesk · Posted: Fri Jan 27, 2017 10:34 pm Post subject:

Most repair garages in the US will have one. I am not certain about Sweden. Racing garages will certainly have them.

They are simple to build. two 0-100 PSI gauges. A block of aluminum. A .040" ( 1.0 mm) orifice type restriction. A fine low pressure regulator. Adapter fitting for spark plug hole.

Here's a "Do it yourself" site: http://www.evolutionm.net/forums/evo-how-tos-installations/481133-how-make-your-own-faa-spec-leakdown-tester.html
_________________
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

RICKG · Member Joined: Aug 31, 2010 Posts: 1741 Location: SO IDAHO

The DIY tester is now on my wish list, thx for the link Wes.
_________________
keep 'em rollin'
RICKG MC 51986 DOD 01-52, '50 CJ3a

Brinken · Posted: Sat Jan 28, 2017 3:54 pm Post subject:

Wes
Thank you for all information, I have downloaded everything to my simple chamber ponder newfound knowledge. I will study this thouroughly next week.
_________________
//Jan-Olof
1961 M38A1
1955 Roset/Polynorm trailer
Photo album: http://www.willysmjeeps.com/v2/modules.php?set_albumName=album453&op=modload&name=gallery&file=index&include=view_album.php


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