Topic: Timing check CJ7 4.2 auto (Read 5351 times)

Dave69 · « **on:** January 08, 2014, 08:01:22 PM »

can anyone tell me the timing procedure for a 4.2 auto, 79 yr.

jeep runs smoothly no knocks starts fine but has no umph on hills so i can only assume the timing is out or retarded and might now need resetting or advancing.

it has what i think is the standard carb so i gather the vacuum advance will need to be disconnected to do this. from what i have read the timing BTDC could be a number of values.

current economy is approx 18mpg

Bubba · « **Reply #1 on:** January 08, 2014, 08:07:53 PM »

79 with qaudratrac ? If so cant far off to return 18mpg

Bubba · « **Reply #2 on:** January 08, 2014, 08:08:30 PM »

And the th400 soaks up some oomph

Lornaben · « **Reply #3 on:** January 08, 2014, 08:29:31 PM »

Don't forget the 4.2 doesn't make that much 'oomph' anyway.

Dutch · « **Reply #4 on:** January 08, 2014, 08:37:13 PM »

Dave, You on standard tyres ?

Mine on 31's ..... forget up the hill. Tuck in behind the truck on the inside lane at 25Mph.

The big dipper at Mc Donalds Kingsley/Fraddon is a killer

17/18 around town and 24 on a run sounds about right.

Mike Pavelin · « **Reply #5 on:** January 08, 2014, 08:43:36 PM »

Werd. A 258 ain't the weapon of choice when one has a skin to haul off one's rice pudding

Bulldog67 · « **Reply #6 on:** January 08, 2014, 08:45:07 PM »

And so it begins

Dave69 · « **Reply #7 on:** January 08, 2014, 10:21:32 PM »

its running 31's but i'm comparing it to the cherokee i had, maybe a big mistake.

any hill and the wifes 1200 beetle will out drag it, i would have thought there would be some torque in the old gal to pull it up hills. Given the slightest incline and it slows down, i am imagining the off road capability will be a joke if a slight embankment is tried let alone a hill like at ribbo with it in its current state. just seems the throttle is either fully on or off.

not asking for much just the lack of embarrassment of all the sound and no forward propulsion. would a carb upgrade help. just thought that if traveling at 40 it would do the same up a gradual hill.

Bulldog67 · « **Reply #8 on:** January 08, 2014, 10:27:30 PM »

I know I'm not a tech guru Fave but having driven a few now over the years of course it shut fly up a hill no problem, so something is Def wrong

Bubba · « **Reply #9 on:** January 08, 2014, 10:53:21 PM »

I have a webber carb you can have for it

Brynjaminjones · « **Reply #10 on:** January 09, 2014, 12:25:08 AM »

Quote from: Dutch on January 08, 2014, 08:37:13 PM

The big dipper at Mc Donalds Kingsley/Fraddon is a killer

Mwah ha ha, my XJ can out-accelerate many things up that hill, including some BMW 3-series coupe thing that for some reason took a disliking to me the other day!

Dave69 · « **Reply #11 on:** January 09, 2014, 06:46:07 AM »

i know the capabilities of an XJ so i am basing a comparison on that which the 4.2 engine should be powerful enough to at least drive with ease and hills shouldn't be an issue.

Thanks Kev i'll take that off your hands and see if there is an improved change. I'll sort out the details later.

Dave

Dutch · « **Reply #12 on:** January 09, 2014, 09:24:42 AM »

Quote from: Dave69 on January 08, 2014, 10:21:32 PM

i am imagining the off road capability will be a joke if a slight embankment is tried let alone a hill like at ribbo

not asking for much just the lack of embarrassment of all the sound and no forward propulsion.

just thought that if traveling at 40 it would do the same up a gradual hill.

Nope you can't compare it to anything else in road conditions in 2H. With the 31's the grunt simply isn't there.

Unless you max it out in 2nd up the hill by which point ye old 4.2 is ready to jump outta the truck or shit itself, whichever comes first. (this is also referred to as the Bulldog manoeuvre ......

)

In the dirt however in 4L there is very little that will stop it depending what rubber you are on (and who's on the loud pedal) so no embarrassment there.

j33pky · « **Reply #13 on:** January 09, 2014, 11:11:32 AM »

What axle ratio? My 5 when it had a 3.8 was quite good. 4.27 axles but was manual on 31" big muds. Not sure mpg.

j33pky · « **Reply #14 on:** January 09, 2014, 11:13:39 AM »

14-15 mpg at a guess

Bulldog67 · « **Reply #15 on:** January 09, 2014, 11:59:32 AM »

Quote from: Dutch on January 09, 2014, 09:24:42 AM

Quote from: Dave69 on January 08, 2014, 10:21:32 PM
i am imagining the off road capability will be a joke if a slight embankment is tried let alone a hill like at ribbo

not asking for much just the lack of embarrassment of all the sound and no forward propulsion.

just thought that if traveling at 40 it would do the same up a gradual hill.

Nope you can't compare it to anything else in road conditions in 2H. With the 31's the grunt simply isn't there.

Unless you max it out in 2nd up the hill by which point ye old 4.2 is ready to jump outta the truck or shit itself, whichever comes first. (this is also referred to as the Bulldog manoeuvre ...... )

In the dirt however in 4L there is very little that will stop it depending what rubber you are on (and who's on the loud pedal) so no embarrassment there.

Bulldog rocks

Dutch · « **Reply #16 on:** January 09, 2014, 12:36:23 PM »

Quote from: j33pky on January 09, 2014, 11:11:32 AM

What axle ratio? My 5 when it had a 3.8 was quite good. 4.27 axles but was manual on 31" big muds. Not sure mpg.

Bog standard me thinks, whatever that is.

Dave69 · « **Reply #17 on:** January 09, 2014, 08:47:37 PM »

as for axle ratio i haven't a clue, probably being over cautious but just getting my head around the quirks of an older jeep. i'll probably will be impressed when in 4L but it does feel like the throttle is fully open at all times apart from when coasting down a hill

Dutch · « **Reply #18 on:** January 09, 2014, 09:25:22 PM »

How's the steering coming along...... half a turn left - half a turn right ...... just to keep the bugger outta the ditch

eastryjeep · « **Reply #19 on:** January 09, 2014, 11:19:14 PM »

Info requested as follows if standard build.
1979, 6/258 tune up data.
Manual.
Timing = 5* +- 2* (vac hose disconnected & plugged)
Curb idle = 700 +- 100 RPM
Spark plug = N13L or RN13L
Plug gap = 0.033 - 0.038 in.
Auto.
Timing = 4* +- 2* (vac hose disconnected & plugged)
Curb idle = 600 +- 100 RPM
Spark plug = N13L or RN13L
Plug gap = 0.033 - 0.038 in.
Other years are all over the place but this should be yours.
Standard carb was a single barrel Carter YF or YFA (ditched mine for a Weber 38DGAS tho a 36/36 would probably have been a better choice), or the alternate was the Carter BBD or BBD2 double barrel carb.
Diff ratio on my 1977, Auto 4.2 CJ7, is 4.1:1 if that helps but a previous owners may have done any number of things since original build. Best way to check is to jack the front up, put a chalk marker on the prop shaft and turn the drive wheel. Just count how many times the wheel rotates for one go of the prop.
Being a 4x4 jacking the front is a bit safer as both the braked rear wheels stay on the ground and the bastard doesn't roll away. Remember, safely does it!

Dave69 · « **Reply #20 on:** January 10, 2014, 08:52:56 PM »

Quote from: Dutch on January 09, 2014, 09:25:22 PM

How's the steering coming along...... half a turn left - half a turn right ...... just to keep the bugger outta the ditch

there is a bit of play but now where near what i was expecting. Just looking forward to summer and roof down.

thanks Eastryjeep that's alot i can work with.

Author Topic: Timing check CJ7 4.2 auto (Read 5351 times)

Mike Pavelin

j33pky

j33pky

eastryjeep