Real time compression test help.

[Rube]

trying to get this old truck back and running again. Set the valves to spec but may have left the back 3 a bit tighter than I would’ve preferred but nothing obscene. Went ahead and did a dry and wet compression test today with the following results. Should I go back and respec the valves or what? Vacuum sits right at 15mm hg and I’m trying to chase down that leak as well. All said, how bad does my engine look with the filling numbers?

1984 2f with 205k

Dry then wet numbers:
#1 125 & 165
#2 120 & 140
#3 120 & 145
#4 115 & 170
#5 140 & 155
#6 130 & 150

 

[OSS]

Those numbers don't warrant a block rebuild or valve job. They look 'normal' for the age of the engine. If you don't have confidence in your last valve adjustment, then check them again.

 

[Seth S]

Remember that at a compression ratio of 7.8:1 these are not very high compression. So if you live at sea level and we say air is 14.7 psi then at TDC firing with both valves closed you should see around 115psi in each cylinder.

Not sure what the FSM calls out for numbers. there are lots of little things that can affect the numbers but yours don't show any major difference to be worried about.

 

[Rube]

Thanks for the advice all. First time doing this and trying to undo the rats nest of “modifications” by the PO. Hopefully have it up and going sometime next week. Just need to replace the battery booster and rear brakes and she should be road worthy (I hope).

 

[gregnash]

If you haven't already go get the FSMs from the few threads (and/or my sig line) that are provided. Really will help with lots of stuff, also you can adjust the valves dry and cold instead of warming the engine up and then scrambling while it is still hot.

other than that she looks pretty normal and seems to be a fairly strong runner. What elevation are you at so we can tell what you really should be at for vacuum readings?

 

[Rube]

I’m at 400’ but haven’t been able to source out the remaining vacuum leak with carb spray. Managed to lean the mix and adjust idle today to get 17mm Hg. I’ll keep working at it. Considering trying a gasket between the carb and manifold as it’s the next easiest step.

 

[LAMBCRUSHER]

So looking at those numbers, go snuggy up cylinders 1-4 valves and try again...

 

[LAMBCRUSHER]

If it goes back down on those holes, then you may have some carbon build up in the back 2, but if you can get the front 4 closer to the back 2, you’d be stylin. Otherwise agree that it seems a runner. Even if all of them were at 120 ish...

 

[gregnash]

Ok at 400' you should be aiming for somewhere in the 20-21inHg.
Something lots of the guys talk about here, and I have yet to try but want to, is tuning the timing and engine via vacuum. May be worth a shot.

 

[Michael Hanson]

Hi, Are you in the south or east Arkansas ? Mike

 

[Rube]

Hi, Are you in the south or east Arkansas ? Mike

Central AR

 

[Seth_O]

Ok at 400' you should be aiming for somewhere in the 20-21inHg.
Something lots of the guys talk about here, and I have yet to try but want to, is tuning the timing and engine via vacuum. May be worth a shot.

Do you have a post you can point me towards for this? I've had several folks mention it, but no one talks about how they did it.

I can understand setting the timing by vacuum, but not the mix or idle?

 

[gregnash]

Do you have a post you can point me towards for this? I've had several folks mention it, but no one talks about how they did it.

I can understand setting the timing by vacuum, but not the mix or idle?

Sorry, same thing most just talk about doing it... Think most just go between how the engine sounds and the vacuum as they adjust idle mix, idle speed and timing. Then basically you just between the three to get your optimal idle. If the idle mix screw hasn't been touched then dont break into that yet, just hop between the timing and idle speed.

 

[Rube]

In my mind, it’s makes sense to set timing first, then idle speed, then mix but I’m sure someone can weigh in with an expert opinion as to why and what process would be best.

 

[Michael Hanson]

Hi, You would be fine with that approach. We have a home in the Hot Springs area. If your around there and need help we go up there often. Mike

 

[gregnash]

In my mind, it’s makes sense to set timing first, then idle speed, then mix but I’m sure someone can weigh in with an expert opinion as to why and what process would be best.

You could be correct. Only caveat would be that I would set timing then maybe do the lean drop method found in the FSM to tune.

 

[Rube]

You could be correct. Only caveat would be that I would set timing then maybe do the lean drop method found in the FSM to tune.

I've tried the "lean drop" method and am sure its far easier than I tend to make it but can't ever seem to really figure it out (I can be quite simple). Anyone have additional input or video even?

 

[NeverGiveUpYota]

Its a wenchy thing to understand and grasp. I only felt I got it right once while I had @mwebfj60 on the phone. Turning the IM in or out if the truck starts to idle poorly then you know you have gone too far. That's about as much as I remember. Keep a timing gun hooked up and a vac gauge and watch both and see how they react as well. Its a total science for sure. But all that is very very dependent on how good your gasket is sealing is at the intake manifold and all the other vac lines that suck.

 

[OSS]

vac lines that suck

I guess that pretty much sums up the situation under the hood of a FJ60. Ha!

 

[NeverGiveUpYota]

Exactly. I have fun saying it as much I have in typing it.