I need very basic motor rebuild advice (1 Viewer)

[fyton2v]

Hi. I've been chasing a small hesitation issue for a while ... and prior to that I was chasing a pinging issue under load, which was solved by more compatible timing and higher octane fuel. Forum folks theorized that the pinging was probably caused by carbon buildup on the pistons. That was really good theory. It's one of those things where you kinda don't want to know the truth. I kicked that can down the road.

But here we are. I bought an endoscope and did a long overdue compression test. Cyls 2 - 4 are not good. Cyl 1 is at 145psi. I did that one first and and I thought this is going to be excellent! Not so much. Cyl 2 - 4 are about 115psi and 5-6 are in the 130s. I don't burn much oil. No white smoke. No coolant/oil smoothie. Passed smog not too long ago, too ... so probably valves and seals. I'll post some pictures later, but I finally got a look at my pistons and there is quite a bit of carbon buildup, and the piston edges are worn and chipped. The cylinder walls seemed unmarred, but I need to do more poking around there.

So here is my very basic question. Is it at all possible (or advisable) to inspect bearings, cylinders, etc. and replace pistons without pulling the motor? Like ... if my cylinders don't need to be bored, do I really have to yank the motor out of the truck? Thanks.

 

[greenbeasty]

I would do a second compression check, I'm assuming you had the throttle pinned open, and all plugs out. I'd also do the wet test and see how all those numbers match.
Personally, I would not tear into it , based on visual, if there is not a problem with performance.
Old school mechanics used to trickle water in the carb with the engine warm, giving enough throttle to keep it up at a decent RPM, to clean carbon off the pistons and valves.
To answer the question, yes, you can do an in-frame refresh.

 

[4x4veteran]

Don't do it halfassed. It will cost more for a complete rebuild but cheaper in the long run.

 

[middlecalf]

So here is my very basic question. Is it at all possible (or advisable) to inspect bearings, cylinders, etc. and replace pistons without pulling the motor?

Yes on the “possible.”

 

[Green Bean]

Some folks have had good results with Seafoam and Lucas Oil additive. Might be interesting to see if your compression numbers improve.

 

[Pitter Patter]

Totally possible but it is really easy to pull an engine out of an FJ40. I feel like leaving it in is less work up front and more work during the process. Plus, there are things you will find when it’s out. Maybe you have a broken or worn mount? Pretty difficult to replace the casting plugs on the rear of the head and block while it’s up against the firewall. Easy to do a clutch if it’s out. Just pull the engine, you’ll be thankful you did.

 

[fyton2v]

Ok. Will do more tests this weekend. I think I'll try the water thing. I'll shove a garden hose down one of the carb barrels, open the hose nozzle, and floor it.

 

[Skreddy]

You can check bearings by just dropping the pan then taking off rod/main caps. Checking cylinders you’ll really need to pull the head. You can change valve seals with the head on.
Everything else in good shape: ignition, vacuum (no vac leaks), carb tune? Don’t look for what you don’t want to find….

 

[pjohnson]

Poor compression is not caused by carbon build up, it's either rings/cylinder wear or valves. Both of which will cause some level of burning oil. You say it's not making smoke, just using a bit of oil. Can you measure how much over a period of time? What do your plugs look like? Are they oil fouled? Determine if you are actually burning oil and just don't notice it. When you see the smoke is an indicator of where the problem may be.
As has been mentioned, re-do the compression test with throttle wide open, both dry and with a squirt of oil. It wouldn't be the first time an initial compression test was incorrect. Include a leak down test to cover all bases.
You suspect valves and seals, which is actually a good possibility.

Do more diagnostic testing before you tear it all apart.

 

[fyton2v]

Yes, more testing needed. Some of the plugs were fouled with oily/carbony build-up. Otherwise, truck is pretty good mechanically. I've never measured oil consumption though. It doesn't see many miles so I don't have to watch the oil very closely. No vacuum leaks, recently rebuilt carb, and the last time I tuned things (maybe last Fall) it was sucking something around 16.5 or 17 psig.

Like the motor, there are other things on this truck that haven't been rebuilt since 1978. On my to-do list are transmission and transfer case rebuilds. New seals are needed there, those components work well enough so I wasn't in a rush to do it. I haven't planned the work yet but yanking those things would probably be easier without a motor sitting there. Not really sure though. Maybe it's time to just do it all at once and put the truck to bed for a while. This isn't work I'll be able to do quickly; too many things higher up on the list.

 

[fyton2v]

Oh, and yes. The throttle was wide open during the compression test.

 

[Fjtdi]

This stuff works really well also.

 

[fjc-man]

When were the valve clearances last checked / ajusted?

 

[fyton2v]

When were the valve clearances last checked / ajusted?

Moments before the compression test. They're good.

 

[Pighead]

This stuff works really well also.

I like this stuff for de-carbonizing cylinders.

 

[Catching Neutral]

I have used seafoam before. Be aware that your neighbors will think your house is on fire.

 

[fyton2v]

I will be doing the Seafoam treatment this weekend. Will redo a compression test afterwards and then post some pics of the pistons to see how we all feel about it.

 

[pb4ugo]

There's no mechanic in a can. When I worked in a shop we used to use top engine cleaner for carbon build up. Pour about 1/2 a can it and keep it running then pour heavily and let the engine stall while emptying the can. Then let it sit for 1/2 hr our more. IDK if it actually did any thing, but create a lot of smoke. Oil has detergents in it, instead of using additives, just increase your oil change intervals and drive it. You mention it doesn't get driven much, that's not helpful. I bought my 40 off my brother who lived in Aspen. It was a valley car, meaning, it mostly stayed in and around the small city and up and down the mountains, and rarely on the highway for any length of time. I went out to drive it back home to Cincinnati straight through 24 to 30 hours and 1500 miles. At the start of the trip it would burn a quart of oil on every tank. About 2/3rds of the way I went to check the oil and to my surprise the dipstick showed full. It didnt use any, and didnt burn any more the rest of the trip. The constant running at 60mph+- for a 1000miles finally broke up all the carbon in cylnders, around compression and oil rings and probably the build up of carbon behind the valves. Drive it, get it up to temp for long periods, highway miles. Periodic hard acceleration to blow out the carbon. If your going to pull pistons, hone cyldrs, replace bearings and such pull the engine. In the end have the block cleaned and degreased, then wash it with soap and water to neutralize the solvents. Cleanliness is the key to a good rebuild.

 

[riderjgs]

You now have a running, driving vehicle that uses some oil. Beware the "while we're in there" syndrome that leads to long tear downs and "projects" that languish for years. The perfect is the enemy of the good. Oil is cheap. I'd try some of the other recommended easier steps before risking the possibility of a garage ornament. Enjoyment is much preferable to frustration.

 

[pjohnson]

"while we're in there" syndrome

Also known as the "Domino Effect"