Does a rebuilt engine take some time to get the power back?

[KYJ10]

Ive only driven less than 50 miles since the rebuild, but it seems slugish and weak. I hoping it just takes some time cause everything is so tight so to speak. I felt like my old worn out motor, running on 7 cylinders would be my rebuild right now. It's also pinging slightly when I step on it. I forget, is that alittle off to retard or to much advance. Thanks, Dennis

[Stuka]

the engine need to break in for at least 750 miles before you go romping on it. The break-in period is crucial to an engine lasting. Those fist 750-1000 miles need to be taken easy, dont bog the engine, do rev it way up, and dont floor it (the extra gas may cause it to semmi-flood washing the oil off the cylinders, on a tight enngine this is a bad thing)

But yes a tight engine wont have as much power. As there is a LOT more friction. When ever I break in an engine, I idle it at varing RPM's for about 10 hours before I ever actually take it out on the road.

[rockjeep44]

Dennis, put it up on jackstands and run it for 1000 miles so you can romp on it when you get to tellico ;)

[Serious Johnson]

Dennis:

I agree with Stuka that more run-in time should be allocated before even testing the ultimate output. Still, if the thing feels wrong and you're getting some ping, then something ain't quite right.

I'd recommend double checking the ignition timing as a start. It's also possible that the cam timing is advanced a bit (new sprocket indexes can be off by a fair amount). Advanced valve events can result in higher cylinder pressures at low revs and nearly incurable ping. Unfortunately, it takes no small effort to verify appropriate valve timing. You pretty much have to put a degree wheel on the crank pulley and then determine actual TDC by direct observation.

Oh yes, to at least partly answer one of your questions: Ping due to incorrect ignition timing is always due to too much advance. That's not to say that incorrect advance is always the cause.

:-

[Chero77]

I agree with the above, but it sounds like something is wrong with your engine. A fresh rebuld should feel powerful right out of the box. Yes it should be run in, and after 15,000 miles or so it will "loosen up" and make more power, but there should be a night and day difference between a tired engine and a fresh rebuild. You say your rebuild feels like the old engine running on seven cylinders. Somethings not right.

[KYJ10]

yea, it just feels slugish and unresponsive. I probably need some carb work or something. Even b4 the rebuild, I started to stumble at about 50, and it acted similar on the 2 mile trip from the exhaust place today. I have a t18 and usually starting out in second is easy, no I have to really rev it or it just seems to bog down to a stall. I can rev it no load and it sounds and responds great, but under load, it just seems like the e-brake is on. I need to get this thing ironed out, so I can get some miles on b4 Tellico. Im so over budgeted it aint funny!

[Stuka]

hrm, check for vacuum leaks also. A vacuum leak will makeit have terrible low end. When I got one in my cherokee from a cracked cap it was hardly able to start out in 2nd also, and it just had terrible response.

[64Trvlr]

Originally posted by KYJ10:
Ive only driven less than 50 miles since the rebuild, but it seems slugish and weak. Did you break the cam in correctly? If not you may have one or more flat lobes on the cam which will make it feel like it's missing a cylinder or two. Did you put a vacuum gauge on it and see what you have? And maybe run a compression test too.
:cool:

[KYJ10]

I will do that. I was just running threw the grass alittle, and after the intial slugishness, I put my foot in it alittle and seemed ok. But nothing like I expect. It is also hard to start. Gotta be something little. I will spend some time on it Monday. Thnaks guys, Dennis

[KYJ10]

Yea, I broke the cam in b4 putting any load on it. My pocket book wants my MJ back!!!

[rockjeep44]

I'd definitely say that it's probably something little. There are a ton of things that could have gotten overlooked when swapping an engine (ie vacuum leaks). So, I'd start with fixing the carb and checking for leaks before you get into anything real serious.
-Andrew

[Joe Guilbeau]

Vacuum, timing, carb...

[JeepJerk]

Hydro lifters? Seen lots of new engines with the valve lash incorrectly adjusted because the lifters wern't fully pumped up before the lash was set. Check what the other members have recommened as well; base timing, vacumn leaks, faulty or miss adjusted carb. etc. Initial break in on a motor is critical. Before the truck leaves the shop I run for 20 minutes at no less than 1000rpm and no more than 1800rpm to ensure adaquate oil circulation, check everything, dump the oil, change the filter and then do it all again. Then again. Drive it easily on an open road for a 1000miles or so. Opinions seem to vary here, but after 2500 miles or so, motor should be broken in, power should be there, and should be rompable (is that even a word?). Keep in mind that as a motor breakes in the "tuning parameters change", carb and timing adjustments need to be checked.Is this a remanufactered motor or one you had rebuilt?

[jackz4000]

Agree. Something is wrong. I've been gently breaking in a 360 rebuild, original engine. Just hit 500 miles and it has plenty of power. Rides (so far) like a dream. Look for the easy things first, usually all the other parts in your used Jeep are breaking in to the new rebuilt engine. Also, on the install, something may have been missed...like a vacuum line or the carb. And be prepared for some small parts to just go. For me, so far the temp sending unit and the oil pressure sending unit have both quit. And I expect a couple other items in the near future to "bug-out". And don't romp on it....yet.