Piston slap? Lifter knock? cold start knock? Read this first!!
08-22-2017, 11:08 AM
#1
CF Veteran
Thread Starter
Piston slap? Lifter knock? cold start knock? Read this first!!
There used to be a column for "what did you do to your Jeep today?" but I can't find it.
Anywho...
So my 97 4.0 has had this knock when I start it up for some time. Lately it's been worse. On a cold start, it is quiet, then after about a minute it starts, sounds like a lifter or two. Then after a few more minutes it quiets right down and is fine. However lately if I park for 10 minutes and restart it is right back and the whole process repeats. Fairly loud, it was getting worrisome and embarrassing, you could hear it a long way off.
With just turning 200k, I figure it may be time. So I start pricing valve jobs, machine shops, etc because you have to pull the head. Even started getting my spare XJ ready, just in case. Also I eliminate the exhaust manifold by checking bolts, sealing maybe cracks with goop. No difference. Did a good oil change to 5-20 with MMO added and an autolite filter. Ran better, still, still no difference in the cold start knocks.
Yesterday I got prices locally of $200-300 + parts (valves) from one shop and $375 - 450 from another, more reputable shop. The second shop says "Maybe you have piston slap."Gasp!! Piston slap, yes, I have heard of it with the 4.0's,...oh no...NOOO. The death knell for my ride, I would just get another before going through a block rebuild.
This morning I google Piston Slap 4.0, and come across an xj mechanic that said an old mech at his shop recalled a TSB about top end cleaning for jeeps to clear a carbon knock. He then did a top end cleaning, and (the light is going off in my head at this point) it worked for him. Another post from an old nuts mechanic said the same thing basically, and that with 200k on any motor you need to do this for carbon buildup or you can end up with knocks. Used to use just water and rpm's back in the day.
So I went to the garage and found 1/3 of a can of Seafoam..trickled it in to the throttle body on idle only,on the first cold start of the day..not enough to stall it because I don't believe it that method, (hydrolock with fluid can't be good)...and then shut it off for 20 mins. This is important to let it bind to the carbon!
Went out and started it and let idle 15-20 mins, Do not rev the engine! I mean to tell you, it smoked. Alot. The whole 20 mins. I thought, good! Burn baby burn. Then, got in and took for an easy but working short run up the road...just put it through it's paces easy...smoked for 1/4 mile more, but was quite smooth, and quiet, (not that it knocked when driving).
No more knock.
Idle was really smooth! Said ok, lets shut it off a while and see. Half hour later, started up, and smooth and quiet as a swiss watch. Well, I'll be d***ed.
Thank you, Seafoam. Hope this helps someone else with 200k miles to avoid the devastating mistake of tearing into lifters and a valve job that was misdiagnosed.
Even though I was certified in auto engine machine shop some 35 years ago, I was almost fooled. Don't be me. Well be me, cause in the end I figured it out.
Anywho...
So my 97 4.0 has had this knock when I start it up for some time. Lately it's been worse. On a cold start, it is quiet, then after about a minute it starts, sounds like a lifter or two. Then after a few more minutes it quiets right down and is fine. However lately if I park for 10 minutes and restart it is right back and the whole process repeats. Fairly loud, it was getting worrisome and embarrassing, you could hear it a long way off.
With just turning 200k, I figure it may be time. So I start pricing valve jobs, machine shops, etc because you have to pull the head. Even started getting my spare XJ ready, just in case. Also I eliminate the exhaust manifold by checking bolts, sealing maybe cracks with goop. No difference. Did a good oil change to 5-20 with MMO added and an autolite filter. Ran better, still, still no difference in the cold start knocks.
Yesterday I got prices locally of $200-300 + parts (valves) from one shop and $375 - 450 from another, more reputable shop. The second shop says "Maybe you have piston slap."Gasp!! Piston slap, yes, I have heard of it with the 4.0's,...oh no...NOOO. The death knell for my ride, I would just get another before going through a block rebuild.
This morning I google Piston Slap 4.0, and come across an xj mechanic that said an old mech at his shop recalled a TSB about top end cleaning for jeeps to clear a carbon knock. He then did a top end cleaning, and (the light is going off in my head at this point) it worked for him. Another post from an old nuts mechanic said the same thing basically, and that with 200k on any motor you need to do this for carbon buildup or you can end up with knocks. Used to use just water and rpm's back in the day.
So I went to the garage and found 1/3 of a can of Seafoam..trickled it in to the throttle body on idle only,on the first cold start of the day..not enough to stall it because I don't believe it that method, (hydrolock with fluid can't be good)...and then shut it off for 20 mins. This is important to let it bind to the carbon!
Went out and started it and let idle 15-20 mins, Do not rev the engine! I mean to tell you, it smoked. Alot. The whole 20 mins. I thought, good! Burn baby burn. Then, got in and took for an easy but working short run up the road...just put it through it's paces easy...smoked for 1/4 mile more, but was quite smooth, and quiet, (not that it knocked when driving).
No more knock.
Idle was really smooth! Said ok, lets shut it off a while and see. Half hour later, started up, and smooth and quiet as a swiss watch. Well, I'll be d***ed.
Thank you, Seafoam. Hope this helps someone else with 200k miles to avoid the devastating mistake of tearing into lifters and a valve job that was misdiagnosed.
Even though I was certified in auto engine machine shop some 35 years ago, I was almost fooled. Don't be me. Well be me, cause in the end I figured it out.
