piston slap? how bad is this?

[dmede808]

1986 fj60. 2f engine has a constant knock at idle that increases in speed with RPMs but can’t be heard once your up into higher gears. At idle or just under load in first gear it’s most noticeable. It seems slightly off beat, like it’s not a consistent tap or knock but rattles around a bit. When warm and starting off in 1st or 2nd gear I often get a loud dieseling sound from the engine (sounds just like a diesel). I’ve tried to locate it with my stethoscope but I can’t pinpoint it. I’m sure it is not the top end or the fuel pump.

My guess is this is piston slap (or wrist pin knock?). I more or less understand what piston slap is but what does this mean for the life of my truck? What can I do about it short of a rebuild and how reliable is my engine like this?

thanks,
dave

 

[PAFJ]

It almost sounds like your engine could be pinging. Do a search for pinging, you should find some good info.

 

[dmede808]

The dieseling may be related to pinging, I get some pinging on steep inclines at full throttle. But to my ear the dieseling sound is not quite the same as I would get with pre ignition.

The other sound, the tap or knock at idle and higher revs is not pinging however. Definitely mechanical, most likely piston slap.

My main question is, if it is piston slap, what does that mean for the life of my engine? I take long trips up to the Sierras and from the SF Bay Area to Oregon and I don't want to get stuck someplace with a busted engine. I can't rebuild right now, so what other options are there? I'm already running 20w-50.

 

[PAFJ]

So...do you have a lot of smoke, burning oil, etc.? What type of oil are you using? A heavier grade oil might help a little. I don't really know enough about piston slap to say how long your engine will last. I would guess probably not long...IMO.

Edit- Oops...just saw your running 20w-50.

 

[dmede808]

no smoke that I can see. 20w-50. Burns about a quart every 600 miles of heavy driving. Less if it's just around town. I've had my mechanic look at it once before and all he could really say was there wasn't much to do about it right now. Ive had other crusier drivers say they lived with piston slap for years with no ill effects. Just wondering what others think about that and if there were ways to fix it without a full rebuild (doesn't seem like it would be worth the cost unless doing a complete rebuild though).

I'm getting tired of having to deal with my old LCs problems (previous truck was a fj55) so I'll probably sell this one in a year or two if it makes it. If I could do a 2f rebuild with 5 speed trannny for under $7k I'd do that instead, but I don't think thats very likely.

 

[bram]

A quart in 600 miles is a lot. Do a compression test to see if your rings are smoked (they most certainly are with that amount of oil consumption). At some point the slap is going to cause some part to fail and then your motor will be dead. Hopefully you wont be in the sierras when it happens =)

 

[cruiser88]

sounds like you need to adjust your valves which is what im doing this weekend,they sound real loose according to your description

 

[lathrop]

sounds like you need to adjust your valves which is what im doing this weekend,they sound real loose according to your description

Here is a real old time thing to try. Put in a 50/50 mix of 20 w. and diesel in the crancase. run it for an hour or so. then drain replace filter. run for a few hundred miles. then replace filter or oil and filter.
A slight variation is to use automatic transmisioon fluid instead of diesel. It does a bettor job of cleaning the engine. If the problem a frozen ring it could help. and yes it will smoke.
Mine has 180k No oil burn. and clean oil.

 

[wesintl]

It could last 10k or 100k, It just depends. Do a compression test and find out what piston it is. Pull the head and pan and replace that piston. reassemble

 

[grant5127]

Additives and oils containing high levels of molybdenum disulfide ease the friction points associated with piston slap...also aids in oil consumption problems...I would consider getting the root of the problem tho.... your motor could be a time bomb... exploding when one least expects it......

 

[grant5127]

Here is a real old time thing to try. Put in a 50/50 mix of 20 w. and diesel in the crancase. run it for an hour or so. then drain replace filter. run for a few hundred miles. then replace filter or oil and filter.
A slight variation is to use automatic transmisioon fluid instead of diesel. It does a bettor job of cleaning the engine. If the problem a frozen ring it could help. and yes it will smoke.
Mine has 180k No oil burn. and clean oil.

Due to the nature of the new "ultra low sulfur diesel" I would not advise it at all.. cleaning with diesel is old school, with old school diesel integrity in mind...

 

[Tinker]

Sounds like you've decided it's piston slap without doing any investigation. Buy/borrow an automotive stethoscope & poke around. You'll narrow down the source of the noise.

Piston slap is caused by excessive side clearance between the piston & cylinder wall. When the piston "slaps", it cocks in the cylinder & unseats the rings. You should have low compression on the offending cylinder.

A leak-down test will tell you more about the condition of the valves & rings at TDC, but the compression test would be more indicative of piston slap.

Get the evidence first!

 

[dmede808]

Thanks for the replies guys. I agree, it's a time bomb and not much I can do about it until next year.

Tinker I decieded it was piston slap after doing several investigations since I first noticed the sound. I have not done a compression test since first bought but I have used my stethoscope on the engine, pulled plugs while running, paid close attention to what happens and when with regard to RPM's loading etc. I figure piston slap becasue I ruled out most of the other culprits and becasue of the way the sound behaves. The dieseling clatter starting off in 1st is indicative of piston slap and so is the way the sound does not time to the firing cycle or decrease when plugs are pulled.

But your right a comp test and leak down will tell me more. The truck is going to my mechanic next month for other work so I'll have it done then.

thanks everybody.

dave

 

[LandoCalrizzi]

I think my 87 FJ60 is doing the same. What if anything did you end up doing? Is your mechanic Mudrak?

 

[diesellibrarian]

I think my 87 FJ60 is doing the same. What if anything did you end up doing? Is your mechanic Mudrak?

This thread is 17 years old, and the original poster hasn't been active on the forum since 2009. Just so you're not holding your breath waiting for an answer to your question...