Iowa4Runner
New member
AK602 said:
Any news from your local dealer?
My 4Runner sounds like a Diesel
- Thread starter Iowa4Runner
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Any news from your local dealer?
Pistons rock as they cross TDC where the thrust load from the rod angularity shifts from one side to the other. This makes noise. Harmless, but it is the source of piston slap in most all situations.
To prevent this, pistons are designed with long, tapered, flexible skirts so that they can be fitted very tight in the bores when the bore and piston is cold. The taper of the skirt and flexibility of the skirt then prevents scuffing when the piston is hot. Also, the piston pin in OEM production pistons is always offset to one side....it is NOT in the middle of the piston. By offsetting the pin in the piston, artificial thrust load is created to control the piston "rocking" as it crosses over TDC.
Unfortunately, all of the above control techniques, common in past model engines to the extreme, create excess piston mass, cause friction and cost power and fuel economy. With the desire to build in as much power and free-revving capability and to improve fuel economy as much as possible thru friction reduction these design features are pushed in the other direction on modern engines.
Piston pin offset has been reduced over the years to a bare minimum today to reduce the thrust load generated and reduce friction. Pistons have been lightened up considerably by shortening the skirts. This creates less rotating/reciprocating mass which is good for power, free revving capability and fuel economy. Light weight pistons are great but the skirts, by necessity, are short making it hard to make them both strong and flexible and the shorter ckirts make them more prone to rocking.
Unfortunately, when the performance or fuel economy oriented pistons are run cold they are very prone to "slap" until they warm up to operating temperature.
The piston designers and development engineers are always treading the fine line between piston slap cold and friction and power/fuel economy loss when the engine is warm.
It is possible that you are hearing piston noise from an engine that is on the "high limit" for piston clearance so that it makes some noise cold. The good news is that the condition is harmless and that engine is probably a little more powerful (due to less friction) than a "quiet" counterpart. The bad news is that...it makes noise cold.
To prevent this, pistons are designed with long, tapered, flexible skirts so that they can be fitted very tight in the bores when the bore and piston is cold. The taper of the skirt and flexibility of the skirt then prevents scuffing when the piston is hot. Also, the piston pin in OEM production pistons is always offset to one side....it is NOT in the middle of the piston. By offsetting the pin in the piston, artificial thrust load is created to control the piston "rocking" as it crosses over TDC.
Unfortunately, all of the above control techniques, common in past model engines to the extreme, create excess piston mass, cause friction and cost power and fuel economy. With the desire to build in as much power and free-revving capability and to improve fuel economy as much as possible thru friction reduction these design features are pushed in the other direction on modern engines.
Piston pin offset has been reduced over the years to a bare minimum today to reduce the thrust load generated and reduce friction. Pistons have been lightened up considerably by shortening the skirts. This creates less rotating/reciprocating mass which is good for power, free revving capability and fuel economy. Light weight pistons are great but the skirts, by necessity, are short making it hard to make them both strong and flexible and the shorter ckirts make them more prone to rocking.
Unfortunately, when the performance or fuel economy oriented pistons are run cold they are very prone to "slap" until they warm up to operating temperature.
The piston designers and development engineers are always treading the fine line between piston slap cold and friction and power/fuel economy loss when the engine is warm.
It is possible that you are hearing piston noise from an engine that is on the "high limit" for piston clearance so that it makes some noise cold. The good news is that the condition is harmless and that engine is probably a little more powerful (due to less friction) than a "quiet" counterpart. The bad news is that...it makes noise cold.
Iowa4Runner
New member
SWUtah said:
While it may be harmless in most cases, piston slap can be a real problem. Some of GM's slap-happy engines have had significant wear and high oil consumption issues. I'd like to think my 4Runner is better built than any GM, but I'm not 100% sure. I'm going to send in an oil sample for analysis to get an idea if I really have something to worry about.
The last few days I've done some cold weather startup tests. Even on really cold days the engine sounds fine idling in park, no knocking even right after startup. If I put it in reverse or drive without letting it warm up for several minutes, I notice a hearty knocking sound. While sitting in park, if I bring the engine up to 2500 RPM (30 seconds after startup), I hear a higher pitched knocking / tapping clatter that seems more like a piston slap. It sounds kind of like my old worn out single cylinder 2 stroke dirt bike. It's definitely a higher pitch than the "hearty" knock I first described. I can't wait to see what ol' Bob the oil guy says...
Iowa4Runner said:
I would say that as long as you have a good UOA and your not using more then 1 quart of oil in a normal 3-5K mile OCI, you don't have a problem. If you start using a lot of oil or the UOA shows a lot of wear then I would have the Toyota dealer look at the problem. The dealer isn't going to do anything unless you have these problems. If you start using oil after the 5 year 60K mile warranty is up then I would trade it in before it gets any worse. The good thing even the owners of Tundra's that have reported the slap and one Landcruiser owner I've heard of with the slap, none have reported excess oil usage so they will probably get well over 200K miles out of these engines. I'm not trying to mitigate your concern, I also would be very upset if my 4runner or Landcruiser ends up with the piston slap and I hope I never get it. I'm just trying to ease your concern with the information that I have been able to gather on this issue. I agree that GM has a much bigger problem, since many of their engines with the slap have excess oil consumption and UOA showing increased wear. Not something we are seeing in the Toyota 4.7 V8. Good luck and let us know the results of your UOA on this thread.
PS- I would continue doing the warm-up in park without a load on the engine, this should help mitigate wear.
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