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Piston Pin to Bosses Tolerance

J Ruiz

By J Ruiz
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J Ruiz Enthusiast

J Ruiz

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2008 Silverado LT 1500 LY5 Engine

How much tolerance is allowed in the rod to piston bosses. Mine have quite a bit of play when the cap is off and beleive it is slapping.

Jsdirt Senior Enthusiast

Jsdirt

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Your question has me cringing with all the things that could be wrong with this engine, in addition to excessive piston pin to piston clearance.

 

With these engines, cracking them open is a rarity, at least for me. Any customer couldn't pay me enough to go fishing around in these. Much easier and cheaper in the long run to just do a crate engine. Especially an AFM engine like the LY5 is. From 100k on, if the lifters haven't failed yet, the clock is ticking. Depending on the mileage, no matter what you fix internally, something else is bound to fail later down the road. With the amount of labor required to tear these down, I highly recommend a crate engine. You'll thank me later.

 

CamGTP Senior Enthusiast

CamGTP

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LS engines are some of the most simple V8's ever made, they are like 350 small blocks.

 

I've never seen a spec for what you are talking about, probably because I've never heard of anyone needing to look for that sort of information. Remember here that metal does expand so when the piston/rod/pin are hot the same play make not be there. You'd think if the pin was bouncing around in the piston you'd have broken it by now.

Jsdirt Senior Enthusiast

Jsdirt

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I beg to differ on that. It never took even close to 20 HOURS labor to change lifters on a 350, nor did I need a special alignment tool just to change a rear main seal. I hate the LS, as a mechanic. Mechanically the worst engine I have ever owned.

J Ruiz Enthusiast

J Ruiz

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6 hours ago, Jsdirt said:

I beg to differ on that. It never took even close to 20 HOURS labor to change lifters on a 350, nor did I need a special alignment tool just to change a rear main seal. I hate the LS, as a mechanic. Mechanically the worst engine I have ever owned.

Thx for the input. Your right about the time though because I can tear the heads off in an hour.

J Ruiz Enthusiast

J Ruiz

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6 hours ago, Jsdirt said:

I beg to differ on that. It never took even close to 20 HOURS labor to change lifters on a 350, nor did I need a special alignment tool just to change a rear main seal. I hate the LS, as a mechanic. Mechanically the worst engine I have ever owned.

Thx for the input. Your right about the time though because I can tear the heads off in an hour.

 

7 hours ago, CamGTP said:

LS engines are some of the most simple V8's ever made, they are like 350 small blocks.

 

I've never seen a spec for what you are talking about, probably because I've never heard of anyone needing to look for that sort of information. Remember here that metal does expand so when the piston/rod/pin are hot the same play make not be there. You'd think if the pin was bouncing around in the piston you'd have broken it by now.

 

7 hours ago, CamGTP said:

LS engines are some of the most simple V8's ever made, they are like 350 small blocks.

 

I've never seen a spec for what you are talking about, probably because I've never heard of anyone needing to look for that sort of information. Remember here that metal does expand so when the piston/rod/pin are hot the same play make not be there. You'd think if the pin was bouncing around in the piston you'd have broken it by now.

Good point on heat causing expansion.

Doug_Scott Senior Enthusiast

Doug_Scott

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Your not really clear on your question.  If you can physically move the piston up and down and see movement between the piston boss and wrist pin, that should have grenaded long before you took it apart.  The forces that occur when the piston has to stop and change direction 20 times per second at idle are immense and should have broken through the boss by now. 

If you mean the side to side play in the connecting rod to piston that is completely normal.  I do not know what this "cap" is you mention, unless you mean the connecting rod cap.  That is at the opposite end of the rod/piston assembly though.  Piston slap is normally caused by the piston "rocking" in the bore as it changes direction.  Short skirted pistons are more prone to piston slap, and modern engines have very short skirts compared to previous generation engines.

 

Both Jsdirt and myself are mechanics from when things were simple.  I started just before electronic ignition became common and still have my dwell gauge. Back when a matchbook came with a tool to gap points with.  And BIC made pens, not lighters.  With the tools and knowledge, the time to complete a job has little to do with difficulty, it just takes longer.

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J Ruiz Enthusiast

J Ruiz

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13 hours ago, Doug_Scott said:

Your not really clear on your question.  If you can physically move the piston up and down and see movement between the piston boss and wrist pin, that should have grenaded long before you took it apart.  The forces that occur when the piston has to stop and change direction 20 times per second at idle are immense and should have broken through the boss by now. 

If you mean the side to side play in the connecting rod to piston that is completely normal.  I do not know what this "cap" is you mention, unless you mean the connecting rod cap.  That is at the opposite end of the rod/piston assembly though.  Piston slap is normally caused by the piston "rocking" in the bore as it changes direction.  Short skirted pistons are more prone to piston slap, and modern engines have very short skirts compared to previous generation engines.

Thx you have answered my concerns regarding the piston pin movement.

Both Jsdirt and myself are mechanics from when things were simple.  I started just before electronic ignition became common and still have my dwell gauge. Back when a matchbook came with a tool to gap points with.  And BIC made pens, not lighters.  With the tools and knowledge, the time to complete a job has little to do with difficulty, it just takes longer.

 

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