How much damage from a 5-2 shift?

['78 SC]

Boxscore: 5 pistons dinged, 5 exhaust valves bent, 0 rod bolts stretched and 0 rod bearings damaged.

Tippy's right, it's hard to eyeball where the valve is relative to the seat. I tore the motor down based on the leak down results. As mentioned earlier, the worst valves would leak liquid poured into the chamber. None were visibly out of place, at least to my untrained eye. Gotta trust the measurements. Craig (cgarr) confirmed 5 bent exhausts but said it was not a hard hit.

Rod bolts all mic'ed out ok; no permanent elongation. I went through the exercise of torquing each one to correct stretch and recording the required wrench torque setting. I'll use this value when reattaching the rods to the crank.

Pistons are in good shape. The impact actually looked less severe once the carbon was cleaned off. Monogrammed, like Chris' pistons. A couple had a slight burr at the end of the contact area. Easily smoothed away.

So Bruce, Walt and others were right, re-do the heads, clean up the pistons and you're good. If this happens again , would I pull the rods? Probably, it's not that big of a deal and having the reusable ARP rod bolts makes it just a matter of the time to remove the pistons (which I planned to do for the cleanup) and put it all back. But we'll burn that bridge when we get to it.

[Tippy]

My pistons have very deep grooves from the money shift, and I reused them for 5 years now with LOTS of boost.

You'll be fine.

I pulled the motor down awhile back again and no indication of a problem (cracks).

[faapgar]

Depending on the contact a rod bearing can get a flat spot on an over rev and fail a few thousand miles later.Do it once and do it right.ARP bolts rule for strenghth.

[Tippy]

Originally Posted by faapgar

Depending on the contact a rod bearing can get a flat spot on an over rev and fail a few thousand miles later.Do it once and do it right.ARP bolts rule for strenghth.

Not saying you're wrong, but I can't see that happening. Kissing a valve is not much stress. I put fairly deep pockets in my forged pistons and broke every valve guide and the rod bearings looked flawless during my "money shift".

Flat spots in rod bearings are normally from detonation.

Probably just a coincidence to find flat spots after a money shift which were related to detonation IMO.

['78 SC]

Interesting. What does this "flat spot" look like? Is it caused by journal to bearing contact when the load overcomes the oil film?

[cgarr]

The exhaust valves were barely bent, can't even tell looking at them. About .020 out on the grinder.


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[IMR-Merlin]

I am re-doing a 2.7 where the previous mechanic forgot to tighten down the cam sprocket nut... I have intake and exhaust valve marks on 4-6. I am getting 90-95% leakdown. I wonder how strong the 2.7 bottom end is...

['78 SC]

Craig (cgarr) at G2 caught this when he rebuilt the heads:



I suppose this is one more casualty of the over rev. It's not clear to me how a piston smacking a valve would crack the retainer (wouldn't the valve stem just slide through the retainer?), but the shock or any lateral movement of the valve could put excessive force on the retainer. Didn't I read here the retainers are sintered metal?

Anyway, the bottom line is check the heads thoroughly, even if the valves appear to seat ok (which mine didn't).

[Steve@Rennsport]

Originally Posted by '78 SC

It's not clear to me how a piston smacking a valve would crack the retainer (wouldn't the valve stem just slide through the retainer?), but the shock or any lateral movement of the valve could put excessive force on the retainer. Didn't I read here the retainers are sintered metal?

There are valve locks (keepers) positioned on the stem to keep the valve from both dropping into the chamber and being driven up through the spring retainer.

2.7 and older engines had machined steel retainers; 3.0 & later engines all have sintered metal ones.

[Walt Fricke]

The spring ends would which surround much of the retainer would tend to hold the retainer together enough that the keepers didn't fall out - especially if you decided to be gentle with the throttle and RPMs until you could get the car somewhere to get the engine checked.