13 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHEvidence of valve-piston hit
Reported or suspected cause
lifter " pumping up "
Reported cause
No successful repair reported for this finding.
1
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0
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Reported cause
I have seen that many times....A broken spring will cause low compression...The contact is due to the lifter " pumping up " from oil pressure, without enough spring pressure to keep it at spec height..
Leading evidence: 'lifter " pumping up "' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'lifter " pumping up "' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Inspect valve spring' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed
The reason why I brought this up was that I recently troubleshot and repaired the same issue you have.
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Suspected cause · Original poster
Probably a dumb question but so far y'all haven't clobbered me for my other dumb questions
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Suggestion
Inspect the valve spring for that valve, I am curious if it is broken.
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Suggestion
Personally I would replace the valve spring, make sure the valves are sealing, re-install the engine, then do a " running assessment" on it.....
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Suggestion
Of course you don't " have" to put the engine back in the car if you already have a Run Stand or DynoCell, you could have it running in about 2.5 hours, but you have no such equipment ..
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lifter " pumping up "
No successful repair reported for this finding.
1
Identified cause
0
Suspected cause
0
Reported fixes
Read evidence and context
Discussions that report identifying a cause
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Reported cause
I have seen that many times....A broken spring will cause low compression...The contact is due to the lifter " pumping up " from oil pressure, without enough spring pressure to keep it at spec height..
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
13 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
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Generation: 20261026T144035Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
Back in January (yes 8 months ago), after failing to diagnose the dead engine myself I took it to my indy who diagnosed no compression on C4, 85% on C5. I've finally gotten down to see those cylinders and valves. The first thing I noticed was a really sloppy job of applying loctite or whatever they used on the valve cover - I was not the first person to be in there. There was loctite around the valve cover bolts when I pulled them out... Anyway - once I got down to the valves, the first thing I noticed was that all valve lifters (intake and exhaust) for cyl 4-6 were in the "up" position in the sense that I could grab them without a suction cup - all except one. That one, the first one on the intake side of C4, was down maybe 3 mm or so compared to the others. Clue #1.
Then I got down to the valves and piston heads. Clear contact in the photos below. I'm just sharing. Now I get to shop around for a new engine block.
Cyl 4 piston head - evidence of contact
Cyl 4-6
Valves for Cyl 4-6, with damaged valve circled
I have seen that many times....A broken spring will cause low compression...The contact is due to the lifter " pumping up " from oil pressure, without enough spring pressure to keep it at spec height..
The contact on the piston head is most likely not enough to effect performance.....Most of the time you can simply replaced the valve spring ( even without removing the cylinder head ) and restored full function ...
But you do you .... A fresh rebuild never hurts anything (except your wallet) ...
When I say I have seen it many times, it doesn't mean it is "common".. Failure Analysis has been my forte for 50 years, so I have seen a lot of all failures... ( and enough of broken valve springs to say it is not "rare" or "common on M96 engines, but is rarer than most failures.)
I can't say that there is a markable difference in durability between .1 and .2 springs, but in general, the spring tension and tensile strength determines the likelihood of spring failure....The higher the tension/tensile strength of the spring is more likely it is to fail , and the lower the tension/tensile strength the less likely it is to fail....Ie, ... the higher performance the engine, the more likely it is to have a spring break......and the lower the performance ( think stationary industrial engines ) the less likely ( and rare ) it is to have valve spring breakage....
The .1 and .2 springs are not a lot different in tension/tensile strength ..
because thats what everybody says. Porschetech above was the first to suggest otherwise. Contact to piston head can travel through arms to crankcase and cause damage and balance issues that i cannot see...
Sorry this happened to you. The reason why I brought this up was that I recently troubleshot and repaired the same issue you have. Don't know if you had seen that thread. I am not sure what your symptoms were, but if it was really just misfires and no compression, you might of been able to save it with a new spring. Hope it works out well!
Looking at your picture again, it appears the valve with the broken spring was most likely rotating around and kissing the piston. It was essentially floating.
https://rennlist.com/forums/996-foru...hlight=misfire
Think about it /look at it like this .....
The valve stem is only 6mm od, they bend very easily on impact with the piston.....Yours doesn't even appear to be bent ( just shinny).
Nothing else in the engine is as fragile as the valve stem, not the piston, rod, crankshaft ect .....I"m not sure what your advisors are worried about.
Like I said Failure Analysis has been my forte for 50 years and that includes collateral damage/chain-reaction damage...
Spending $20k for Insurance for a $20K problem that may not even exist, doesn't sound like getting your money's worth to me ..
Now if you want to do upgrades while doing an engine rebuild/refresh, that's a different scenario..( if you got the disposable cash )
Personally I would replace the valve spring, make sure the valves are sealing, re-install the engine, then do a " running assessment" on it..... Then if the assessment shows it needs to be rebuilt, then OK.
I and my wallet like where this is going. Question that's been on my mind this whole time - to reassess the engine, or do a running assessment as you say, the engine has to be in the car, with oil, coolant, wiring harness hooked back up etc? Probably a dumb question but so far y'all haven't clobbered me for my other dumb questions
Yes, putting the engine back in the car is the fastest, least expensive way to assess the engine, takes about 4 hours.........Then drive it as long as it takes to assess.
Of course you don't " have" to put the engine back in the car if you already have a Run Stand or DynoCell, you could have it running in about 2.5 hours, but you have no such equipment ..
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