JDIllon

Hi Guys, the engine has a lifter that turned sideways. Probably from over reving during a downshift. That is the good and bad news, the bad, it ruined the cam. The good is that the block, crank and the rest of the motor is fine. Didn't even hurt the lifter bore. I was planning on rebuilding this fall so we are going to go thru the engine now and freshen everything up including pistons. I think it was lucky that I heard a noise in cylinder #3 when letting the engine cool down in the pits. It was #3 intake lifter. JD

John Shiels

Lucky man

SouthernSon

That is good to hear Jim. My second engine build this year seems to be doing pretty well, too. The first blow up not so lucky. Maybe we can keep them together for awhile.

dvandentop

jim what kinda noise was it making?

wow so the rollers on the lifter was running the opposite direction of the roll of the cam lobe? crazy stuff

i am sure you had a beer when ya found out wasnt anything worse! i am happy for ya too!

Short-Throw

Jim,

Class act!

I've been there and done that! :o

Glad you clarified and ended any speculation. It won't be long before you're posting more videos driving past everybody!


Mike

dfinke23

How does that happen? Kind of like valve float?

0Randy@DRM

It's better to be lucky then good sometimes

Randy

RX-Ben

Anyone know why lifters turn? I had this happen on an engine once, I could not find even a guess as to why it happens.

Bink

Abrupt change in cam speed (over-rev)...bounced the lifter off the lobe.

sothpaw2

This happened on a downshift? Can anyone clarify for me how to downshift safely? My instructor at NCM was critical of my downshifts in that I was doing more of a "blip" in his words and not fully matching the revs. It sounds like if you go too far you blow the engine. I don't expect to get it just right even half the time--so am I supposed to err on the high side or the low side????

Andy

davidfarmer

I think Jim is referring to mechanically over-revving, not just a bad "blip". In other words letting the clutch out too soon and the tires dragging the engine to 8000rpm or more. Shifting into 1st instead of 3rd can do the same thing. NOT saying that is what happened, but it's about the only way engine revs can get high enough to wreak that kind of havoc.

Still odd the lifter can turn. I assume the LS7 has the retainers like the earlier engine. I assume the lifter must have destroyed the retainer in the process???

GM had a batch of engines in 01' that had bad retainers in them.....one hole was rotated around 10º off axis. I had two good race engines ruined by this issue. No directly related to Jim's problem, but worth sharing. Inspecting your retainers thoroughly is worth the effort!

Katech_Zach

This would happen during a downshift when you mechanically over-rev the engine. When you mechanically over-rev the engine you shift into a gear that is too low for the speed of the vehicle. The drivetrain motors the engine beyond redline and there is nothing the ECU can do to limit it. It's very stressful on valvetrain and any reciprocating components for that matter. We've finished races with over-revved engines, but they are always rebuilt immediately after or a failure is almost guaranteed.

When you're blipping the throttle, you're inputting the desired engine speed via throttle position, and if you accidentally blip it too high the ECU has the ability to limit that input (unlike a mechanical over-rev). Blipping too high is not going to cause immediate failures, but over time blipping off the rev limiter is going to be harder on equipment. What you want to do is get much of your braking done early, then focus on your downshifting. Don't use the engine to slow down the car immediately in the braking zone. This will be easier on your equipment and you'll be able to better focus on the downshifting. If feel that you don't need to push it so hard in an HPDE. It's not a race, you're there to learn. As you get better and better, you'll brake closer and closer to the limit of the car in the braking zone and that compressed braking distance will require the downshifting to be done in that shorter period of time, but this is a skill developed over a long period of time. That's what makes the pros the pros.

When I heard of the lifter spinning, I took a closer look at the video posted in this thread (http://forums.corvetteforum.com/auto...vir-video.html). Something caught my eye, so I downloaded and went frame-by-frame. The photo captured below speaks for itself.

Katech_Zach

A lifter can turn when the valvetrain goes out of control.

Exactly.


When it goes out of control, the lifter is lofting over the nose of the cam. We can measure this on our Optron Valvetrain Dynamics test cell. An electric motor turns over a "buck". It's a block with a hole cut in the side. There is a dummy crank, no bobweights, no connecting rods, and no pistons. An electric motor drives the engine and spins the valvetrain. A laser is pointed at the valves via the hole in the side of the buck. The movements of the valves are plotted out on a graph and we can measure loft and bounce. Rev limit on the cell is 12,000rpm. We design packages to have a margin of safety above the set redline, but no margin is 8000, or 9000+rpm on any of our LS7 packages.

Here is a video of a recent valvetrain test for Motus Motorcycles' Katech KMV4 direct injected engine.

0Randy@DRM

Number 10s

Painrace

Man, I am glad that is all it was, Jim. Very good catch and very good ears or did you feel you had over revved it? Anyone who starts getting to the limits has done it. You sure had that car going.

When do you get it back together?

Good info Jason. Your young eyes are a lot better than mine.

Jim, was this going down the front straight and into turn one?

Jim

sothpaw2

[QUOTE=Katech_Jason;1574714416]This would happen during a downshift when you mechanically over-rev the engine.

When you're blipping the throttle, you're inputting the desired engine speed via throttle position, and if you accidentally blip it too high the ECU has the ability to limit that input (unlike a mechanical over-rev). Blipping too high is not going to cause immediate failures, but over time blipping off the rev limiter is going to be harder on equipment. What you want to do is get much of your braking done early, then focus on your downshifting.>

Thanks Jason! Glad to know too much blip is not the end of the world. I have been braking harder earlier in the zone to get most of it done, then doing the shift at the end. That's easy in T1 at VIR but I can't do it going down from 130 to 70mph turn in at the end of the back straight. In my video, it's about a 2-3 sec braking zone. I never put the clutch in below 100 mph (I'll be going to 3rd with redline at about 100mph) so that way I can't possibly mechanically over-rev. I want to do ALL the mechanics of the shift below 100mph.

Andy

shifter77

Get her done

davidfarmer

I saw that in the video too, but didn't go back for analysis. I caution people that down shifting "through the gears" increases the opportunity for this to happen.... Synchros were invented for a reason, and I find it best to do a single shift (5th to 3rd directly for instance), and not let the clutch out until the last second before turning.

Just my opinion, many drivers like running through the gears, but I prefer to focus on braking 100%, then grab the gear and clutch at the end.

bowtiguy

looks like link bar morels are in your future....

but then again maybe that pulls the weak link out of the equation and it could have been much worse..

Bink

Cool video.

I can see the loft. Is there a little bounce going on at the higher rev range??