308 Engine Over Rev

I replaced the fuel lines on my 308. It took a couple months while I took care of the other obligatory “while I’m there” stuff. Once everything was back together, made sure the car had a gallon or two of fuel, oil circulated by running the starter for 10 seconds before letting my fuel pump on (security system disengages it). Then two pumps on the throttle to the floor and a half throttle for the start. The engine sputtered a few times with this, so I repeated the procedure a total of three times, starter running about 5 seconds on each attempt. The third attempt the engine caught and reved right up to a very high rev. I don’t know how high because I wasn’t looking at the tach. I immediately had my foot off the throttle and turned off the ignition as I knew it was a stuck throttle. I put my girlfriend in the drivers seat and had her cycle the throttle several times while I watched the cable and carb linkage. It was catching at about 50-75% travel at the right rear carb linkage, so it seemed. So I put a little oil on all the linkage pivots of all four carbs and the throttle not longer stuck anywhere. Restart was uneventful, from what I can tell, and the motor idles normally.

Question: how would I know if the engine was damaged? What would I see on a running engine, if anything. Other than service the throttle cable and the carb linkages, what should be examined on the engine at the next service to assess if anything was injured? I understand that there maybe nothing to do if the engine operates normally from this point forward.

 

Low oil pressure, smoke from the exhaust. But hopefully the rev limiter cut the ignition before it went too high so you may not have a problem

 

I was the rev limiter when I cutoff the ignition...I’m pretty sure there’s no rev limiter on carb 308s unless pertronix has an integral limiter in their modules. Thanks for the reply.

 

I don't have any relevant experience with the 308, but on other engines I've dealt with, there would be no mistaking damage from over-revving. It would result in catastrophic mechanical failure. You'd know it, you'd hear it, you'd feel it. Most common damage is a valve floating and hitting a piston, which is not something you'd miss. Probably next most common is failure of water pump, oil pump, etc -- the stuff that isn't made to handle extra RPMs.

I'm not familiar with a carb 308 to know whether you can over-rev it based on a stuck carb linkage. My guess is that there are probably limits built into the linkage and or throttle to prevent so much throttle input that it would result in an over-rev, even due to a stuck linkage. High-rev, sure, but probably not over-rev.

So my completely un-expert opinion is that if the engine is running OK, not smoking, and doesn't sound like a bucket of bolts, you're probably OK. Bonus points to you for trying to cycle some oil through the engine first. That could have made a big difference in terms of minimizing wear.

 

I watched the tach on my '79 go to about 10,500 on a missed shift about 1985 or so.

It seemed like it took forever to drop down to below 7K.

No damage to the car. My heart, well i survived that, too..

Doug

 

You should be ok. You revved the engine high but didn’t over rev it. Over rev situations put the engine beyond its mechanical limits by improper downshifting. It’s ver unlikely to go beyond the mechanical limits when simply revving it with the throttle. It probably wasn’t great to rev it so high on a cold engine, but it being a one time occurrence isn’t anything I’d be too worried about.


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I have seen 10,500 once also, driving and a missed shift, into nuetral.

It blew a LOT of carbon flakes off of the vavlves, which glowed like little sprklers in the rear view miror.
No damage.

I would think a dropped valve would be the immediate sign of real damage, and a miss from the piston with a new hole in the crown.

 

Thank you all for your insights. I figured it’s hard to know for sure if anything hurt though likely not. I’ve decided to take the air box off and re-lube all my linkages and the throttle cable just to be certain this doesn’t happen while I’m driving. After a nice strong drive I should know if all’s well or not. I was so bummed when it happened. I feel better about it now. Thanks all!

 

Ferrari rods give out long before the valves float.

If a rod did not come out the side its OK. Don't worry.

Is the air box off? Stuck linkage on a carb 308 is usually a rod or bell crank getting caught on a hose clamp in the middle area or I have seen deactivated high idle devices hand up the linkage too.

Whatever caused it, FIND IT, BE 100% SURE ITS FIXED.

 

Haven’t taken the air box back off yet, but it’s coming off. The glass cars are nice because the whole rear deck comes off in a minute then the box lid and filter can come off quick right after. It’s the carb trumpets and the box base that suck to remove. I’ll definitely check the hose clamps as I put them on, so I could easily have messed the rotation up on one causing a bind. Thank you.

 

There's a few comments here about built-in protections against over revving the engine from linkage items to ignition cut outs. I'm not aware of any of these actually existing.

@Rifledriver - is there actually anything in any 308 (as delivered) that stops the engine from dangerous or disastrous engine speed?

 

When I had the Digiplex boxes rebuilt on my ‘82 308GTSi they programmed a rev limiter. When you first hit the limit it’s weird, but you get used to it….

 

I'm pretty sure there was no rev limiter on any of the carb cars.

And nothing stops an over rev resulting from downshifting into too low of a gear.

 

If it's any comfort there are plenty of YouTube videos out there where they purposely WOT a gas engine or disable the governor on a diesel to film it blowing up and you'd be surprised how long it actually takes.

 

No. None.

 

Thats not what causes overrevs.

 

You'd be surprised how little it actually takes.

 

Not sure we are on the same page here. My point was to say you can overrev going down through the gearbox as well as up. I.e. downshifting which causes a significant mismatch between engine speed and vehicle speed (like shifting into 1rst when doing 80mph) most definitely will cause a mechanical overrev with likely catastrophic consequences.

 

Just try it sometime. Can be done in racing dog box but make it happen in a sycro box. Go ahead and try. .

 

No, no, no. You are still not following me. I'm not talking about skipping gears here (which I do all the time, btw). As in my earlier example, if you were to change down from 4th to 1rst at 80mph and let out the clutch you would massively mechanically overrev the engine, causing it to self destruct and likely spinning the car. It's often called the "money shift".

 

You nailed it! Thanks so much!

Update: I got really side tracked with business, but tonight got on it. Took the rear deck off, air box off, and sure enough, not one, but TWO of the ABA clamps were rotated just wrongly such that they were catching the carb cranks on the two right side carbs. It was subtle enough that they didn’t always catch, but what a really stupid thing for me not to have paid attention to when I positioned these clamps. The good news: took about 60 seconds to fix all the clamps in that area. Then had my girlfriend cycle the throttle several times while I checked for any other concern. Car started right up like the old days with the air box off...ran it until warm then some test revs. Air box back on then deck lid followed by a 30 minute night drive in the desert! No issues. Thank you all!

Side note: I started all this as my Corona fuel pump started howling so I swapped it for the Hardi...the Hardi is a super quiet pump. Holy smokes it’s quiet! Did all my fuel lines too.