I over revved the engine an now it does not run well

[marty77]

Today was my first day taking out my 1978 PRS Club Ford 1600. As I was going through a chicane the throttle stuck wide open and revved to the moon. At least 7000+ RPM for a few seconds before I realized what was going on and was able to turn it off and safely pull over. In the pits I found a broken zip tie had gotten stuck under the pedal stop and was holding the throttle cable tight, I went back out and the car ran poorly. It would rev cleanly for a few thousand rpms between 4-5000 but not always. It was not consistent as to which gear or throttle position it would rev cleanly. It felt like the equivalent of the car on the rev limiter or a bad set of plugs. I would never run cleanly below 4000 rpm or above 5000 rpm

Any suggestion on where to start? I was thinking plugs but I am not sure how an over rev would have fouled the plugs

A friend suggested I may have skipped a tooth on the timing. Is there a manual out there that shows how to reset the timing set?

Also, how much advance do we run with these cars and what rpm do you all shift gears?

Thanks
Marty

[E1pix]

Smarter heads aplenty here, so mind wide open if I’m wrong... but I’d think the last thing I’d personally do on any engine that runs poorly after an overrev is to rev it.

First thing I’d suspect is a bent valve, and a compression test might be the best starting point without potential, further damage. Not sure about spark plugs being a factor here, if it ran clean and well before.

Sorry to hear, and best of luck in it being an easy fix.

Edit:
And, Oh, you might drain the oil and look at it in the sun or strong light... and pray for no hint of “metalflake” in the oil.

[marty77]

Good call on a comp test or leak down. That would be wiser than to start tearing it down blindly.

Is there a service manual for these engines if I do need to tear it down to swap valves?

In the pits after the over rev, it revved cleanly. So I thought maybe I got away with it. Under load is when it started running poorly. I pulled in after that. Now that I am remembering, when I pulled the clutch after I had it under load, the car wanted to stall unless I gave it some gas to keep it going. I'm not sure if that symptom muddies the water or not, just thought I would put it out there as another symptom

[stonebridge20]

Pull the valve cover and see if you have excessive valve lash. If you have bent exhaust valves and most likely you do, the valve won't close all the way and you'll get larger than normal valve clearance between the valve tip and rocker.
Intake .008
Exhaust. 018
Is roughly what should be normal clearance.

[Earley Motorsports]

Like above and what Stonebridge says. I would also check for a bent pushrod or two. Once again a rattling tappet/rocker would indicate which one it is. Best of luck.

[E1pix]

I don’t know if you can idle a Kent with the valve cover off, but I have done that with a flat-4 and valve motion variances become clear.

If compression and leakdown are good, and you have no obvious or clattery valve noises, and clean-looking oil, your friend’s thought of changed timing may well be valid.

Disclaimer: My IQ matches Margot Robbie’s age, so reader beware...

PS — We live on the road now but are 43-year Lakewood residents. If local help is needed, JD McDermott is a great guy if still in biz (Front Range Motorsports)

[Speedy_Farmer]

I would Contact Pete Christensen @ Total Precision Engines in Ft Collins, (970)797-0712 or cell# 970 631-5610 he is a great person and the knowledge
He could diagnose the problem it for you, and has all the supply's to fix it. He's the Frist person I would use to rebuild it also.

Allen

[marty77]

Thanks for all of the info! I am hoping to get the car out of the trailer and up onto the lift in the next few days to how bad of a mess I made

[Offcamber1]

Thanks for all of the info! I am hoping to get the car out of the trailer and up onto the lift in the next few days to how bad of a mess I made

1. as previously noted, check compression

2. as suggested, check lift at the rocker arms with a dial indicator. (If this was a new motor it is really easy to wipe a new camshaft on a lobe or two. this would show up in the compression check.)

3. if it is intermittent, particularly once warmed up, check ignition. If P&C system, gap points and replace condenser. An intermittent problem is almost always ignition. If electronic ignition, borrow someones spare pertronix unit and see if it goes away. If still persists, replace ignition wires regardless of type of ignition.

4. If problem is there when warmed up, also possible head gasket issue so do #1 with the donk warmed up.

a 7k over rev would lead me to worry more about the bottom end as that is where expensive stuff happens.

Smarter folks here will suggest more, no doubt.

Edit: one more thing related to #3: replace spark plugs. Years ago I had rebuilt my brother's FF donk and had all kinds of trouble getting it to run, went down the cam timing bunny trail. only to find I had 3 out of 4 BAD tested champion racing plugs. That was 40 years ago and to this day I have never purchased or used another champion spark plug.

[marty77]

Pull the valve cover and see if you have excessive valve lash. If you have bent exhaust valves and most likely you do, the valve won't close all the way and you'll get larger than normal valve clearance between the valve tip and rocker.
Intake .008
Exhaust. 018
Is roughly what should be normal clearance.

Are these clearances hot or cold? I saw on Pegasus Tech sheet has some specs for hot but a cold spec would be nice so I don't have to fire it up again and cause more issues

[racingflyboy]

Valve clearance Cold: .005 Intake, .010 Exhaust. I'd guess bent valves due to over rev, but it could be worse. A compression or leakdown test will help indicate if it valves. I second Speedy Farmer's advice to take it to Pete at Total Precision Engines. Pete is great, builds great (legal) engines. Has all the right equipment and parts, etc.

JD McDermott retired, closed up shop and moved to Idaho back in about '17(?) or so.

Good luck, best wishes.

Steve

[stonebridge20]

Are these clearances hot or cold? I saw on Pegasus Tech sheet has some specs for hot but a cold spec would be nice so I don't have to fire it up again and cause more issues

That's a hot spec but cold, they should be very close to those specs.
This is just to start you on the diagnosis path.
If you'd like, post up what clearances you came up with cold here and we can go from there.

[E1pix]

JD McDermott retired, closed up shop and moved to Idaho back in about '17(?)

Good to know, Thanks.

[marty77]

I finally got a chance to open the car up and here is what I found.

-This was my first time running the car and the over rev happened on the first lap I ever drove it. I had double checked all of the chassis bolts but never looked at the carb bolts. I pulled the air cleaner and saw the top of the carb (the part that holds the floats) was about 1/4" loose and the jet in the middle of the carv body was almost all of the way out. Pretty sure that is my rough running issue. Lesson learned on being more thorough

- I did a leak down and all of the cyls seem good. 2 had 0% leakage and 2 had 10% leakage past the rings

- When I checked valve lash, I used 2 different methods and got 2 slightly different results. Both methods were done cold. When I checked lash by fully depressing #1 valve and check #8 valve, I got ~.002 tighter measurement than checking valve lash on the base circle of the cam. As in check valve lash with both valves closed and at TDC on the compression stroke. Does that seem normal? It seems like the #1/#8 lash method seems to be the most common way to adjust.

-All of my valves were ~.005-.007 loose

- Is it okay to set lash cold? I had heard add .002 to the hot spec if you want to set lash cold. Does anyone have experience setting lash cold?

Thanks for all of the feedback!

[marty77]

Valve clearance Cold: .005 Intake, .010 Exhaust. I'd guess bent valves due to over rev, but it could be worse. A compression or leakdown test will help indicate if it valves. I second Speedy Farmer's advice to take it to Pete at Total Precision Engines. Pete is great, builds great (legal) engines. Has all the right equipment and parts, etc.

JD McDermott retired, closed up shop and moved to Idaho back in about '17(?) or so.

Good luck, best wishes.

Steve

I just saw this as I was re reading the thread. Interesting the cold spec is tighter. I guess in my head I would have thought the cold spec would have been looser because the metal would expand and close the distance. I am guessing that it is the opposite logic, as a whole the engine expands and loosens up as it gets warm?

[TimH]

- Is it okay to set lash cold? I had heard add .002 to the hot spec if you want to set lash cold. Does anyone have experience setting lash cold?

https://iveyengines.com/faq/

[E1pix]

That’s some great info, pretty cool of Jay to post that.

Glad the leakdown’s not worse! Hope you nail it so you can hear it make noise.

[jrh3]

Of course it’s going to run crappy with the top of the carb about to fall off. Fortunately no fire.
Bet it runs fine now

[stonebridge20]

Of course it’s going to run crappy with the top of the carb about to fall off. Fortunately no fire.
Bet it runs fine now

This ^

[marty77]

https://iveyengines.com/faq/

I have an aluminum head btw. On the vey page when it gives cold, then hot lash spec. Below it says to "not to re torque" what is it referring to? I was told the lash adjuster didn't have a lock nut, it's just the threads were intentionally deformed to hold the adjustment setting

[stonebridge20]

I have an aluminum head btw. On the vey page when it gives cold, then hot lash spec. Below it says to "not to re torque" what is it referring to? I was told the lash adjuster didn't have a lock nut, it's just the threads were intentionally deformed to hold the adjustment setting

Don't re torque the cylinder head.

[E1pix]

For fear of breakage if already at full torque?

[DaveW]

For fear of breakage if already at full torque?

My guess is you don't want the aluminum head too firmly attached to the steel block. Too much tension might restrict it from expanding (different thermal-expansion coefficients) with heat and cause issues.

[Hawke]

And if you are concerned about over revving. Two suggestions. Fit a good quality rev limiter. Pertronix works for me, and it's set at 7,200. But wire it with a microswitch to disconnect it if it fails.

Also, the rev limiter wont help if you hit the wrong gear. A tip I got from an Australian Formula Ford champion has worked for me for many years. When changing gears in the 3-4 plane, keep your thumb down, and keep your palm on the left side of the shifter. In the 1-2 plane, thumb up and keep the palm to the right. In the last 25 of racing, I've never picked the wrong gear.

[DaveW]

...Also, the rev limiter wont help if you hit the wrong gear. A tip I got from an Australian Formula Ford champion has worked for me for many years. When changing gears in or into the 3-4 plane, keep your thumb down, and keep your palm on the left side of the shifter. In or into the 1-2 plane, thumb up and keep the palm to the right. In the last 25 of racing, I've never picked the wrong gear.

That's what I do.

[E1pix]

My guess is you don't want the aluminum head too firmly attached to the steel block. Too much tension might restrict it from expanding (different thermal-expansion coefficients) with heat and cause issues.

Thanks, good info, guess I was wondering if it *ever* loses torque (from stretch( for example), and if there’s a need to check after lots of miles.

Is it okay to check later at, say, an 80-90% value? I did that on my kart heads when dead cold, if only just to feel better. ;-)

[TimH]

Also, the rev limiter wont help if you hit the wrong gear. A tip I got from an Australian Formula Ford champion has worked for me for many years. When changing gears in the 3-4 plane, keep your thumb down, and keep your palm on the left side of the shifter. In the 1-2 plane, thumb up and keep the palm to the right. In the last 25 of racing, I've never picked the wrong gear.

Key points.

[Roland V. Johnson]

If you keep torqueing an Aluminium head when it is hot , it will just keep squashing down. When installing the head, Spray both sides of the head gasket with Copper Coat and torque it down. Making sure the oil feed hole to the head is on the right front as the gasket is on the block. Set the valve lash cold @ .006 In and .015 Ex and check when the engine is HOT (best when you just come off the track) .010 In and .020 Ex. (It is usually pretty close if you set it properly in the first place.) Hot adjustment is always fun if you have an over the valve cover exhaust system. The rocker adjusters are self locking and should have resistance to turning. If they do not, call Ivey and get new parts.
P.S I never re-torque aluminum heads until I pull them off and have them freshened, but I do check the valve lash now and then. If you want to check the head again cold you can always set the torque wrench to 60 #'s and check if you want.

[alangbaker]

I just saw this as I was re reading the thread. Interesting the cold spec is tighter. I guess in my head I would have thought the cold spec would have been looser because the metal would expand and close the distance. I am guessing that it is the opposite logic, as a whole the engine expands and loosens up as it gets warm?

All the dimensions get larger when something gets hot...

...including the clearances between objects.

The only exception would be when there are different materials involved. A gap between a steel part and an aluminum one might get smaller with heat due to the difference in thermal expansion between the two metals.

All the parts in an FF Kent valve train are steel, so the pushrod gets longer, but the block gets taller as well.