Lost compression - need ideas

[fishinman78]

Push rods too long??

How did you establish pushrod length?

 

[B RON CO]

Hi, a lot to the story.
Were the bores honed fine and smooth for moly rings?
Were the rings end gap checked and filed?
Did the rings fit properly in the grooves?
Are you positive the rings are not upside down?
Are the lifters properly adjusted?
Was your engine loaded with engine pre lube?

A real leakdown test is a long process, each cylinder at TDC compression stroke.

A compression test is quicker.

I would make sure the valve adjustment is "loose" and do a compression test.
My first impression is your shop does not see any easy way and is not interested in your project.
Good luck

 

[centex77]

Push rods too long??

How did you establish pushrod length?

With an adjustable push rod.

Hi, a lot to the story.
Were the bores honed fine and smooth for moly rings?
Were the rings end gap checked and filed?
Did the rings fit properly in the grooves?
Are you positive the rings are not upside down?
Are the lifters properly adjusted?
Was your engine loaded with engine pre lube?

A real leakdown test is a long process, each cylinder at TDC compression stroke.

A compression test is quicker.

I would make sure the valve adjustment is "loose" and do a compression test.
My first impression is your shop does not see any easy way and is not interested in your project.
Good luck

I can't remember what the finish was. It's been 4 years.

Rings were checked and filed by myself and brother in law. Gaps were oriented at 180 apart.

Rings fit into the grooves just fine from what I remember. Don't remember any binding or tightness when assembling.

From what my memory serves the rings are right side up. They had a marking on them.

Lifters are hydraulic rollers. We haven't done any adjustment to them.

Engine was loaded to the gills with pre assembly lube. I got made fun of for how much I went through.

I have a feeling this was the shop saying they are done with this project and to move on. We've been pretty hard on them on price to this point ($17,500 spent to date with them) so I'm certain they are looking to recoup some cost. I get it. They didn't build the engine so they don't know what they are getting in to and don't want to screw with it anymore.

Sent from my Pixel 3 using Tapatalk

 

[Matlock]

Price isn't too far out of line....
Pull engine, rebuild, reinstall, tune, warranty their work
and deliver to customer in a timely manner.
They are in business to make money.

 

[gnpenning]

Ignorant question but what would the fuel and ignition systems have to do with it?

Shop performed a leak down test while hot and it came back as 30-40% on all cylinders.

Sent from my Pixel 3 using Tapatalk

To make sure all your "scattering" isn't only compression related. You also mentioned worrying about washing the cylinders. Yes you need to find the low compression issue first.

 

[centex77]

Ok. This thing has some issues.

First - Checked compression and whether cold or hot the compression was between 120-130 on all cylinders.

Second - The coil is arcing BAD. It's arcing to the negative terminal on it through the boot and electrical tape we wrapped around it. It's a bright ass red and purple arc.

Third - It's running so rich it's literally puffing black smoke at idle. This plug is after 6 miles of driving and it was brand new.

Fourth - We checked the lash on the valves and that seems good.

Fifth - The vac pump they told us they put on it isn't there so it's no wonder our brakes suck.

We poured some oil in a cylinder when it was cold and compression jumped from 120 to 150-160. So the rings aren't out of the question but I'm thinking they just need to break in.

But until I get the carb tuned and coil to stop arcing I'm not going to be able to really break this motor in. Anything above 2500-3000 and it starts popping and missing bad.

Sent from my Pixel 3 using Tapatalk

 

[36Fan]

What do you mean by custom carburetor?

 

[centex77]

It's a Holley double pumper that the shop tweaked. That's all I can tell you because that's all they told me.

Sent from my Pixel 3 using Tapatalk

 

[gr8scott]

Trick Flow Twisted Wedge aluminum heads that have been CNC ported 66cc chambers

Your signature says AFR heads. Either way they're aluminum.

Your double pumper carburetor might be way too big for a 302.

 

[centex77]

My bad. On the sig.

What's odd is we had an Edelbrock 500 4 barrel on here originally. Shop told us it wasn't flowing enough air and the motor would die out around 4000rpm. I'm ignorant on carbs so I took their word for it.

Sent from my Pixel 3 using Tapatalk

 

[centex77]

They put a Holley 4150HP on here.

1977 Ford Bronco/Fiberglass Body/302 bored .030/balanced/Twisted Wedge aluminum heads/cam/5spd/Locked w/ 4.10’s/35” BFG/4” suspension/3” body

 

[Broncobowsher]

Can you get a bore scope? Take a peak in a cylinder. See if there is a mark on the piston where the valve was smacking it.

You mentioned they did a leak down test and were getting 40%, with that much leakage you should be able to hear air leaking out someplace. In this case I suspect intake or exhaust, possibly valve cover. Intake or exhaust is a valve problem. Valve cover is a piston/ring problem.

This is one of those where the engine just needs to come out (after the leakdown test and peak through a plug hole) and have a good tear down and going through. It helps to diagnose what you will be looking for before you tear into it.

The breaking up above 4000 RPM may have been the valves floating and not a caburator issue. Trying to drive through it may have put the valves into the pistons. In which case the valve springs were wrong.

You might even find something weird like a total junk timing chain or the dowel at the front of the cam went bad. But no matter what, with what you stated for leakdown, the engine is coming out and coming apart.

 

[centex77]

Well that's what the shop said. They also said compression was 70-90psi hot and we've tested it at 120 hot or cold. The crank case is full of fuel and it's running so rich it's puffing black smoke out at idle. The coil is arcing across itself while it's running. Plugs are going completely black in 5 miles and stinks of fuel. I think their "custom carb" is flooding the engine and washing the cylinders down.

All that said, I'll get a bore scope and take a look.

1977 Ford Bronco/Fiberglass Body/302 bored .030/balanced/Twisted Wedge aluminum heads/cam/5spd/Locked w/ 4.10’s/35” BFG/4” suspension/3” body

 

[oldiron]

It's a Holley double pumper that the shop tweaked. That's all I can tell you because that's all they told me.

Sent from my Pixel 3 using Tapatalk

What cfm double pumper? It's always been my experience that on a ford small block bigger is rarely (if ever) better. Do you have access to an "off the shelf" 600 cfm vac secondary carb? Probably still too large but might tame your super rich condition. My guess is that if you cure the coil arc over problem and use a reasonable carb, most of your issues will be solved.
Greg

 

[centex77]

It's a Holley 4150hp. I just bought an Edelbrock 750cfm. Should be here in an hour.


We checked the float levels on the Holley and the rear float was screwed so far down that it wasn't able to be adjusted with the nut and it's still pouring fuel out of the sight bowl. Fuel pressure is also at 9psi. We spoke to the shop and they are bringing out a new carb, coil, coil wire, and plugs to the house today.



1977 Ford Bronco/Fiberglass Body/302 bored .030/balanced/Twisted Wedge aluminum heads/cam/5spd/Locked w/ 4.10’s/35” BFG/4” suspension/3” body

 

[oldiron]

750 cfm is great for an all out high rpm race car. Horrible in a small block powered, heavy bronco. Almost impossible to tune at idle, off idle transition bog is terrible. If you want to experiment yourself...try both like I did, the 750 will be almost undriveable and you'll still be stuck with an over rich condition. Think about it this way.....you're gonna spend 99% of the time driving in the 1200-4000 rpm range and maybe 1% in higher ranges and even then only for a few seconds. Run the numbers for cfm requirements to suit where the engine spends most of it's time. Small cfm carbs (350-600) offer better throttle response crisper acceleration and more stable idle characteristics. The smaller ones (350) will however "fall off" at higher revs (over 6k). If your mud-bogging or dune racing....750 cfm MAYBE. If you plan on driving on the street 600 cfm vacuum secondary MAX.
Hope this helps.
Greg

 

[Timmy390]

As said 750 is BIG. I run a 770 on my built 390FE.

My advice is to verify the valves and pushrods are not bent before throwing more money in carbs and such. Depending on how much valve to piston clearance there was the tight valves could have done damage not to mention burning a valve. I know a burnt valve that quick is unlikely but it's possible if the were hammering it.

Tim

 

[DirtDonk]

did you guys note the cam specs? That's a REALLY BIG CAM for a 302.
So with that cam, I would not think a properly tuned 750 is as far out of line as we would normally think. Might still be wrong, and it is still a small engine, but it's still a really big cam.
And all on a dual-plane intake. Sounds like a classic case of at least slightly mis-matched parts. If the intake is a higher-rpm, higher-rise design, being a dual-plane is not a deal-breaker (that's a lot of hyphens!), but it's still a big cam.

Were the valve springs on the head to begin with, or did they come with the recommendation of the cam manufacturer?

Is there a mechanical pump in use, or is it electric? Gas in the oil is a bad pump more often than it is overly rich jetting I think. But if you've got gas in the oil to any great extent and it's not a mechanical pump, then that secondary gas-dump issue really was a doozy.

Gas pressure at 9psi and a carburetor? Yeah, get a regulator on that puppy and dial it back to less than 6. Personally even with a performance build I'd start at 4-5 psi maybe. You need volume of course, but it's still a carburetor so you don't want too much pressure.
A full bypass system might not be a bad idea to add to your future list-of-things-to-do on this rig.

Are you running a PCV system? Or just valve cover breathers on both sides? Even with an engine with that much cam you probably should try to fit a PCV system to the engine. Especially given the current conditions it might come in handy.
What distributor? Vacuum advance or not? Unless you're going to just be racing this Bronco, I would run a vacuum advance.

Hopefully it's just something like springs or pushrods. But it sounds like you might be dealing with more than one issue. Which is actually kind of common with new full builds.
And with the issue others are having with roller lifters failing we can't ignore that either. Have you seen the thread or two on the flat rollers?
What brand are your lifters? And the cam?

Paul

 

[centex77]

I swapped out to a 600cfm Edelbrock. Haven't installed it yet.

No vacuum advance or choke on the carb.

We installed a regulator and dropped the pressure on it down to 6psi. It's a Holley Red electric pump.

Shop came out and swapped out one of the bowls that the float adjustment was maxed out on and done wrong and brought a new coil and a new coil wire.

Just using a single valve cover breather for now.

We popped the intake manifold and all lifters are pumped up and working. Pushrods are straight. Valve lash is good.

We are changing the oil out.

I'm starting to reassemble the thing and see what happens.

1977 Ford Bronco/Fiberglass Body/302 bored .030/balanced/Twisted Wedge aluminum heads/cam/5spd/Locked w/ 4.10’s/35” BFG/4” suspension/3” body

 

[oldiron]

Well, how'd it go?