70' 307 low compression. Need advice for next-steps
 

Hi. Long story short, my elderly mother got this car new for her 20th birthday. It's been stored since 1990. She's sick and my goal is to get it driveable within the next few months.

I towed it to my house, where i have basic tools and knowledge. I replaced: battery, starter, fuel lines and filter (drained old gas), push rods (many were bent). It will start, kind of, but not stay running and sounds like clacking from the top end (not bottom knock to my ear). The engine (and car) are completely stock with no modifications.

I compression tested the engine and once cylinder has zero compression and another 40. The rest have 110-130. This is after I replaced then bent push rods and adjusted valve lash multiple times to try to get it all to spec.

Because push rods were bent, I am wondering if I should pull the heads next and inspect. I am hoping it is the top-end so I can throw on some used heads just to get it driveable.

My problem is that I have no idea what heads will match after googling. Sounds like 350 will technically work, but provide low compression. It sounds like I need to know the specs of the heads, and I don't know what to look for while browsing facebook marketplace or craigslist. That said, it might be "easier" just to pull the entire engine and drop in a 350 or similar?

I am hoping someone here could help me get pointed in the right direction. I do know that I want to keep the numbers matching 307, even if out of the car. I'm not so sure throwing in a 350 would be "easier" or meet my timeline and skills. The car is bone stock and never touched, so I kind of wanted to keep it original, I have heard the 307 is an "anchor" and everyone I see seems to say to ditch it. But, the goal is not to be fast, I think it's be original and simple as possible.

Sounds like the timing chain has jumped,hopefully there's not a hole in a piston from a valve hitting it.
Pushrods don't just bend without a reason,rent a borescope pull the sparkplugs and have a look in each cylinder.
It could be a number of things,possible stuck valve or lifter.
You may just need a new timing chain but I'd probably replace the cam and lifters , first look inside and see if there's any major damage in the bore.
Also look for any broken valve springs.
Do you have a repair manual and did you follow the procedure for adjusting hydraulic lifter engines?
You should do a preliminary adjustment then turn the motor over without spark plugs in to check that each valve is opening and closing as it should.
This assuming the timing chain is good,if that all looks good start it and adjust them with the motor running as per the manual.
You should have oiled the cylinders before starting after sitting that long as well,I usually let them soak a couple days.

Thanks for the response @Y2Keglide!

The family story is that the timing chain broke, my dad replaced it, and it ran and drove, but it "missed" a bit and was stored ever since. In the late 90s, it ran well enough to drive a few miles when we moved (my dad said it sounded like it missed, but it ran and idled).

Before I started, I poured MMO down the spark plug holes and let it sit for a few days before hand turning it. It did turn over by hand without any noises, so I continued.

My local Autozone, O'Rileys, etc. do not seem to rent borescopes, I called. There's some on Amazon starting at $40, maybe I will do that...

I am also thinking a stuck valve or lifter. Is there a way to tell if a valve or lifter is stuck? I have the valve covers off now, it doesn't appear any of the springs are broken. The engine will kind of start, if I give it a lot of throttle, but it's way off and clacking and doesn't sound good.

I do have a Haynes repair manual. I did my best to get it to TDC, adjusted valves as per manual, turned it over 360deg, then did the other valves. I'm not sure I did it correct, but I did check push rod up and down slop several times after attempting to start. After each start attempt, I made sure each rod did not have any up/down play but was also not so tight that it didn't twist. Basically, for each rod, I did 1/2 turn on the nut after just not having any up/down play on the arm. The engine does not run or idle, so I can't adjust while running.

One thing I did not do. I didn't pull all the plugs and actually look at the rockers and springs to see if each moved. Should I do that before buying a borescope? Or, any other suggestions?

Thank you! I appreciate it!

Yes with the plugs out spin it over either buy hand or with the starter motor.
A remote starter switch that hooks to the solenoid is handy but if not available maybe someone can turn it over with the key while you watch.
Given the story it sounds like dad replaced the timing chain but didn't address a bunch of bent pushrods from when it broke and the chain may be off the mark so that should be checked.
I assume you know what cylinder has no compression so when you watch the rockers I'd start with that one.

Just to add in.

Plus one on getting the cheap bore scope and plus one on verifying CAM timing. I could be installed wrong or defective and it jumped again. Some of the 307's have a plastic coating on the gears. If that broke off and fell in the pan the gear would look good and someone may have just done the chain. If that was the case the first time the motor decelerated hard it would jump timing again.

Miss adjusted valves is one of the most common issue with new mechanics and first time engine builders. I have seen a few times guys that rebuilt the whole motor and called me cause they could not get it started. Almost every time it ends up being valves too tight or too loose. If its not that it is the distributer not in right or a firing order issue.

There is a leak down tester that can show you where the compression leak is. You can borrow them and at a chain store and watch some youtube video on how to use them. You will need a air compressor, you do not need a big one. You can also just hook a air hose up to a spark adapter and blow air into the cylinder If you loosen the rockers on the cylinder it should hold pressure, You should hear air from either the carb the exhaust or the oil cap.

(If your heads have issues)
With a stock 307 and no other performance parts I would be tempted to just run the heads to the machine shop and have then gone over. You buy a set a flee market heads you could in the the same situation. First find a decent Machine shop, second talk to them and let them know you just want a working set of heads if it comes to that. You an always just get a quote. This biggest pain about removing heads is the exhaust manifold bolts. Some may break off. Then they will need extracted.

There is a way to check Cam timing with out pulling anything but the valve cover. It is not super accurate but you should be able to see 5-7 degrees error. Only issue is I use a dial indicator to do it.

Thanks for the replies.

Unfortunately, the borescope shows a damaged piston on the cylinder with 0 compression (trying to upload a photo here). I agree the timing was off so much at some point that it likely damaged the pistons, valves, etc. I think this confirms that the whole engine needs to come out. I could not really maneuver the scope towards the top of the cylinder to check the valves, but after I saw he damage to the piston, I just stopped because I knew at that point the whole engine needed a rebuild (I think, anyway).

I think I either need to pull and rebuild the original 307 (likely $2-3k), or buy another sbc engine to swap in as-is (which is another risk). It's the worst possible scenario for this situation, but it is what it is.

I would be grateful to hear any advice you guys may have. I really did want get it running, as my mom is sick, but it doesn't appear likely at this point. It may be worth spending $2-3k now to then sell later, but I don't know if rebuilding the original 307 (to keep the entire call all-original) is worth it, or if rebuilding a donor 350 would actually be more desirable to a buyer later. Or, perhaps just sell the whole lot now and let the next person deal with it (and maybe promise a ride when complete).

Thanks again.
https://cimg8.ibsrv.net/gimg/camarof...1bf3b829d3.jpg

That's if the 307 is even rebuildable.
I don't know that having the numbers matching engine is really much of a plus with a 307.
If I was a buyer I'd much rather have a 350,a new crate engine would be a big plus IMO.
Here's a really nice kit that will avoid hassles like getting the carb rebuilt etc.
Comes with a nice intake and carb,the whole shooting match and will bolt right in replacing that anemic 307 with much better performance and still very reliable.
It will also look great when you open the hood.;)
https://www.jegs.com/i/ATK+Engines/0...aAlqMEALw_wcB#


https://cimg8.ibsrv.net/gimg/camarof...61d3f313f8.jpg

If it was me I would keep the original engine even if you do not repair it. I agree that right now a number matching 307 is not a big money vs a non-number matching but I also thing giving the next guy a the option of returning to original could be a good selling point 10 -15 years from now. Certainly, worth not sending it in as a core.

One thing I have seen, guys with small blocks upgrading to a LSx motors selling their low miles small block. I cannot believe how pricey the crate motors have gotten. I am guessing they are not selling anywhere near as many as they use to. Which brings us to another point. Are you sure want to get another Gen 1 small block. The LS is a really strong motor. They tend not to wear out the cylinders like an old school small block. You can take a 6.0 out of a truck, with a 150,000 miles on it and just put rings, bearings, oil pump new rod bolts and a aftermarket cam. Now you at 450HP in an engine that can handle 600+ hp and will hold together at 6500 RPMs. You can do the whole project for around $1,200
How to Swap in a Carb-Equipped LS Engine (motortrend.com)

The two major reasons to go with the LS design motor is one: the heads. The way the heads where designed the is a lot of room to grow but even the stock heads on a 6.0 are decent up to 500 HP. The second reason if the Y shape block with 6 bolt mains. The block itself can support over 1000 HP.

Thanks for the advice.

The 350 Jegs crate motor sounds like a good option, but is a little too pricey for me (works out to about $3,500 shipped)

An LSx also seems like it could be a option, but with the mounts, oil pan, exhaust system, trans adapter, and carb conversion might be about the same price.

I am curious. What about a used engine? For example, a 350 with compression #'s and warranty from a junk yard? For example, I see a "350ci" from a "88-94 Silverado" locally for about $800. I do understand I cannot compare this to a rebuilt engine, but it may suit my purpose to be able to get the car running, driving, and get to a place I can store it long term. Mainly, I do not know what years 350 carbureted motors will drop-in without modification.

Could another option just be any other 350 (in my case, a documented "good" condition with warranty)? Does it need to be a carbureted version only, or will my current intake and carb be swapped? And, what years will drop-in without modification? I noticed, for example, the alternator is on the opposite side. I assume I just need to swap my brackets and pulleys onto the new engine?

Thanks so much for your support!

I think about any 1st gen 350 will bolt in from 1967- early 1990's but not too sure the later ones will take your manual fuel pump and the 307 carb will be a dud on a 350.
If you can find a deal on a complete carbed 350 it should be an easy swap.
That Jegs engine has everything you need carb to pan gaskets valve covers and all and has an HEI dist.
It may be more than you want to spend but in the long run can save you a lot of headaches run great and be very reliable.
There are cheaper long block (with heads) engines available but you'll still need to deal with intake,carb,dist. and only the dist. off your 305 would work right on a 350 and even that is likely a points unit not the more desirable HEI.
Use engines are a crapshoot,most junkyard warranties are only 30 days and that doesn't cover the labor you'd be out if you get a failure.
Then you have to pull it back out and reinstall another used one,that's the risk you take.
If it was my project I'd bite the bullet go with the crate engine,clean up the engine bay and repaint then install the new one.