Have you seen my missing cylinder? SBC compression all over the map!

[FishNinJay]

I'm wondering how bad this is...

I have a '71 FJ40 with a 327cid SBC. Rebuilt cylinder heads, unknown type, but the engine itself might be from '65 vette originally. Has an automatic transmission conversion also. Starts and runs Ok, but idles a bit rough. Has Edelbrock 4bbl 1406 carburetor.

Finally found some time to work.. and got some new toys from Summit. Put in AutoMeter 2" tach, and vac gauges.

At idle, my RPMs are around 400-600. The vacuum flickers rapidly back and forth between 13-15 In-Hg. Interestingly, when I push the gas, the vacuum seems to go up to like 24-30 In-Hg, then drops down to under 10 momentarily then back to baseline. Isn't it reverse, and vac supposed to drop with rapid accel and release?

So I hooked up my new timing light, and the RPMs seem to correlate reasonably well with the AutoMeter gauge. There's a Mr. Gasket timing plate and a white line mark. But, I can't get a steady reading at all, at any RPM .. the mark is jumping all over the place! I disconnected & plugged the vacuum line to the distributor vac advance. But, no knocks or pings either. I recently replaced the spark plugs, rotor and cap, but re-used the same GM HEI, spark plug wires/boots.

Awhile few weeks ago, a local mechanic did a quick test.. I think it was called a "snap KV" or just "KV", and he said something was wrong with my #4 cylinder. My #4 was "down"?? I haven't found much info on this KV test here or on Google, .. but it sounded similar to compression?

Today, I checked my compression, and the numbers worry me. They aren't supposed to differ by more than 10-15% cylinder-to-cylinder, and mine are all over the map! #4 is definitely messed up!

<front, driver-side=<

130 <-[1] [2]-> 155
99-100 <-[3] [4]-> 25-28
93-95 <-[5] [6]-> 122-125
158 <-[7] [8]-> 159-160

Firing order: 18436572

Here are some blurry quick photos of the spark plugs also. They only have about 120 miles of mixed road/highway use on them.

(sorry about the OOF cr@ppy photos.. handheld, dirty hands, and hot in my garage!)

So if only 5 of my cylinders are over 100, I guess I'm actually driving a V5 FJ40?

So, I didn't squirt any oil down and retest, because (1) I didn't have any oil handy, and (2) which cylinders, and what's the point?

Do I need a leak-down test?

If it's still running ok, what's the danger in still driving it? Where is this heading? Any chance of an easier fix? Valves? Rebuild or install a new crate? I'm inclined to get a new crate over rebuild, but wondering if I can put it off for awhile. Also, not quite sure what to order, and how to get it swapped in there? I can take more pics of the engine bay, and transmission areas. Have no idea what transmission is in there. There was a power steering upgrade, and front disc brake upgrade done. I've read that swapping an already installed SBC with a new crate SBC engine is easy? True?

Ok.. thanks for any advice and tips. Anyone local to me that could help me with this?

 

[dgangle]

Plugs: #4 looks like it's burning a little oil and that is a low compression number. I'd redo it. How is overall oil consumption and blowby into PCV valve?

Timing light jumping around: Sounds like your light is bad, bad ground/positive or the inductive pick up is not picking up spark reliably. be sure to be on # 1 cylinder, close to the plug.

Timing tab: I have seen great variations in these, especially when they are aftermarket. Best way is to use a degree wheel to verify TDC mark on the harmonic balancer and it's associated point on the tab. Make a new line if needed, bend the tab or replace it with the right one if wrong. Time for total advance of 34-38*. Read post 5 of this thread for a good explanation http://www.hotrodders.com/forum/350-chevy-timing-78715.html or do your own Froogle search for "total advance Chevrolet". That got me eleventy billion hits.

Vacuum: http://www.users.bigpond.com/ergoff/vac1.htm Sounds like you may have bad rings, leaky valve or worn valve guides. A leakdown test could tell you what you probably already know.

New/rebuild? It all comes down to what you want, afford and who you know. If it were me I'd have that 327 rebuilt as they are hard to find and have a certain amount of coolness to them that I just like. Plus they are a good compromise of power and economy comparing say a 350 to a 305. If you don't personally know someone who can rebuild it, ask around. Visit your local speed shop and see who can do this for you locally. Unless someone just totally screws you, this will be by far the less expensive option. "Crate motor" is one of the most overused and misunderstood terms going. Does one really need a 400-something HP GM performance...blah, blah, blah.

The worse thing that could happen is the engine grenades and you don't have a rebuildable core. While possible, it is somewhat unlikely. It will just keep losing power and using more oil until you decide to do something about it or not. I would just drive it and not worry that the sky is falling.

 

[cmiller114]

Overall your plugs look OK with the exception of #4...which looks like oil fouling...oil fouling in a SBC is valve guides 95% of the time. That also kills compression on that cylinder and gives a "twichy" vacuum reading. Next is a burnt valve, then the valve drops off into the cylinder.....then your done.
Do the compression test several times and get an average. A squirt of oil in each cylinder will give a better reading on the valves.
Jumpy timing can be, 1) bad light 2)bad #1 wire 3) worn out distributor and/or cam gear 4) worn out timing chain.
A snap KV=Snapon KV meter. It tests the voltage firing from the coil to each cylinder. A low reading on any one cylinder points to a problem there without really diagnosing the problem....could be as simple as a bad plug wire.

The port on the front passenger side of the carb is for the vacuum advance. The port on the drivers side is manifold vacuum and your gauge should be connected there. The center, large port is connected to the PCV on the valve cover and to what else?

IMHO you bought yourself a tired old motor. It may run another 100k as is and it may grenade tommorrow. Keep your RPMs low and don't tow anything....blue smoke will be the final note.

No way to judge on a rebuild without pulling the motor apart. If it's a pristine 327 (I doubt it) then by all means rebuild! If it's been bored on honed to the limits, it's an anchor. Anything in between is a judgement call.

It's getting hard to find good mechanics for a rebuild because GM crate motors are so good and cheap.

 

[FishNinJay]

That's all awesome info.. I love this site!
Very good links too!

These compression numbers were an average, over 3 cranks. They were pretty close together.

The timing light pick-up was placed on the #1 wire, but close to the cap. I'll try it again near the plug.

Right now, my vac gauge has a nylon line going to a vac tubing coming off the engine heading down towards the passenger side transmission area. I'll try reconnecting it to the carb port you described. For some reason, this morning, there is a concerning hissing noise I hear.. and the vac gauge reading lower. I think I somehow created a vac leak somewhere..

Re.. oil. Remarkably, it runs pretty good. Seems to have decent response and pick-up. No oil drip, and level still looks full and clean on the dipstick. The oil pressure is kind of low, when engine hot. Temps run 190-205 steady. Maybe creeps up a bit to 210 in very slow hot LA traffic. But, my oil pressure is around 5psi! On cold start, it's 40, then declines. While driving, the psi climbs to around 20. I've been told/read that this oil pressure is pretty common in these SBCs, or.. too low and need a high-volume pump, or.. harbinger of doom?

Yeah, I kind of like what I've read about the 327, and it seems cool that it was originally a '65 Vette! But, if it's time, it's time.

For marital harmony sake, I need to have this rig reliable and not constantly being wrenched on by me or a local mechanic. So, that may tip me over towards replacing it with a new engine. We'll see.. one thing is for sure.. even if I replace with new, for sure something else will pop up on these rigs!

Thanks again for all your advice, knowledge, and encouragment!
For now, I'm content to take your advice and just drive it, and not worry about the sky falling (even if it is ).
- Jay, aka "Chicken Little"

 

[dgangle]

...I need to have this rig reliable and not constantly being wrenched on by me or a local mechanic.....

WAKEUP! you will give up, run out of $$ or both before that ever happens. It's a 40 year old vehicle that has been customized. You better be handy, have money and a desire to keep it going or there will be another one given away on craigslist.

 

[FishNinJay]

WAKEUP! you will give up, run out of $$ or both before that ever happens. It's a 40 year old vehicle that has been customized. You better be handy, have money and a desire to keep it going or there will be another one given away on craigslist.

.. one thing is for sure.. even if I replace with new, for sure something else will pop up on these rigs!

yes.. I know..

 

[cmiller114]

For marital harmony sake, I need to have this rig reliable and not constantly being wrenched on by me or a local mechanic.

You're a funny guy!

 

[ken_79-fj40]

WAKEUP! you will give up, run out of $$ or both before that ever happens. It's a 40 year old vehicle that has been customized. You better be handy, have money and a desire to keep it going or there will be another one given away on craigslist.

Very true. I've been wrenching on mine for almost 10 years now and although it's currently quite reliable there's always something that needs attention. As for the motor if it's still running decent and isn't smoking I would run it. My original 2F burned oil from the day I bought the truck but it wasn't until it began to blow lots of smoke last year that I dug into the motor.

 

[ducktapeguy]

For marital harmony sake, I need to have this rig reliable and not constantly being wrenched on by me or a local mechanic.

Start looking for a good divorce lawyer.

But seriously, as long as it's running and it isn't your only car (you do have a real car that you can actually drive, right?), I wouldn't worry too much. Just take things one step at a time or else you'll start to feel overwhelmed. I know when I first got mine I felt like everything needed to be done at once. But just try and concentrate on one item at a time, it can even just be little things like checking for loose bolts or changing the oil. Eventually you'll start to see some progress.

 

[cruiserbrett]

I think the KV test is a spark analizer that is like an oscilloscope with all the spark bursts shown. poor compression affects the voltage of the spark spike, and consquently it will show up as different than others.

Spark scatter is likely one of three things:
Distributor: worn distributor bushings weights, bad points
Distributor drive: worn distributor gear or cam drive gear
Cam/Timing issue: sloppy timing chain, worn thrust button.

All in all, sounds like a rebuild would be best, honestly. Low oil pressure is generally indicative of worn bearings, and the low compression is just bad. might be a head gasket, but likely its just worn out rings.

 

[dargreg]

I can just make it out but I think you have double bump heads,or camel bump heads as they are sometimes called.Usually in 65 era vettes they were 2.02 intakes a very sought after head even if they are 1.94s.Unless the block is totally hammerd rebuild it there is not many out there.

 

[cmiller114]

Is this tool what was used for a KV?

Ignition troubleshooting - Snap-on DIS/kV Ignition Probe

Dargreg is 100% correct about camel hump heads. If you can hookup with a guy doing a resto and looking for a period correct engine.....corvette or camaro, he may be willing to trade you a crate motor for it. Look on the front part of the head. If you see a raised area that looks like this:

====.............====
=====...........=====
=================
==================

you have the high performance "camel hump" heads. Pull a valve cover, write down and photo the casting #s...you may have something.
Everything said previous about rebuilding it still holds true.....but it's a more valuable motor for a chevy guy than a FJ40 guy looking for reliability ...sorry, that still cracks me up.

 

[Brian in Oregon]

Let's get back to what exactly you have here.... You said rebuilt heads. Let's assume they were rebuilt correctly, and there is no valve or valve guide problem. Yet the vacuum gauge indicates possible problems with a burned valve or worn valve guide. I'm wondering if the valve might not be properly seating, perhaps from a too long push rod or hanging hydraulic lifter or maladjusted valve train, causing low compression and failure to burn oil coming past the rings (since the short block is well used)?

 

[numby]

Dargreg is 100% correct about camel hump heads. If you can hookup with a guy doing a resto and looking for a period correct engine.....corvette or camaro, he may be willing to trade you a crate motor for it. Look on the front part of the head. If you see a raised area that looks like this:

I sold a pair of heads that I was told were camel hump (didn't look right to me. I'm not real engine knowledgeable) that needed to be completely redone. That payed for a brand new set of aftermarket heads w/ stainless valves and some mild porting. I was happy and so was the other guy. Still had to cough up for the stroker rods and crank, though.

Everything said previous about rebuilding it still holds true.....but it's a more valuable motor for a chevy guy than a FJ40 guy looking for reliability ...sorry, that still cracks me up.

Your risk with the 327 is that the engine may be too old and worn to be rebuilt for the fifth time and you'll still have to get a replacement. Drive it a little longer for a better idea of what the vehicle's more pressing issues are. If addressing minor stuff like valve seals, etc don't solve the things, my temptation would be to sell it and drop in a very boring absolutely basic and reliable Goodwrench 350 kind of engine. You need to be honest with the buyer regarding compression numbers, etc, but that way it becomes someone else's informed risk.

I'm a little more sympathetic about the daily driver aspect. Just be prepared to walk, bike, hitchike, skateboard, or ride the bus for a few days every so often while you tinker.

 

[mike@dw]

Thanks for posting this thread, as I am in a similar situation with my SBC 350. Oil fouls out 2 cylinders plugs about every 1K miles. Starting to get grey smoke on start up, and if the PVC is not hooked up then also smoke from the valve covers.

I did not do the motor swap so I don't know the history. I only know that it is originally from a 71 EL Camino.

But it still runs pretty strong. My plan as of now is to let it ride until the winter when I generally don't drive it. Then look at a rebuild or a simple 350 crate motor. You can get a new motor from GM for about $1500. That is the way I am leaning as of now.

 

[FishNinJay]

Thanks for posting this thread, as I am in a similar situation with my SBC 350.
>snip<
But it still runs pretty strong. My plan as of now is to let it ride until the winter when I generally don't drive it. Then look at a rebuild or a simple 350 crate motor. You can get a new motor from GM for about $1500. That is the way I am leaning as of now.

Hi Mike..
similar.. but mine isn't really smoking bad (yet). I think mine is fine for driving around town, errands, dropping kids off at school and sports. Probably won't use it as much for my work commute, because I really can't leave myself stranded. Anyways, sounds like you and I have a similar plan.

Numby, yeah, I have no idea how many rebuilds. I figured out at least the cylinder heads were changed, because the spark plugs that match the engine stampings, don't fit! If there is any collectible value to this '65 vette engine, I wonder if it is more "sellable" now, even with it's few bad cylinders, or just drive it until it fails? Maybe later, I'll do a google search and see how many Vette-nuts are out there looking for a 1965 327cid engine!?

 

[mike@dw]

Hi Mike..
similar.. but mine isn't really smoking bad (yet). I think mine is fine for driving around town, errands, dropping kids off at school and sports. Probably won't use it as much for my work commute, because I really can't leave myself stranded. Anyways, sounds like you and I have a similar plan.

Numby, yeah, I have no idea how many rebuilds. I figured out at least the cylinder heads were changed, because the spark plugs that match the engine stampings, don't fit! If there is any collectible value to this '65 vette engine, I wonder if it is more "sellable" now, even with it's few bad cylinders, or just drive it until it fails? Maybe later, I'll do a google search and see how many Vette-nuts are out there looking for a 1965 327cid engine!?

As worn as my motor is these days, I did a 700 mile trip in the 40 a couple weekends ago. Just took a couple qts of oil with me, some spark plugs, tools, and my AAA card in-case the worse happened. Thing ran like a champ the whole way.

 

[FishNinJay]

For marital harmony sake, I need to have this rig reliable and not constantly being wrenched on by me or a local mechanic.

You're a funny guy!

"reliable" for a 38-year old rebuilt, modified, frankenstein, FJ40 means the rig isn't a permanent lawn ornament on cinder blocks

 

[dargreg]

You,ve got lots of miles yet on that one if the plugs are any indication.

 

[FishNinJay]

I'm wondering how bad this is...

<front, driver-side=<

130 <-[1] [2]-> 155
99-100 <-[3] [4]-> 25-28
93-95 <-[5] [6]-> 122-125
158 <-[7] [8]-> 159-160

Firing order: 18436572

Wow.. how time flies!?

A year has passed, and my '71 frankenstein rig is still going strong, still looking beautiful. I found an awesome local guy, retired, who does classic car restorations and mechanical work out of his garage. He's checking out my rig.

Here are current compression numbers, done about 9 months after the test I did above..

95 (1) (2) 125
80 (3) (4) 15
85 (5) (6) 110
135 (7) (8) 130

I should probably say, he used his equipment, versus me doing the test with my equipment a year ago. But the numbers seem to jive.

He did a wet test and threw some oil down.. with improvement in compression numbers from 10-20 across the board:

115 (1) (2) 135
95 (3) (4) 45
95 (5) (6) 125
150 (7) (8) 150

So, cylinder 4 is still puzzling. Why so low, yet improves +30 with oil. So, if do a valve job, it might still fail? Valve and Ring? Still probably need to eventually make decision on rebuild vs new crate.

BTW, my guy checked out the engine, and it's not the double-camel humps
BUT, it IS a 327 block from a corvette..


Anyways, for now.. I'm happy the rig is still running strong and not smoking out my neighborhood.