Hot Rods engine question, low compression

I had a motor that the rings were stuck 100% flush with the ring glands (might as well not have had rings) and the compression would come up when oil was added so I really suspect valves/timing. I would verify the timing; put the engine at TDC and make sure the balancer and the rotor are pointing in the rights spots. People always suggest jumped time but I have never heard of it actually happening. Broken belts and chains sure but never actually jumped time. Seems to me it would have to take some teeth with it.

The diluted oil sounds far fetched but I guess it is possible. Maybe throw a gauge on it and crank it over and see what your pressure looks like? I get the feeling this is cam related. It is defiantly a compression issue but why... my bet is not the rings.

EDIT: I just re-read your first post, I initially read it as came up to 30-40 psi, not came up 30-40psi. That puts rings back on the table for me. I would add a squirt or two of oil to each cylinder then try and start it, if it runs I'd keep it running as long as it will run. After a few of those if it is running okay I'd take it out for an Italian tune up.

Good luck, I am curious to the fix.

 

It's hard to believe the car ran exceptionally well directly before sitting and the no-start since you have such low compression and high levels of blow by.

How many rotations do you think the engine made on the washed down cylinders? Normal cranking speed is 100ish rpm. & Is that enough to wear the bores and rings into oblivion?

 

Still not satisfied with 'rotor movement' indicating tightness of chain...
Grab harmonic balancer with both hands, and rock the crank clockwise and counter clockwise.
An appreciable amount of 'slop' both ways will tell you if the chain is loose enough to have run over the timing sprocket.
3spd never saw an engine 'jump time'??? Lots of that with the broken plastic teeth on GMs.
There were better spots to "Rig for Silent Running"...

 

I am pretty new to this game, it just seems to come up in most of these why is my engine not running/running poorly threads and I have never seen it be the correct answer. I guess I was thinking of jumping time as the chain moving one (or more) tooth over without causing severe damage. I plastic timing gear coming apart I wouldn't classify as jumping time but as failure of the gear. For my own future diagnostic knowledge, if a plastic timing gear does loose teeth, does the motor tend to keep running after? Even if the chain still kept the cam moving, wouldn't the timing be noticeably off (line up the marks and the rotor be pointing way off)?

 

He could have washed the cylinders without destroying the rings. It takes a lot to take out a set of rings more then just cranking one trying to start it as a rule.

If it will start now that you have oiled the cylinders then drive it around and check your compression again.

 

They do jump,
1 tooth and it will run , even be drivable but shitty.
2 teeth and it will run but not much power.
3 teeth and it might fart trying to start.

Sometimes they jump and the car runs shitty till you shut it off and it jumps back then runs fine.

Nylon gears are big problems and when they go, (pictured above) they scatter shit everywhere, chains jump around. So the evidence you see is it jumped time, the cause of that would be them damn nylon timing gears. They could be fine in one position with the slack on top of the gear and a few degrees rotation and then the slop is where it makes a difference. Ever time an engine with a light and the mark is bouncing around?

The chains just stretch too, they are either new in a box or on a slope of mechanical decay headed towards failure. As they stretch the cam timing gets off and performance falters, most don't notice because its gradual. They notice of you stick a new chain on though. Ever wonder why ignition timing needed to be adjusted before computers? It's not because the dizzy moved its because the chain is stretching.

The balancer and marks are tied to the crank, as long as the balancer hasn't slipped the marks will line up at TDC. Spotting any mis location of the rotor is going to be pretty hard with your eye unless its a gross amount off.

 

Thanks 31Vicky. TB33.3, sorry for pirating your thread.

 

I'm jumping on the timing chain band wagon here. My 283 ran surprisingly well with 45lbs compression. It would still chirp the tires. Burned a crap ton of oil though and didn't like to start cold. But it still ran. Grossly retarded cam timing can show up as low compression. At this point, what have you got to loose by pulling the timing cover. If the chain looks fine, then chances are the motor is a goner. I which case it's gotta come apart anyhow.

 

i did get it to run for a short time, ran bad then died, would not start again. this was after changing the oil and filter.

the owner is a fireman, he has time and tried to get it running over the course of a few days. i have no idea how long he tried. i was told washed cylinders will wipe out rings fast.......i kinda don't believe it.

i turned the crank in both directions, rotor reacts instantly in both directions

no problem, totally on topic.

 

Well I'm not real familiar with a cylinder washout.
So I surfed other sites and guys that are. It seems to be a bigger problem when an injector sticks and deluges one cylinder. The fix they say is 2 ounces of aft, spin the engine over and let it set 24 hrs. Start it the next day. Apparently the aft does better at establishing the seal then the oil takes over.

Some guys said it's impossible to damage the ring surfaces at starter rpm, it's got to be running at 1000s of rpms. But it is possible to loose compression at false starts and the aft fix was mentioned again there as well.

Some guys have noted a 20 point loss of compression across all cyl after 100 hours of use from running excessively rich. They have some damage, new rings at a minimum.

Tommy here on the ham had a problem with One of his engines no compression I believe it was a new build. One of his friends help them get it going but I can't remember what happened. He mentioned it in a thread here .

 

thanks for all the replies.
pulling the engine in the morning, customers confidence level with this supposed "engine rebuild" by the previous owner is lower than the compression readings. out it comes and off to my engine guy.

 

How did you clean the plugs? Did you sandblast them? If you didn't sandblast there is a good chance they are shorting out no matter how well you cleaned them. Test to be sure they are firing before you junk the motor.

 

i sprayed them with carb cleaner and blew them off. i hooked them to a plug wire and grounded them, they sparked really well. this is after changing them to new ones.
the motor is going to be rebuilt, numbers matching, '69 gto judge convertible........needs to be right.

 

Yep !
No self respecting judge is allowed to have low compression

 

The Pontiac 350/400s were known for bad timing chains. I've seen them anywhere from just skipped to completely broken.

 

no shame. Even Judge Judy has had some work done

 

You totally did the right thing

 

.

So this thread is all about a post 65 car?

"the motor is going to be rebuilt, numbers matching, '69 gto judge convertible"

.


No way thats off topic.


.

 

The "car" - not the "engine tech"
If we're gonna get real sticky, every sbc 350 has got to go

 

.

This whole thread is about a 69 GTO with no compression?

Really?

" numbers matching, '69 gto judge convertible"


Numbers matching 69 400 Pontiac



"69 GTO"

.


400 Pontiac?

.

 

?

 

.


"QUOTE tb33anda3rd post 11227767 member 126584
customer calls, he can't get his car started. was running fine,
the motor is going to be rebuilt, numbers matching,
'69 gto judge convertible........needs to be right.
QUOTE"


Last week it was a "331 Stroker"

This week it's a "69 GTO"
400 pontiac

Where do you draw the line?

Is this one Ok because it's a 69 GTO with a 400 Pontiac?

.

 

I believe the engine tech is totally fine. It applies to all engines. Doesn't matter if its in an OT car or a model A on deuce rails. A lot of good suggestions I will keep in mind if I ever come across a similar situation.

 

Well somehow I haven't found the post about the car being a Goat, not that I care it is still a 4 stroke internal combustion motor.

Anyway to address a few questions, @31Vicky with a hemi I have actually seen fellas destroy fresh top ends by washing the cylinders down and cranking them dry trying to start it. Dump gas down the carb crank crank crank, well the battery is dead. Charge it and repeat.

I have also seen many a good running engine jump time when it was shut off. that seems the normal time for them to jump time. Easy way to check is to roll it up on the timing marks and take a look at the rotor, if it is not pointing to the right place it has jumped time. I have also seen engines with the timing chain so loose that it wore a hole in the timing cover and still running. Engines can be funny creatures.

I would not crank it much until I checked the obvious at this point.

 

Double check the plug wire sequence. Pontiac is 18436572 BUT COUNTERCLOCKWISE at the distributor.

 

@moefuzz, sorry if it bothers you. i did not mention the model/year until late in the thread because it did not matter. i thought the engine question applied to all engines wether on topic or not. if it was on topic do you have anything constructive to add? it turns out it isn't on topic, do you erase anything you learned from your memory? again sorry to fill your head with off topic stuff.
@treb11 the firing order was right.
by the way the engine is out, on the stand and the offending vehicle has been removed from the premises. shop is cleaned.
i looked into the fuel pump hole and can see the timing chain is tight and complete, no chips or chunks.

 

Put a Flathead in it! Or at least a Chevy

 

a chain skip or incorrect firing order would not leave decent compression on two cyls.. It would be interesting to know what the machine shop finds...but maybe you don't dare bump this thread back up later

 

The man asked an honest ? regardless if it is an off topic car. I myself am interested in the final outcome. Give it a break.

 

Soooo.... Suck, Squeeze, Bang, Blow is Off Topic?