Compression Readings All over..... What did I do :-(

[Don S]

Re: Compression Readings All over..... What did I do :-(

I could be wrong but I am thinking a bad/burnt exhaust valve cold potentially suck water it on the intake stroke. This would also account for my dead cylinders and low compression

On 6 out of 8 cylinders? All at the same time?

 

[HVAC Cruiser]

Re: Compression Readings All over..... What did I do :-(

On 6 out of 8 cylinders? All at the same time?

I know, that's what has me baffled All at once.. thats why I am thinking they just never checked the valves and they were bad to begine with

.

 

[Don S]

Re: Compression Readings All over..... What did I do :-(

I know, that's what has me baffled All at once.. thats why I am thinking they just never checked the valves and they were bad to begine with

.

If they were bad to start with, it wouldn't have run ok when new. But the running, then (let set for a while and rust) then repeat as necessary will keep causing more problems.
We can't see what you see on your engine, only what you type. So we (I) ask a lot of questions.

 

[Bt Doctur]

Re: Compression Readings All over..... What did I do :-(

Very similiar to a motor I built. 6 hrs breakin time by the owner so I gave the ok to power up. First time was spitting , sputtering and 45psi in two cylinders. Found all the oil washed off the cylinder walls, 6 leaking intakes(acetone test) and 4 exaust valves leaking.(Acetone test) No carbon at all in the motor. Spark plugs were a cement color.I suspect it was run on more ethanol than gas.Reseatd the valves. Drained tank and refilled with new, test ran on a 6 gal tank mixed with 1/2 pint of outboard oil.Perfect performance. What color are you spark plugs, what was found around the spark plug area in the combustion areas?

 

[Alpheus]

Re: Compression Readings All over..... What did I do :-(

Did you degree the cam at all or did you just line up the dots?

You do the leakdown and I betcha your going to hear air coming out of your carb and your exhaust...

 

[HVAC Cruiser]

Re: Compression Readings All over..... What did I do :-(

Hi Don,
I know you ask questions to help figure it out, and I appreciate all your help.

The engine still sounds like she is purring like a kitten thats what throws me she runs smooth as silk.
Here is a little clip

[/URL][/IMG]

The audio is a little bit off she sounds tinny on my cheep camera but its not in person.

The engine always ran smooth, but I have always had a power problem. I 1st figured I was over propped then the carb etc... always gave a problem going over 4500 1st I figured I was over propped then I figured the carb, because I new it was bad. The old Q-jet was sucking air at the throttle shaft and would not take adjustment.

Yep I did degree the cam, I don't trust the dots I think your right
tomorrow I am going to do a leak down on her to try to get closer to the root of the problem.

 

[HVAC Cruiser]

Re: Compression Readings All over..... What did I do :-(

Hi Boat Doc,
I haven't pulled the heads yet but the plugs had some carbon, I was figuring the moly rings didn't fully seat yet. None of the plugs were fouled out.

For fuel all I use is Mobil premium, I don't run that oxygenated or 20% ethanol crap. I am a bit worried that the bad carb washed the walls BUT what throws me off is squirting oil into the chamber doesn't change the reading

 

[sstocker31]

Re: Compression Readings All over..... What did I do :-(

Did you wire the throttle wide open when doing the compression tests??

 

[Aloysius]

Re: Compression Readings All over..... What did I do :-(

Moly faced rings seat immediately. If the ring lands weren't taped off during bead blasting, they can be damaged.

A leakdown test will tell where it's leaking. Everything else is idle speculation.

 

[HVAC Cruiser]

Re: Compression Readings All over..... What did I do :-(

Good Morning everyone,

Yep, the throttle was WOT dung testing

The guy that did the blasting and machine work used to be pretty good, I just happened to be lucky enough to get him when he was in a very bad way, His 4 yo grandson had just been murdered weeks earlier and he was not in the right frame of mind.

After I finish feeding breakfast to the kids I am going to go out and do a leak down, and hopefully put this mystery to rest.

I am really hoping its the heads, don't really want to pull the engine again

 

[HVAC Cruiser]

Re: Compression Readings All over..... What did I do :-(

Well, all the speculating is over. Its both the heads and a piston
Every low cylinder had either a leaky intake or exhaust valve, mostly intake.

Cylinder #1 blew a piston

Thanks to everyone for all your help and input. I already have the motor ready to come out. Right now I am just to upset and frustrated to set up my gantry

 

[coheej]

Re: Compression Readings All over..... What did I do :-(

As you're tearing it apart, you might check to see what the ring gap was. If it was too tight it will break ring lands. Also, you might recalculate your compresion ratio. With a leaky throttle shaft, you may have been running lean enough to detonate which will break ring lands.

As someone else mentioned, maybe the bead blast was too agressive.

 

[Ursula]

Re: Compression Readings All over..... What did I do :-(

Sorry Bill....I feel your pain.

 

[Alpheus]

Re: Compression Readings All over..... What did I do :-(

I cant believe that engine sounded that good and looks like that on the inside.

Did it have any vibrations at all?

 

[HVAC Cruiser]

Re: Compression Readings All over..... What did I do :-(

Thanks everyone,

The ring end gap was on the money I used a file set. The rings didn't break, top rings were at .018 2nd ring was at .020.

As you're tearing it apart, you might check to see what the ring gap was. If it was too tight it will break ring lands. Also, you might recalculate your compresion ratio. With a leaky throttle shaft, you may have been running lean enough to detonate which will break ring lands.

As someone else mentioned, maybe the bead blast was too agressive.

The detonation is what I feel what happened The engine leaned out at 4500 detonated, and broke the ring land. The pistons were old trw2256f I believe. They were forged slugs but now their junk. My guess is the shrapnel went through the engine and messed up the valves.

Looking at the pistons the one that broke is melted, the others show signs of detonation.

I already started shopping for parts. Seeing its closed cooling Im thinking of going with the Edelbrock performer or E-Street 70cc aluminum heads & one of my pals gave me a set of new KB134 +7cc pistons he had sitting around .

The bad side, I called Jack Merkel ( talked to his son) to have him do the bore and deck work. I am sorry to say Jacks wife died over the weekend so everything is on hold till next week. My heart goes out to them, she was a very nice woman.

I am thinking that after I get her back together I am going to rent some time and get her broken in on the dyno before I put her back in the boat. This is the last time I want to be doing this, I am not leaving anything to chance. If its going to blow up this time I rather it be in the shop Not to mention I am curious to see real #'s on its performance

EDIT-

Hi Al

Me neither she sounded great here is another video

 

[Aloysius]

Re: Compression Readings All over..... What did I do :-(

Did that ring come out of that hole, or another one??

 

[HVAC Cruiser]

Re: Compression Readings All over..... What did I do :-(

Did that ring come out of that hole, or another one??

It coming from another hole would be a neat trick I would have a lot more problems .

It didn't totally grenade, only partial thank God . Luckily it only messed the block up a little at where the ridge normally is, no cylinder wall scoring if you can believe that I am hoping to get away with a .030 over and deck the block.

Another thing on my side is this block has never been bored or decked even though its 1970 4 bolt main and has had hot rod builds done to her before.

Also most all the metal melted to the top of the piston, I think that is what really saved me

 

[coheej]

Re: Compression Readings All over..... What did I do :-(

Another thing on my side is this block has never been bored or decked even though its 1970 4 bolt main and has had hot rod builds done to her before.

You previously said you had a deck height of .016" and you were running a cr of about 9.4 -1. You were doing this with a Speed Pro L2256F forged piston and it probably detonated and broke the piston. Now you're going to deck the block a little and go to a KB134 hypereutectic piston; on a motor that's going to be seeing 3500 - 4500 + rpm most of the time, I think you need to use a forged dish piston or go to a .060 - .070" mls head gasket.

 

[HVAC Cruiser]

Re: Compression Readings All over..... What did I do :-(

You previously said you had a deck height of .016" and you were running a cr of about 9.4 -1. You were doing this with a Speed Pro L2256F forged piston and it probably detonated and broke the piston. Now you're going to deck the block a little and go to a KB134 hypereutectic piston; on a motor that's going to be seeing 3500 - 4500 + rpm most of the time, I think you need to use a forged dish piston or go to a .060 - .070" mls head gasket.

Hi coheej,

I think it was a comedy of errors , although not really funny .
10:1 on 92-93 octane pump gas should be fine. I have only myself to blame for what happened I went against my better judgment.
Here is what I feel were the contributing factors

1) old pistons from the 70's, I saw what I thought were burn marks in the ring land area, was told no worries I wanted to believe :redface:
2) Original carb would not take adjustment at all ( at the time I didn't have the money for a new one
3) because the carb wouldn't adjust I couldn't get it to idle properly, would barely run below 800rpm ( after the electronic advance kicked in I timed it the best I could. Turns out it was at about 11-12 deg initial advance.

Run engine at WOT, engine leans out, timing too advanced tears off top of piston at weakest point.

I do have a few choices to try to keep compression below 10:1. Right now I am arguing between if it better to run a dish with a 64cc head or a flat with a heavy gasket like you said and a 70cc and or forgo decking it.

The only thing is with going to aluminum heads I would really like to deck the block for the best mating surface possible.

Any thoughts???

 

[coheej]

Re: Compression Readings All over..... What did I do :-(

Hi coheej,

I think it was a comedy of errors , although not really funny .
10:1 on 92-93 octane pump gas should be fine. I have only myself to blame for what happened I went against my better judgment.
Here is what I feel were the contributing factors

1) old pistons from the 70's, I saw what I thought were burn marks in the ring land area, was told no worries I wanted to believe :redface:
2) Original carb would not take adjustment at all ( at the time I didn't have the money for a new one
3) because the carb wouldn't adjust I couldn't get it to idle properly, would barely run below 800rpm ( after the electronic advance kicked in I timed it the best I could. Turns out it was at about 11-12 deg initial advance.

Run engine at WOT, engine leans out, timing too advanced tears off top of piston at weakest point.

I do have a few choices to try to keep compression below 10:1. Right now I am arguing between if it better to run a dish with a 64cc head or a flat with a heavy gasket like you said and a 70cc and or forgo decking it.

The only thing is with going to aluminum heads I would really like to deck the block for the best mating surface possible.

Any thoughts???

Running a dished piston on a 64cc head will be almost the same as running a flat top piston on the 70 cc head. Personally, I'd run the dished piston on the 70 cc head and get my compression down to about 9.2 - 1 for safety.

The aluminum heads will help with that also. Because they will dissapate heat better, I usually tell my customers in car applications that they can run about 1/2 of a compression point higher with no problems.

If the block is fairly square to begin with (and it should be), you should be able to deck it for a new sealing surface. If the machinist takes care in leveling the block to his machine, he shouldn't have to remove more than .002" -.003" unless the block is twisted. If he has to remove .005", that will decrease your combustion area by about 1 cc.

Also, the KB134 piston will require a little larger ring gap on the top ring.