Cracked spark plug porcelain-timing?

[sms986]

As part of my restoration, I am getting the engine ready to put back in (1989 alpha 1 5.0 with a 5.7 shortblock swapped in) and I started it up for the first time in 3 years yesterday. Stupid me cut the starter wire in the dash to get it separated years ago, and while digging to find out why it wasn't doing anything I noticed cracked porcelain on one of my plugs. Further inspection showed that the neighboring plugs were also cracked. One of them had a chunk of porcelain missing.

I've read and read and everyone seems to say that cracked porcelain is usually due to being rough on the plugs when installing. I will go ahead and say now that I've never ever cracked a plug installing it or taking it out, and I've had to pull plugs from unpleasant motors with an impact before. Not saying it isn't possible, but I think it's pretty unlikely that 3 plugs are cracked from installing. I put these ones in with a torque wrench and a plug socket.

I haven't yet looked at the rest, but I'm curious as to what might cause this. The engine seemed to run fine the few times I had the boat out years ago and it started and ran fine last night. I have done a lot of motors in the past but to be honest this is the first time I have ever built one with timing that I had to set through a distributor. Could I be cracking the porcelain from detonation? I set the initial idle timing at 12 degrees BTDC. This was the best idle I got and it was recommended to me by a guy who builds sprint car engines. After setting the idle timing, I didn't do anything.

 

[alldodge]

Could be the plugs had a factory defect, don't know but its very unusual for it to crack on its own

Setting timing 4* further advance then spec may work out, but I wouldn't even try it without a working knock sensor.

 

[Scott06]

Normally with detonation you will see specks of metal aluminum from the pistons on the insulator. if they are present likely detonation is happening

i wouldn't add initial timing. Boats are under different loads and more detonation prone than other motorsports, hence marine applications use way less advance than a typical automotive application. If it wont idle well at factory timing setting adding 4 degrees is only curing another issue like ignition or carb issues.

 

[Scott Danforth]

loose spark plugs would prevent proper heat sinking and the plugs get hot, cracking the porcelain

 

[jhande]

What year is that 350 cu.in.?

Does it have a points distributor or HMI?

If it has points, properly adjust them first.

Timing, use a timing light and a vacuum gauge off the intake. Set timing to factory specs (unless you have a beefier cam) with the light and then slowly turn distributor to get the vacuum as high as you can at idle (20-22).

Usually the only issues I've come across for broken porcelain on the outer side of plugs: is extreme heat or something some how knocked into them. Make sure you are using the proper plugs for the motor, properly gaped and if they came with copper washers use them.

 

[sms986]

I believe it's HEI. Has a separate coil. The only thing used from the 350 was the shortblock-rotating assembly and the block. Everything else, including heads and cam are from the old 305.

What is the correct timing? I don't have any vacuum gear but I have a timing light.

 

[sms986]

 

[alldodge]

The old 305 is a non-vortec motor and timing will be at 8* BTDC
The plugs were the wrong ones and should be MR43T which are marine type

 

[Scott Danforth]

if the new 5.7 is a vortec, your plugs are way too short.

 

[jhande]

You have a separate coil so it's not HEI, take the distributor cap off and you'll see points.

350 bottom end with a 305 top end, to bad you couldn't have the 350 top end.

Timing - you're going to see with the timing light at idle with vacuum advance disconnected should be between 8-12 degrees BTDC. Were ever the motor idles the smoothest.

How does the spark plug boots look?
Is there heat shields around the plugs?
The spark plugs actually look to me that they got broken either installing or removing.

 

[Scott Danforth]

I believe it's HEI. Has a separate coil. The only thing used from the 350 was the shortblock-rotating assembly and the block. Everything else, including heads and cam are from the old 305.

What is the correct timing? I don't have any vacuum gear but I have a timing light.

wait a minute.....back the truck up.

generally stock 305 heads have too small of valves for a 350 and have too small a combustion chamber to run on pump gas without the motor detonating like teenager boys at their first peep show.

what head casting do you have? very specific.

if you have heads 14093627, your combustion chamber size is near 52cc

many 305 combustion chambers are in the 54ish CC range vs the 5.7 in the 76 for smog motors and 64cc for vortec/LT/Gen1 performance, etc.

running 305 heads on a 350 may have pushed your CR up in the 11:1 to 11.5:1 range without the ability to breath due to the small valves.

small valves and small combustion chambers on pump gas under constant load which would mean you are running lean, eating your pistons, and running hot.

 

[poconojoe]

This has gotten interesting. I would like to follow....

One question, probably irrelevant, but why are those spark plugs so rusty? I thought you installed new ones. I don't think my old plugs looked anywhere near that bad. And I have no idea when the previous owner changed them...

 

[Grub54891]

Quote: Timing - you're going to see with the timing light at idle with "vacuum advance disconnected" should be between 8-12 degrees BTDC. Were ever the motor idles the smoothest. Unquote.
Marine distributors don't have vaccume advance. If it does, it has the wrong dizzy in it, not marine rated.

 

[sms986]

Ok, so plugs are rusty because even they came from the 305. Pretty dumb not to replace them when I built it, but hey, that's way in the past. They were a little rusty on the outside but in good shape when put in. I know, I know I didn't get so lucky to have broken 8 plugs in a row on this engine. Like I said, I've never broken a plug. I can see if I busted one putting it in, but all 8?

Leaning towards detonation. Now I don't want to say that none of you know what you're talking about here, cause it sounds like you are on the right track with the heads. The guy who got me the shortblock (non-vortec) is an engine builder, and a very good one. He saw the 305 and all, took a quick look at everything, and said the 350 will work fine with all of the 305 parts. Maybe he overlooked it? The motor ran just fine. I heard no abnormal pinging or anything, but it did have one issue the 3 times I took it out. It would get hot. I would have a hard time getting it to start again after running it for a while. If I pulled the filter off I would see a bunch of white vapor in the carb. I suspected vapor lock, rebuilt the carb and put in a spacer. Haven't started it since then, until now. I'll see if I can get the casting number off the heads tomorrow. If I have to replace heads, no big deal.

I've worked on tons of 2 strokes and built a few car motors, but all of the 4 strokes had a computer and such. Never had to deal with this and I never do much with chevy engines, so I'll need some help finding the right stuff. Truthfully, I have no clue what I'm doing with the 305-350 swapping around, but I had good faith in that guy.

 

[poconojoe]

Ok, so plugs are rusty because even they came from the 305. Pretty dumb not to replace them when I built it, but hey, that's way in the past. They were a little rusty on the outside but in good shape when put in. I know, I know I didn't get so lucky to have broken 8 plugs in a row on this engine. Like I said, I've never broken a plug. I can see if I busted one putting it in, but all 8?

Leaning towards detonation. Now I don't want to say that none of you know what you're talking about here, cause it sounds like you are on the right track with the heads. The guy who got me the shortblock (non-vortec) is an engine builder, and a very good one. He saw the 305 and all, took a quick look at everything, and said the 350 will work fine with all of the 305 parts. Maybe he overlooked it? The motor ran just fine. I heard no abnormal pinging or anything, but it did have one issue the 3 times I took it out. It would get hot. I would have a hard time getting it to start again after running it for a while. If I pulled the filter off I would see a bunch of white vapor in the carb. I suspected vapor lock, rebuilt the carb and put in a spacer. Haven't started it since then, until now. I'll see if I can get the casting number off the heads tomorrow. If I have to replace heads, no big deal.

I've worked on tons of 2 strokes and built a few car motors, but all of the 4 strokes had a computer and such. Never had to deal with this and I never do much with chevy engines, so I'll need some help finding the right stuff. Truthfully, I have no clue what I'm doing with the 305-350 swapping around, but I had good faith in that guy.

Maybe the guy meant all the accessories would work. Maybe he wasn't referring to the heads? Miscommunication?

 

[sms986]

Eh, I got bored.

Cylinder head casting # is 14101081. 58cc chamber. Oops.

Block is #14093638.

I'm gonna go ahead and find some other heads now.

I'm not sure what he meant. I recall asking about the heads and reading mixed reviews between them working fine and them bumping the CR too high. Paid a total of $100 to rebuild it so no big deal and no regrets (I worked for the guy in high school doing valve jobs and head rebuilds in high school so he gave me a lot of freebies.)

Now, is the intake manifold interchangeable? Or are the runners too small? I know the Qjet is good.

 

[sms986]

Pulled it all apart tonight and got everything cleaned up. Ready for new heads. Inside still looks brand new.

Is anyone able to help me out with a casting number for the heads I need?

What about intake manifold? Will the 305 manifold work?

 

[Scott06]

305 and 350 intakes are the Same. cant help you with casting numbers but you could at this point upgrade to newer vortec heads and gain about 30-40 hp. You also need a vortec intake as they have a different bolt pattern but i think worth if you need heads anyways.
these guys have a couple of non vortec and vortec heads on this page

OEM - Cylinder Heads - Marine Parts & Accessories - Products

www.michiganmotorz.com

they also sell intakes if you go the vortec route

 

[alldodge]

Hey @Scott Danforth to the front office please

 

[kvkon]

Were the plugs in the heads when the exhaust manifolds were installed?