Cracked spark plug porcelain-timing?

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
34,063
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?
are you looking used or looking new?

if you are looking new. buy the new ones that have been modified for proper seals and screw in studs. thats about $900 thru GMPP. you can also get them thru Summit Racing

if you are looking for used. any good machine shop, especially ones near an oval race track will have a few sets on the shelf left over from when the vortecs were run (before the rule change allowing AFR's). those are usually $400 a set, have upgraded valve springs, screw in rocker studs, the seal work already done.
 

sms986

Petty Officer 1st Class
Joined
Sep 18, 2017
Messages
239
Plugs went in last.

I'm not looking for "cheap" necessarily, but I don't need anything special. The engine will likely not see 500 hours in the next 20 years.
 

sms986

Petty Officer 1st Class
Joined
Sep 18, 2017
Messages
239
I also forgot to mention that I have dished pistons in the 350, so my compression ratio is lower than normal. Do the mercruiser engines come with dish pistons in them? I don't remember if the old 5.0 did.
 

Scott06

Lieutenant
Joined
Apr 20, 2014
Messages
1,424
I also forgot to mention that I have dished pistons in the 350, so my compression ratio is lower than normal. Do the mercruiser engines come with dish pistons in them? I don't remember if the old 5.0 did.
GM used dished pistons on both 5.7 and 5.0 , really all their engines, so your stock compression ratio of 9.0-9.4 or so is based on stock type dished pistons. If you have a non stock dish volume that would affect compression but otherwise you should be ok.
 

sms986

Petty Officer 1st Class
Joined
Sep 18, 2017
Messages
239
Cool. Thanks a lot for all the technical advice guys. My neighbor just so happened to have a set of vortec 350's in his garage. Got them from him last night. Have to find an intake and a gasket set today and I should be able to get it back together this weekend.
 

Scott06

Lieutenant
Joined
Apr 20, 2014
Messages
1,424
Cool. Thanks a lot for all the technical advice guys. My neighbor just so happened to have a set of vortec 350's in his garage. Got them from him last night. Have to find an intake and a gasket set today and I should be able to get it back together this weekend.
Did you get the intake too? In the photo it looked like you had the pre vortec 12 bolt intake vs the 8 vertical bolt Vortec intake you need to fit vortecs. Intake gaskets are diff as well.
 

sms986

Petty Officer 1st Class
Joined
Sep 18, 2017
Messages
239
I am going to order the intake online. Couldn't find a used one
 

sms986

Petty Officer 1st Class
Joined
Sep 18, 2017
Messages
239
I'd just hate to break the bank for an intake manifold. I've gotten a few for SBF motors all $50 to $75. I do want to put together a correct engine, but I don't want or need anything special or performance wise. Just want a solid motor that runs. I can't believe I can't find a used one for under $100.
 

alldodge

Supreme Mariner
Joined
Mar 8, 2009
Messages
31,869
If your motor was closed cool you could use one from a junk yard. Open cool needs a marine intake.

Could post in the wanted section at offshore only. My guess is someone like Sick Stringer will have a few laying around
 

sms986

Petty Officer 1st Class
Joined
Sep 18, 2017
Messages
239
Why would I need a marine intake? Like what differences does it have?

By the way, heads I got from my neighbor were cracked. We're looking for another set now.
 

alldodge

Supreme Mariner
Joined
Mar 8, 2009
Messages
31,869
Why would I need a marine intake? Like what differences does it have?

If your using a cast iron intake then there is no difference. Aluminum intake has brass water jacket, otherwise it will rot out over time, even in fresh water, mo so in salt
 

sms986

Petty Officer 1st Class
Joined
Sep 18, 2017
Messages
239
Ok cool.

I planned on getting a cast iron intake anyway just because of the temp fluctuations of open cooling. Not sure if that even matters.

Holding off until I find heads. Neighbor is taking a look again tonight to see what he has. Told him either vortec or non-vortec is fine.
 

jhande

Petty Officer 2nd Class
Joined
Jun 26, 2010
Messages
134
Can't believe it's real hard finding a somewhat reasonably priced 350 top end.

Have you checked salvage yards, machine shops, craigslist, FB Market Place, any local racers, etc...?
 

tank1949

Lieutenant Junior Grade
Joined
Apr 4, 2013
Messages
1,002
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.
Yes, I have cracked them by binding them up against exhaust manifold w/o using a U joint on the end of a 5/8" deep well. Not a lot of room. I have also cracked them by getting lazy and installing exhaust manifold w/o removing plugs. Too much weight will crush plugs and you will slip!!! I later fabricated a couple of 4-6" long 3/8" studs and removed hex head. I used a cut off wheel to cut a screw driver slice so that I could screw them into block via flat head sd. I hang exhaust manifold on them and slide the manifold snug and bolt on the other 3/8" bolts.. Good luck!
 

sms986

Petty Officer 1st Class
Joined
Sep 18, 2017
Messages
239
I called the machine shop I used to work at. He is going to look this week. CL was a dud, so was FB. I could call machine shops, but I have no contacts. Buying used shelf parts from machine shops is a bit of a hit or miss process, and price depends on relationship. I really don't want to spend $400 even. I got the heads from my neighbor for $250. That's fair for a stock, used pair of heads. I can clean them up and do valves. Too bad we found they were cracked. I can't believe I haven't found several pairs yet-especially since I'm in the heart of nascar country.
 

Scott Danforth

Grumpy old guy who plays with boats
Joined
Jul 23, 2011
Messages
34,063
the pair from the machine shop should be about $400-$500 done

NASCAR has not run vortec heads.....ever.

late models and sportsman class did for a while prior to the rule change and every good machine shop that serviced the racers had several pair of heads done and ready to go with the ARP rocker studs and proper seals. however that rule change was a few years back.

you dont need contacts. you need to pick up the phone. hell, go to any LKQ salvage across the US and get a pair of heads of pull-you-own un-known background heads from any 96-2000 half-ton with a R code vin for $75 each and take them to your local machine shop and have them freshened, converted to screw in rockers, change from the umbrella seals to good valve seals etc for about $250

or buy a brand new set of vortecs from GM for about $900. an extra $100 if you buy them with screw in rockers (I remember when they were $600 new)
 

sms986

Petty Officer 1st Class
Joined
Sep 18, 2017
Messages
239
The point of being in nascar country is that I am surrounded by car enthusiasts...

I'll call some shops today.
 

sms986

Petty Officer 1st Class
Joined
Sep 18, 2017
Messages
239
Called several shops. One had 906 casting heads. $300 stripped.

The guy did tell me that these heads are very, very prone to cracking. Questioning whether or not I want to put them on in place of pre-vortec heads.
 
Top