Thread: 305 Update: new gaskets, Dieseling, misc

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Hey guys, made a thread about cam on this 305 and what you guys thought. Well I DO NOT have solid lifters. Had my valve cover off because of a massive leak..


So I put on new gaskets.


So I had the first diesel a.k.a preignition in Months. It coincidently caused my valve cover leak to worsen? Anyways I read that I could be getting crappy gas so I'm going to not buy 87* grade and also not buy from 7/11! We will try 93* grade and a better station!

On my rockers I could see that it is like a "straw" (sorry for my terrible analogy) on my lifter so I therefore don't have solid lifters, so I also don't have a solid lifter cam, I have a hydrolic cam

Just an update of what I did today.

Also check the distributer base & oil pressure sending unit if there is still a leak.
What type gaskets did you get?

Felpro cork... It's all the parts houses had in stock.

I forgot to ask,

What do you guys think of "sea-foam"?

First let's talk about your gasoline. "Dieseling" of a gasoline engine is a totally different phenomena from "pre-ignition". Dieseling is the condition where the engine continues to "run" with the key off, meaning the engine is igniting the compressed air/fuel mixture without any spark. Carbon hot spots can lead to dieseling, and having too much throttle makes it worse. This is the reason one of the guys suggested that you might use that AC idle solenoid in a different way, having it energized to establish your normal idle; and the de-energizing it with key "OFF" to totally shut your throttle. Pre-ignition is a condition where the air/fuel mixture ignites slightly before the plug fires when driving under load, and is evidenced by "ping", "clatter" or in the worst cases "spark knock". If you're running too much advance, or if you're running gas too low in octane you get pre-ignition under load, going up a hill getting into the throttle, but not enough for the tranny to kick down is the classic example.

Now for octane. The higher the octane the slower the flame path moves across the piston, reducing cylinder pressures and minimizing "ping". In short, you want to run the lowest octane rating that you can without pre-ignition. You're throwing your money away by going to 93 octane fuel unless you have to have it. Higher octane fuel doesn't pack more power, and in fact it packs less per unit volume. You go to premium because you've packed the extra power mechanically - higher compression generally. If you find that you have to have premium fuel (which I seriously doubt in your 305) do yourself a favor and go to the HyVee at 119th & Ridgeview. They're the only station in your area that has premium fuel without ethanol added, and if you're going to pay for premium you might as well get all gasoline instead of decreasing your energy input with corn.

By "straws" I assume you're talking about the pushrods? With those OEM stamped steel rockers I doubt seriously that you have anything very "special" in the cam. Once we're clear on whether you're chasing a "dieseling" problem (run on with key off) or "pre-ignition" (ping & clatter at WOT under load) the path will be clearer.

I'm sorry, I've heard it called dieseling/pre-ignition. Had no IDE of a difference.

Great info,
Really helped my understanding. I'm at 119th and ridgeview about once a month.

Yeah I typed the wrong word, yes push rod. Not sure what I said? And you guys would be able to tell better than me? Hydrolic lifters aren't as aggressive as solid lifters so yeah its a mild cam for sure. Maybe an RV cam like a 268h I think is what someone said? I just posted that so there is no confusion on solid or hydrolic.

Timing is 8.5*BTDC so it's not too far advanced because stock would be 5* and vacume advance adds 2-3*.

So should I run 91* octane? I can't make it to hy-vee every 1 1/2 weeks.

Thanks so much, as you can see I'm a little clueless on certain matters!

Here's a close up (bad quality) of rockers/pushrods/head

I GOTTA agree on the petrol issue.

When I drove a big penske ( think u haul ) across the US last year, I fueled up with real petrol once, and the fuel economy increased ten percent, no $hit.

Of course, the moral of the story: if the US wants to reduce its oil imports by 10% tomorrow, all we need to do is stop using ethanol today.

Are you dealing with dieseling, or are you dealing with pre-ignition?

Assuming it's pre-ignition under load - If you can run 87 octane without pinging, then you get the most power from it. If you get a tiny bit of "ping" at heavy throttle under a load (driving up a hill, into the throttle, no kick down; or rolling start WOT) try backing out 1/2 degree of base timing and see if it goes away. If not then you may need to bump up to mid-grade 89 octane, but avoid that if you can. You get the most power by running the lowest octane you can run without ping, and a tiny bit of mild, random "clatter" at highway speed, WOT is telling you you're just about perfect on fuel choice, timing and mixture.

Get your gas from a good station that runs a lot of customers through every day so you know that their storage tanks are getting refreshed often. Around here QuikTrip is a good choice if you don't have to have no-ethanol gasoline, or any of the majors in a good, high traffic location.

As far as gas recommendations---for our customers that we are dealing with a tuning issue we STRONGLY insist that they have SHELL or BP---none of the off brands/convenient stores---


That carb tuning, dieseling,AND oil leak on the left side are all related to that ill fitting CHROME THINGIE on the left valve cover that is hooked to the carb base with braided hose---hugh vacume/oil laek and he has to be 2 1/2 turns out on idle mixture screws to give enough fuel--------


Also----on older GM ignitions---the inner shaft/advance mech seizes/rusts and won't advance/retard properly---causes mechs to chase timing problems as it sticks closed so they give it more advance , then it sticks advanced, get rattle/spark nock and then the mech retards it--then says carb must be bad, changes carb, etc, etc, etc,etc

Yeah Jerry, but your customers are dealing with engines that are built to the nines, pushing the envelope on compression & timing. This is a basically stock 305 with a mild RV style cam, so the selection of a fuel source is not nearly so critical. Much worse to go to a Shell station that gets ten customers per day than go to QuikTrip where they empty their tanks every three or four days, IMO.

Pretty sure he already addressed the turns out on the idle mixture, several posts back but I could be wrong.

A very good tip on the older GM distributor, and the tendency for the advance mechanism to get sticky and cause the shade tree mechanic to recommend all kinds of "fixes". Maybe a new distributor needs to be on the Christmas list.....

Little Chevy, tell us if you're chasing dieseling or pre-ignition, and while you're in there check the back of your intake really carefully with a mirror and light. That "china wall" gasket across the back of the intake to block is a common source for oil leaking on the SBC.

Rspears:

I didn't mention it but I have a brand new HEI distributer. I bought it last December when I ha to replace my intake manifold gasket because my plugs keeped fouling. Carb is 6 mo. Old and dizzy is 1 year old. It would probably have helped, I had to replace gaskets and dizzy.


This is how I could run the block.

Now had to assemble it back together with new gaskets.




So we had some suspicion when the timing cover has red RTV.

So has it been dieseling, or have you had pre-ignition under heavy load/WOT? Third or fourth time for this question....

My apologies: Dieseling, engine (only once in 4 or so months) just tried to keep running. "Clunk..clunk,clunk...clunk... Pop" carb backfired.

Sorry, I just noticed that your thread title says "Dieseling", so I should have known. Is your carb one of the newer "Thunder" series that eliminated the power valve? If not, you need to check it because any little back fire can rupture the power valve diaphragm, and you say you had a big "Pop". It's worth checking to know it's OK.

No not a loud pop at all, it backfired but a small one.

How can I check the power valve?