Pinging/Knocking

NewStangOwnr · May 2, 2008

I was driving on the onramp in 5th gear and all of a sudden the engine started pinging/knocking pretty bad. I went 5 more sec and shut the engine off and got it towed back to my house.

9:1 Compression. 91 Octane. I was running around 22deg total. 11deg BDC.

So closee on the break in. ****!

D.Hearne · May 3, 2008

22 degrees total isn't enough, it's retarded too much. 11*BTDC is OK, but still could be retarded. But from what you descibe, something else went wrong. New engine? Flat tappet cam? Could be it's wiped a lobe or two.

NewStangOwnr · May 3, 2008

I have a roller cam, I would be happy if it was that hahah.
I'm going to check the compression of those last two cylinders and report back.
How would I check for a wiped lobe?

D.Hearne · May 3, 2008

Well if it's a roller cam , a wiped lobe is a distant probability. If it did, there'd be a lot of damage from the lifter too. Lotsa noise as well. More than what could be called pinging.

NewStangOwnr · May 3, 2008

Very weird.

Well I checked all cylinders for compression and I couldn't get to one of them because of the headers, working on that. All came out to 165-175.

Very odd I say.

rbohm · May 3, 2008

check the mechanical advance mechanism for free operation, it sounds like it isnt working properly.

check your initial timing as it may have slipped.

if these check out, then likely you were in the wrong gear at the wrong speed for accelerating. you probably should have been in third gear and not fifth.

NewStangOwnr · May 3, 2008

Your talking about the weights and springs in the bottom of the dist. right?

NewStangOwnr · May 4, 2008

I was going to order a re-curve kit. Good idea?
Thanks for the help!
I have electronic ignition, Pertronix Xri if that helps any..

65ShelbyClone · May 4, 2008

Yeah, I think the problem is probably in your distributor. I don't think you need a recurve kit until you find out why yours is not advancing far enough.

You also shouldn't need to use 91 octane with just 9:1 compression. I have around 9.25:1 and mine doesn't ping with 87. I'm using a stock '85 GT distributor with 10° initial, ~38° total, and a low-overlap blower cam(keeps the dynamic compression higher). You should have more like 36° total timing by ~3500rpm, not 22°.

NewStangOwnr · May 4, 2008

Alright cool.

Well I tried to start it again today and was kinda scared, it seemed to backfire out the carb. Either way I'm going to check the distributor. I might just bring it to a shop around here and hopefully they can fix it, I just dont have that much time lately.
On the 91, I know, but it feels(felt... ) better on 91 than 89.

Thanks for the suggestions keep them coming

NewStangOwnr · May 5, 2008

Found I actually have the 15L weights in the dist. Gear was fine. so 38-40 is good timing right?

So weird.....arggghhhhhhhh

NewStangOwnr · May 6, 2008

I feel dumb and smart at the same time.
I forgot to check the other valve cover.
Guess what. This is the 2ND! stud that has snapped off.
The exhaust rocker arm broke off and was lying there.

D.Hearne · May 6, 2008

NewStangOwnr said:
I feel dumb and smart at the same time.
I forgot to check the other valve cover.
Guess what. This is the 2ND! stud that has snapped off.
The exhaust rocker arm broke off and was lying there.

Check the intake valve pushrod for that cylinder, it could be bent too. Intake in-------nothing out-------- equals a bent pushrod when the exhuast tries to escape back out the intake.

woodsnake · May 6, 2008

Did I miss the part where the pushrods were measured? For two rockers to break is not usual, at all...

NewStangOwnr · May 6, 2008

woodsnake said:
Did I miss the part where the pushrods were measured? For two rockers to break is not usual, at all...

Is it not?

rbohm · May 6, 2008

what are the cam specs in your motor, and what rocker arms are you running?

NewStangOwnr · May 6, 2008

http://store.summitracing.com/partdetail.asp?part=CCA-35-556-8&autoview=sku

1.6 RR
I ordered the pushrods a little short and they sit right about in the middle.

woodsnake · May 7, 2008

Can you be more specific about how you measured, the tools you used, etc...
Didn't I read somewhere that you had a shop build your short block?
I broke a rocker arm almost in half, I thought I punched a hole in the top of my piston it was so loud!

I'm thinking there is more going on here than meets the eye.....

NewStangOwnr · May 7, 2008

Yeah, a local builder put together the short block.
is the cam too big? I measured the pushrods with a pushrod checker? took off the guideplates and used 2 washers to recreate the thickness and measured..

D.Hearne · May 7, 2008

For a rocker to break, he also needs to check for spring bind.

Pinging/Knocking

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