Flywheel knocking...?

[eutechnyx]

I have an oldschool 350 sbc in my 87 s10 blazer and when i start it up I get a knocking noise for about 1 second and its gone it used to do it after i drive it and start it back up but now ive noticed it just about everytime i start it,the motor is fine though,i can rev it all day long and the motor sounds strong as hell so im sure its nothing major,I was going to replace the timing chain and adjuster and see if that fixes it but now im seeing where people are saying it could be flywheel bolts are loose or something like that or even exhaust but i doubt its the exhaust,I figured id post it here and see what you guys think and if you have any suggestions on determining what it is.oh btw the motor only has about 5,000 miles on it or so and the sound is alot like the sound it makes when you dont drive it for a few days and change the oil,that initial sound it makes on start alright thanks guys!!

[lowxpectationz20]

i had my torqe converter bolts do that on mine, shortly after I put it together. I would shut it off and it would make a knocking noise, and when I would fire it up it would do the same thing.

[eutechnyx]

Do i have to pull the tranny out to check them or can i adjust them without doing that? I have a TH350 tranny I can see the flywheel when im laying down under the truck there is no guard or anything

[joelkatdaddy]

Also check for a boken flexplate. IF you sinched the torque converter down to the flexplate at an odd angle it WILL crack and it will sound just like a knock. Pull the torque converter inspection cover off and get a small mirror and give it a look.
Joel

[lowxpectationz20]

joel is 100% correct. You also can tighten up the torque converter bolts without removing the trans, If you look up between your torque converter and your flexplate, you will be able to see three bolts, in a triangle pattern holding your converter to the plate. You can stick a wrench right in there and tighten them up.

[SH-60B]

Try running a straight 30 weight oil on the next oil change. What is the oil pressure?

[eutechnyx]

I'm running 20 50 in it now the oil pressure is and has always been a bit low once warmed up but like i said its an oldschool motor early 70's it gets about 10 psi at 700 rpm idle and 25 psi at 2 grand but the normal is 10 psi for every 1000 rpm to be safe my dad is an oldschooler and said that it is pretty much normal is straight 30 thicker than 20 50?

[SH-60B]

The oil pressure is fine. 30 to 20-50? IDK if it's thicker or not, but oil pressure is good so it doesn't really matter.

[5timedime]

i had a cracked flexplate on the 305 in my 85 camaro and it made a nice little knock like that. since there's no gravel guard on it, you can easily inspect it with a flashlight and a mirror. and definitely check the torque converter bolts for tightness. those two are good places to start and are also easy on your situation.

[eutechnyx]

ok thanks alot guys i appreciate the help ill check it out friday when im off,Im guessing its gotta be one of those ill let you guys know thanks again!!

[eutechnyx]

Ok I went under there and examined it and it looked fine I could only get to one of the bolts though the other ones were really high up there but the one i could get to was nice and tight and i couldnt get to the converter bolts I took a vid and stuff but it didnt show much helpful so i didnt post it,it could still be the bolts are loose up there any suggestions on reaching the converter bolts that hold it to the flexplate up top?

[joelkatdaddy]

Turn the motor over. Either get a flywheel wrench, or a socket with a breaker bar on the balancer bolt, or mark the bolt with a sharpee and crank the motor over and look again. WHen you see 1 of the 3 bolts facing down with no sharpee mark...check how tight it is.
Joel

[LXtasy]

Have you made sure your starter was aligned right? If mine gets off just a HAIR it does the very same thing.

[eutechnyx]

I'm not too sure how to check starter alignment how would i go about doing that? My mechanic can prob do that for me

[LXtasy]

Loosen it up and push it all the way towards the passenger side framerail. Than tighten up and try it again.Do you have mini starter or the big ole boy

[eutechnyx]

Ive got the big ole starter

[joelkatdaddy]

If you are using proper stater bolts that wont happen. Starter bolts have a knurled shaft on them. Im betting your flexplate is cracked. They can be tricky to spot.