Replacing valve stem seals in 305 HO small block chevy from 1986 Monte Carlo SS

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I’m putting the original 305HO back in the Monte after taking the ZZ3 out for my Iroc project. This is mainly to make the car mobile but it may end up tagged with this engine for a while. Previous owner reported that this 305 has over 100k miles on it and has been out of the car since 1997. He said it smoked during startup and sure enough the valve stem seals were worn out. Hopefully this will fix the issue.


Homerhey says:

Also need to put some oil on the valve before installing the Viton or rubber depending, umbrella seal as well as the o-ring seal.. They also make a cheaper tool for this that u pull and release(rocker nuts used to pivot from) All chevy engines with centerbolt valve covers were designed with more clearance on the exhaust valveguide seal which means it leaks sooner. Smoke when you 1st start it and quits or while idling. This will fix that 90% of the time.

Homerhey says:

Using an air gun to remove the rocker arm nuts killin those off but they really need to be changed anyhow so in 1000 miles you dont develop any ticking causing you to remove the valve covers and re-adjust the valve lash. When using that hammer to release the stuck valve locks Dont hit the valve head as that can mushroom and cause more trouble later.Dont waste time trying to pick that dead o-ring seal out before pulling the spring off.It comes off usually as u release the pressure on the spring.

streetlegl says:

I wouldnt let this moron clean my windows cause he just find an easier way to do it. you dumbass.

zz3astro says:

It’s a good idea to go to TDC for the reason you mentioned. In this case, the engine was out of the car so it would have been easy enough to deal with a dropped valve.. That said, I’ve never heard of one dropping using this method.

BIOYA50 says:

Simple and easy for any backyard mechanic to understand. Video well done.
I did notice one thing is that you never mentioned whether you rotate the crank to bring piston in each cylinder up to TDC (Top Dead Center- or end of travel of the piston upward motion) before changing out seals, or was the engine tight enough in each cylinder that the rings held the piston in place? I always preferred to bring to TDC in case something slipped and the piston stopped valve from dropping into cylinder. ??

64fairlane305 says:

I`m doing this w.o. the compressor, pistons on top and choke the valves into the pistons as carefully as possible to make the locks slip

Nina Peratrovich says:

toatlly did it wrong your supposed to hit it with a hammer till it stops running lol

sheldonv8 says:

Nice video chap……Ive got to do the seals on my ’91 Caprice NYPD car..Need to get me one of those spring compressors!!!

skulledmonte84 says:

Got this video bookmarked lol thanks

zz3astro says:

Yep.. this is always the fix for startup-only smoke on small block chevy’s.

zz3astro says:

My compressor will only do about 100. Not really sure if I bothered to crank up the regulator so could have been anything from 80 to 105 psi. Figure on a 1.60 echaust valve you have 2 square inches of surface area so the up-force on the valve stem is 2 x psi.

doug eckard says:

how much psi on the cylinder

zz3astro says:

Some people like to keep them in order. It has never been a problem for me with either flat tappet or roller lifter engines. I put over 50k miles on my V8 Astro after mixing the pushrods up. In the case of this engine, it is flat tappet so the lifters spin anyway. 

zz3astro says:

It’s a Proform.. Not sure of the model number – I borrowed it from a friend. Just google for Porform valve sping compressor and you’ll see it.

deejaedub says:

Where did you get that valve spring compressor? I want one!

moparmania74 says:

are you serious? you really think its a good idea to switch the pushrods around? wow. good luck with that buddy… im sure that engine will run trouble free for hundreds of miles….

zz3astro says:

Thanks.. how I’ve always done the rockers is to spin the pushrod with one hand while tightening the rocker nut with the other. As soon as I feel the pushrod start grabbing (from the rocker arm beginning to push on it), I turn the nut 1/2 to 3/4 tighter and stop. Of course I make sure the cam is not trying to open the valve I am adjusting. Easiest way to do that is make sure the opposing valve is opening.

SuperSportSS says:

Awesome video. Im going to use this video to help me change my seals on my 85 IROC-Z but I was wondering how you go about adjusting the rockers? Thanks.

pntba11er16 says:

Great vid, and nice Iroc!

TwistedBinderz says:

Thanks for the vid very nice

Dave Mashburn says:

where did you get that spring tool at??

cheguevara778 says:

I dont know why I wrote cacle it should be valve …Damn iPhone!!!!

cheguevara778 says:

Im trying to replace all my calce seals on my chevy 81 longbed it has a 350 it looks the same as this hope it helps me…..Thanks for the great vid

zz3astro says:

Thank you…  I think it took a little under two hours to complete.. of course that’s on an engine stand so it’s easier to move the air fitting to each cylinder!

Ricky Risnandar says:

how much time did you use by the way?

Ricky Risnandar says:

nice vid, sir…

zz3astro says:

You’re off by one year.. they made the changes in 88, including making 15″ wheels standard and 16″ optional, along with the difference in the appearance of the 16″ wheels. I prefer the look of the earlier verison like we have.

U2wild says:

Coulda swore the Iroc was an ’85 or ’86 because of the placement of the iroc decal on the door. The 85 and ’86 were closer toward the front fender, in 1987 they changed the placement toward the rear about a foot and a half backwards =Yours is like the 85 and 86’s

zz3astro says:

Thanks… Iroc is an 87!

U2wild says:

Great info video- that’s funny I have Black Iroc-z just like yours in my garage LOL- Mine is a 1986- is yours???

Rohan Huie says:

Thanks for the tool number I found it on

zz3astro says:

Well it was borrowed so I can’t be sure of the exact model, but I’m pretty sure it is Proform part number 66784. It’s around $45 and the best spring compressor I’ve used for this kind of job!

zz3astro says:

At 3:20 I install an air line fitting into the spark plug hole. This uses air from the air compressor to keep the valves in place. Works well!

Rohan Huie says:

Love the video love the tool, do you have a number for that tool I need one if I cant get it I will have to make one, my question is on the umbrella seals, how does the plastic ones ( exhaust) work? because the don’t seems to stay down on the stem base and they fits so tight on the valve stem that they goes up and stay up not like the intake seals that has a band that keeps it tight to the stem base.
Thanks keep up the good work.

zz3astro says:

The one that was kinda hanging off? Valve cover gaskets. If you have it done at a shop they will replace those anyway. Ballpark cost for a shop to do a pushrod V8 like this 305 is $350-$400. Good luck on yours!

mrrudedaddy says:

wow thamks alot for the info,i thought it was the head gasket but now im sure this is the problem with my ram,it has alot of milage….is this an expesive fix at a mechanic?i dont know if i want to attemt this myself…also that first gasket you removed what is that? i think mine is done! seems to be oil leaking from that spot.

keasy84 says:

that’s cool to see it’s so clean after so long and so many miles. Apparently the bottom end and cam/lifters are in good shape too. It must have been well taken care of before.

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