Carbon on Piston Top/Dome

[ActionStarCBRxx]

Posting this for my nephew. He is at the wonderful age of 16... you remember more time than money and think you can do it all?!!

He has a 1989 Firebird with a 305 in it. The car is starting to go through quite a bit of oil and is losing power. He did a compression check and he thinks its the valve seals/guides. So his project is to pull the heads, compress the valves, clean everything up and replace the valve seals/guides. He has one head off and is still working on the other ( issue with damaged bolts that were stripped while trying to remove... T40's holding the bracket in place... wtf is chevy thinking)

Anyway's he is looking at the top of the pistons and they are really carboned up. He wants to scrap them and remove the carbon. I told him to wait that I thought it would be a bad idea. My thought was if he starts scraping and chipping that stuff away and doesn’t clean everything up perfect or if any particle falls/gets trapped between piston and cylinder wall that would be a bad thing.

So you know when you start a project it comes down to how much do you want to do to get it right... how much money do you have to make it right and how long can you be with out the means of transportation. He is a poor high school student that is covering his own car expenses so he doesn’t have much money.

Here are my two thoughts on the best way to handle this.

1) Let it be and don’t touch the pistons. If anything its adding to the compression ratio... but it could be keeping the flame from not getting a complete/good burn?

2) Pull the oil pan and undo the connecting rods and push the pistons up from underneath the engine block. This would allow a good sand blasting of the pistons and a chance to replace the rings.

Ideally there would be an option three 3) that reads pull the engine and disassemble and replace pistons/rings and take the block in and have it honed. But again I don’t think he can afford this.

I am open to suggestions and welcome the input. I admire him for his gumption of taking this on!!

[Northman]

If you're trying to keep this simple and cheap, soak the piston tops down with "Deep Creep", which is a Seafoam product. It softens & loosens carbon, while also acting as a lubricant. This will help remove the carbon from the piston tops, as well as the rings. Use a wood or plastic scraper & a lot of patience to clean off the carbon as that will help avoid scratching the pistons or bores, causing hot spots.

He might also want to get a machine shop to take a look at the heads when they're off. Replacing the seals may work temporarily but won't last long if the guides are worn.

[Fast Eddy]

He can run a clean up hone cheap. Since your there rings and bearing are not to expensive.

You don't often see this kind of thing working out well for the do it yourselfer.

You could call around salvage yards to see if there are any cheap used motors.

Good luck

[CxBXR]

Northman +1

An engine that age, with those symptoms is usually caused by a combination of things. (1) Carbon build up everywhere, pistons,head's,exhaust/intake ports. (2) worn out carburetor & worn out camshaft worn out valve springs, worn out piston rings OR worn out cylinder's.

You really cant do one without the other,

Piston ring's, hone, valve seals. (if it is burning oil either one of these could cause it)

Valve job can be done at home for less the $20

[cbrxxquad]

That carbon is a insulate, not nessasary to remove, unless heavy, could scrape off some.

We used to coat the tops of race pistons to cause some to build before coatings.

[R1000]

Just removing the carbon will not do any good. If it is a hard thin and dry carbon layer it is just sound. In case it is a thick and greasy layer the cause need to be fixed, e.g. worn piston/rings/bores and worn valve guides.

I get the impression that a used engine in good condition may be the best option. If the engine is quite worn and needs a renovation it is better to replace it. A quick and dirty fix like replacing valve seals is a waist of money. A good reason to make a complete renovation would be if the engine is unique, e.g. was the stock engine for a classic car, which is probably not the case with a small block Firebird -89.

[Furbird]

I'd clean the pistons off, do a valve job, and get the heads resurfaced while they're off to prevent any problems from arising. I would NOT pull the bottom end loose to replace just the rings. If you're going to pull the pistons out, you might as well rebuild the entire engine.

I can tell you this though. If the valve stem seals were leaking, that causes smoke on startup. Oil burnoff all the time is typically not valve stem seals. Since it's already apart and you want to get by for now, I'd do the above and button it back up. However, I would start saving up for a rebuild or another motor. It sounds to me like the rings are already causing blowby, so the valve job will help, but it's highly unlikely it's going to stop the oil consumption.

[Byrdman]

Junk it!

[CxBXR]

Junk it!

LS1 drop in ???

[ActionStarCBRxx]

Thanks all for the replies! I hadn’t considered just a flat out replacement from a junkyard... but that is a viable option in the near future if this doesn’t work out.

I like the idea of using the Deep Creep. And he will do that to the tops of the pistons.

I went over last night to see the progress and there is carbon build up everywhere on everything. The backs of the valves are thick and chunky nasty!! The top of the pistons have build up as well... not nearly as bad as the valves but they are big flakes. He is soaking the valves in kerosene and will use a wire wheel on a bench grinder to clean those up.

I bought him a angle die grinder and we were only able to find some stones and sand paper drums. We took one of the heads and did a clean up port on one of the chambers... mainly to smooth out radius and clean out the build up. I gave him a decent one to look at as an example. I emphasized over and over to stay away from where the valve seats and little is way better than too much when porting. We smoothed out the lip in the intake chamber where it turns down the runner passage and on the exhaust we just lightly cleaned/polished around the bowl. Re- emphasizing over and over to stay away from/becareful of where the stem the valve moves through the head. (Cant recall what that’s called) We smoothed the radius hump by where the spark plug sets as well. Again stressing not to worry about taking metal away but just smooth out the roughness and the bumps.

I suggested he not use the stones but use hardened steel bits. I gave him a few articles on porting so he can read and get the jest of what I was doing and why.

I might have gone a bit overboard on recommending the polishing... but when I was his age that was one of the things I remembered most about the rebuilds I did. (man twenty years ago!!) I screwed up a few heads and had to have the valve seats re-done because I scratched them with a bit!!

There is something to be said for experience in doing. Its funny that none of his friends are around helping him. This type of work is becoming a lost art it seems.

There is also something to be said for good engineering. Taking out some of those bolts was a real pain. And having to use T (8 star) sockets to pull an AC connected to a bracket seems real dumb. And using off sized bolts. 19/32 and 17/32 I think were two we had to use on some other brackets? You don’t see that kind of crap on a Honda.

[beondwacko]

Here's something that wasn't mentioned about the cylinder heads that I'm suprised about. If you sent the heads out to be cleaned and milled, if the shop mill's the head more than 0.010 , verify from the shop that the intake manifold being used won't have to be reangled as well. At 0.010 on an SBC, you won't have to worry about push rod issues. It's too little of a distance change.

I realize that this is a learning experience for the kid and it's great that he learns hands on. I'd also look into finding a set of used heads ( or and entire engine ) from a pull your own part kind of auto recycler. The Vortek 350's had GREAT factory cast iron heads. You can find them in vans and p/u trucks from 90'-99' ( and posssible other years as well ).

I always disliked 305's. Especially back in the day when the cams would go to shit or when they used a 58cc chambered cylinder head with 1.72"/1.50" valves. Those engines were almost as useless as 307's.