Valve stem seals info needed and is it worth while in my case?

[SirRobyn0]

Ok so the engine in question is the 305 in my 84 C20. Mileage on the engine is unknown. Over all health of the engine is good and it's been taken care of and isn't slugged up. Compression is good and even, runs good oil pressure even when warmed up on hot days. I've got another thread or two on my spark plug fouling woes, but basically the summary is #7 suddenly oil fouled, truck has had a long history of giving a puff of blue at start up. Now I can only go a few hundred miles before I'll foul out #7, but over all oil use is nill so I feel it's all or mostly going into #7. I never see smoke while going down the road, but the truck has a cat in good health so that could possibly be masking it.

Symptoms, fouls out #7 when it starts to foul misfire will be noticed at idle, and progress to full misfire. Now another thing, if I run the engine hard like lets say I'm loaded or towing my trailer, I'm likely to go up a hill floored or near floored at relatively high RPM maybe 3K - close to 4K, you know in the power band. It's likely to mis after that, is it possible or likely for SBC to pull oil though the valve stem seal under those conditions. We have discussed at work that might be any of the valves not sealing when it gets a little extra hot, a weak spring or seat, but I have no other symptoms of that kind of issue, no backfiring or popping.

So I'm about ready to pull the trigger on a reman 350, but I hardly have the time for the install and money is always tight. I briefly thought about tossing remanded heads on the 305, but if there is any chance of lower end issues I don't wanna put the time and money into that but, I might be willing to put valve stem seals on at least #7 and see what happens.

As you guys know I'm a long time mechanic, but not an engine builder at all. So I'd like thoughts / opinions.
#1. Misfire after a long hill at high RPM and throttle, any chance this is oil sucked past valve stem seal?
#2. Replace factory o-ring type seals, use umbrella seals, or both?
#3. Do just #7, all of them on that head or both heads?
#4. Is it worth while to replace the springs on how ever many seals I do?
#5. Is it even worth while to do valve stem seals? or is it time to stop screwing around and put a 350 in it?

Open to other ideas and thoughts, but not interested in LS swap. Thanks.

 

[Snoots]

On the cheep $$$, I'd do #2 on #7.

 

[Bextreme04]

I had 305 heads on my 350. One of the valve springs broke, so I needed to replace at least that one. I just bought a set of comp cams stock replacement springs for $50 and a set of umbrella seals. I used a compression tester hose with the valve removed to hold the valves up and then replaced the springs and added umbrella seals on all of the valves with everything still in place. It was a pain in the butt, but it worked well. I would recommend just adding an umbrella seal on both valves for #7 and see what it does. It did help with my plugs looking all carboned up.

I would bet your misfire after a long pull is actually preignition from carbon buildup on the chamber surface and piston head after it gets super hot in there. The carbon buildup is always there, but its more susceptible to the pre-ignition after the engine has been running at high cylinder pressures for extended periods of time under a heavy load. Lots of heat soak into all those materials and the hot carbon will act like a candle wick.

 

[Grit dog]

IMO, considering your time is worth something, but valve stem seals are super cheap and you're a mechanic, I'd take 1 stab at new seals on #7 and see what happens.
Worst case you waste an hour or 2 and have 14 spare valve stem seals?
Doesn't feel like a case of throwing the baby out with the bathwater unless you're wanting a 350 more than you're wanting to write the check for it, lol. (If you use a credit card, that's like 4000 airline miles though! lol)
Seems to be your only real issue with the engine, correct?

 

[Grit dog]

I had 305 heads on my 350. One of the valve springs broke, so I needed to replace at least that one. I just bought a set of comp cams stock replacement springs for $50 and a set of umbrella seals. I used a compression tester hose with the valve removed to hold the valves up and then replaced the springs and added umbrella seals on all of the valves with everything still in place. It was a pain in the butt, but it worked well. I would recommend just adding an umbrella seal on both valves for #7 and see what it does. It did help with my plugs looking all carboned up.

I would bet your misfire after a long pull is actually preignition from carbon buildup on the chamber surface and piston head after it gets super hot in there. The carbon buildup is always there, but its more susceptible to the pre-ignition after the engine has been running at high cylinder pressures for extended periods of time under a heavy load. Lots of heat soak into all those materials and the hot carbon will act like a candle wick.

Serious question, wouldn't pre-ignition sound like pinging, not a misfire?

 

[WP29P4A]

Since the valve seals come in a set, and you have to take the valve cover off to change #7, why not replace all the seals on that side while you have the parts and you have access? In my business when the first one starts to go we don't just replace that one and then wait a few months and do it again, preforming the same labor again and again. When the first one goes bad we replace all of them so we don't have to do the same labor again for 7 to 10 years. In my business it's real simple math, it costs far less (in labor) to replace all of them at the same time, instead of chasing the problem. Just my opinion.

 

[scrap--metal]

I did umbrella valve seals on a 305 about 12 years ago. It was a used Target Master engine I put in my Monte Carlo to replace the very tired original 305. Since the engine was new to my vehicle, I can't say how much of a difference it made but it didn't hurt. The set of umbrella seals I got was missing one, so Summit or Jegs sent me another full set so I could finish the job.

Let me know if you decide to only do a couple of the seals, and I will see if I still have them around the garage. I could throw them in an envelope and mail them to you if you're interested.

 

[fast 99]

Back in the day, replacing the seals was done quite often. It isn't hard just time consuming. Depending on the option package 3-4 hours labor. The results were almost always worthwhile.

 

[Bextreme04]

Since the valve seals come in a set, and you have to take the valve cover off to change #7, why not replace all the seals on that side while you have the parts and you have access? In my business when the first one starts to go we don't just replace that one and then wait a few months and do it again, preforming the same labor again and again. When the first one goes bad we replace all of them so we don't have to do the same labor again for 7 to 10 years. In my business it's real simple math, it costs far less (in labor) to replace all of them at the same time, instead of chasing the problem. Just my opinion.

Because he isn't redoing them... he doesn't have any on it now. Most of these older SBC have just an oring seal on them or even nothing at all on them. Its a difference of 20 minutes compared to maybe hours of effort, plus the possibility of breaking something or dropping a valve goes up with every one you do.

 

[SirRobyn0]

Oh, wow everybody thanks for the feedback so far I really appreciate it. @Bextreme04 I was going to mention that I can get a full set of stock springs for $45 IDK the brand name off hand I looked it up yesterday at work. About $30 for a full set of umbrella seals. So for $75 I'll have enough to do all 16 seals and springs. I'm kind of thinking for the small cost I may as well do the springs on however many cylinders I decide to do, or is there some reason that might not be the best idea? As for the after hill misfire I did do a pretty serious decarb before the last tune up, but that isn't a guaranty of no carbon. I had not thought of that. I guess in the end it'll come down to doing the seals and seeing what happens.

But @WP29P4A I understand what you are saying about doing all the cylinders on that bank at least. If I was doing a brake job I'd do the pads on both sides of course. And honestly I'm a little torn on doing just #7 or the entire bank, but in the end what it might come down to is how much time I have once I'm in there and how I feel after I'm though with #7. I think for this job I'm more inclined to prescribe to the "the possibility of breaking something or dropping a valve goes up with every one you do" and keep in mind I'm a mechanic but never taken a valve spring off and held a valve up with the cylinder head on, so I'm a novice at that. Plus if I need to do others in the future, how long does it really take to remove a SBC valve cover anyway about 10 minutes, they come off pretty quick. I kind of doubt this engine will still be going in 7 - 10 years. My primary goal is to buy time at this point. Ok, I think that helps make the decision clearer for me.

@scrap--metal I appreciate the offer and while I probably would not need a full set, I'd probably be more inclined to purchase the set so I'd have the others on hand if needed.

 

[SirRobyn0]

IMO, considering your time is worth something, but valve stem seals are super cheap and you're a mechanic, I'd take 1 stab at new seals on #7 and see what happens.
Worst case you waste an hour or 2 and have 14 spare valve stem seals?
Doesn't feel like a case of throwing the baby out with the bathwater unless you're wanting a 350 more than you're wanting to write the check for it, lol. (If you use a credit card, that's like 4000 airline miles though! lol)
Seems to be your only real issue with the engine, correct?

Basically yes, all my other issues are peripherals. My EGR passage in the intake is mostly clogged, and my knock sensor needs to be relocated to the other side of the block so my ESC functions correctly. I've put off fixing that stuff on hold until I know I won't be ripping it out right away for a 350. Sure of course, I'd like the benefits of a 350 over the 305, but I'm fine with the 305 as well, it's done everything I've asked it to do after all.

 

[SirRobyn0]

Maybe I should consider doing the #7 stem seals and intake manifold at the same time. I'll think on that.

 

[75gmck25]

I would fix the valve seals, and then really think hard before going down the crate engine route.

The cheapest new crate engines (like the GM 350/240 hp) are old-school, low compression, flat tappet engines with really poor flowing cylinder heads. They work, but are a very poor base for future performance improvements. And they still cost $2k and up. The better crate engines are more in the $3.5k and up range.

If you could find a junkyard factory roller-cam 350 with Vortec heads at a reasonable price that would be a good swap. However, even then you have to worry about possible issues with Vortec head cracks.

 

[SirRobyn0]

I would fix the valve seals, and then really think hard before going down the crate engine route.

The cheapest new crate engines (like the GM 350/240 hp) are old-school, low compression, flat tappet engines with really poor flowing cylinder heads. They work, but are a very poor base for future performance improvements. And they still cost $2k and up. The better crate engines are more in the $3.5k and up range.

If you could find a junkyard factory roller-cam 350 with Vortec heads at a reasonable price that would be a good swap. However, even then you have to worry about possible issues with Vortec head cracks.

I know what you mean about crate engines. There is a place in Spokane that I can get a wholesale discount on a stock crate engine for about $1,500 and I trust their work, but I'm still a tight *** while I really don't have a problem with going to a 350 if I can safe the 305 with a reasonable amount of work I'd rather go that route.

I've thought about the vortec thing and there are certainly benefits for sure. Mainly if I got a crate vortec is would be about the same price as the old school 350. I'd be a lot more comfortable used vortec as well since they were made more recently, but the downsides.... IDK, some people seem to have runabilty issues with carbed vortec's and I'd most certainly have to go to a electric fuel pump. I don't think I'm really interesting in a vortec and I'm definitely not interested in a LS.

I'm running an age old, but in good health 700R4, which I have no idea if or when it was rebuilt, so for that reason I assume it's stock inside and I need to be careful how much power I put into it or I'll be doing a tranny too.

 

[Goldie Driver]

My buddy and I did valve stem seals on the 91 Sub we had ( me 1st, then it was his).
Used my air compressor, a spark plug chuck I guess he got/had, and rented a tool from Vato Zone. The 91 was easy to get the valve covers off for the most part and we did all 16. Kind of a time consuming job. I think I would experiment with # 7 only just so you are seeing only the results of one change at a time, but have the parts do to the other 3 on that bank down the road.