Motor Problem- Rings and/ or Valve

[F14JetJock]

Hi,
I'm looking for some help or advice with an engine problem. I've called several engine shops in the Ventura CA area. One told me that they don't work on "old" motors (although they might have someone that might work on old motors on his own time) and another told me that they might be able to squeeze me in at the end of 2005 (I thought I heard him wrong and he reiterated it would be over a year before he could get to me) !
I have a 350ci / 350 hp motor cast in 1973, running in my '69. In a forum from last year ... http://corvetteactioncenter.com/forums/showthread.php?t=33451&highlight=valve+cover+blow

SteveL had a similar problem....
I have the same blow by out of the valve cover that he had, the dreaded "puff of death". no water in the oil, no smoke out the pipes. I did a compression check and found one dead cylinder (#3 is 60 psi dry / 65 wet). The other cylinders are all 148 to 156 psi. I haven't done a leak down test because, with a "dead hole", I thought that it would just confirm a bad/burned valve. Mako, in the referenced forum, indicated that he "likes to see north of 150 pounds on a stock engine, and say 180+ on a performance engine". With these compression targets in mind, I suppose I have some leaky rings as well as a bad valve???

Here is the question. How would I trouble shoot these problems, in a logical manner ?

Should I take it to the machine shop to have just the #3 valve fixed (I've checked to see if it was something simple like a broken spring / rocker). I know that most would say, if you get one valve done, get them all done. A valve job might not be the entire cause of the problem. Could a bad valve (60 psi) be the cause of the blow by?

If fixing the valve on #3 cures the blow by and then doing a leak down test checks out OK, I will be able to get a bit more life out of the power plant. If not, then it looks like a complete engine overhaul for the rings, etc. I think I would rather put a crate motor in, since it is not a # matching motor anyway, than do a complete overhaul.
Your sage advice would be greatly appreciated......

 

[Vettehead Mikey]

Bad valves don't cause blow by.

You have low compression on a cylinder AND heavy blow by. I bet a case of alumibeer that's it's bad rings/scored cylinder wall on #3.

 

[Bob Chadwick]

That would have to be a really bad ring/score for a "wet" check to only increase compression by 5 pounds. Leak down test on just the one piston would probably tell you for sure what the problem is.

 

[gravismaximus]

maybe a broken ring, a bent or craked valve, and i dont see if you had hevy carbon deposits maybe from a misfire cylider you didnt know about could cause blow by. no matter what thou to get the valve out you gota take the head off, so just do them all. and rebluid the lower end. you now its worth it to get extra hp

 

[MMM]

A word of caution, if the engine is high mileage (> 100,000) and if it is a burnt valve, doing a valve job alone is iffy. The valve and ring seals create the compression seal in the cylinders. As the engine is operated both wear evenly. If in a high mileage engine, one of the two is renewed (usually the valves because it is easier to do) then the other suffers. In plain english, if you do a valve job only to a high mileage engine, you immediately start to burn a lot of oil (at least 80% of the time). If you got blowby now, just wait.
Having been a motorhead all my life, I have been asked by many, "I just had a valve job done to my car and now it uses oil, what gives?" I tell them the bad news, they now need to replace the rings too and depending on the bore wear, that gets expensive. If faced with a burnt valve situation on a high mileage engine, unless it was ok to do a total rebuild, I always replaced and reseated only the bad valve.
Mike

 

[vette-dude]

I think I would opt for a crate motor and replace the whole thing. Of course maybe you are trying to keep it original and matching numbers. Then you will have to do it the old fashion way. Sound to me like you need to overhaul the whole engine.

Randy

PS Sorry missed the part about it not being a matching motor car. Try Jasper Engines for a motor and installation or Summit Racing for a crate motor and find someone to install it (unless you can do it yourself).

 

[GerryLP]

If you want the Vette to be back in business as soon as possible, then I suggest replacing it with a crate motor. The key factor, of course, is funds available, but if it is not a factor, then slap a new crate motor in her. Later, and you can tinker at your own pace with the old and tired motor, and determine if it's worth repairing. Crate motors are by far a cheaper option than repairing in the long haul.

Just in time for the hollydays!!!!!!

GerryLP:cool

 

[F14JetJock]

Thanks for all the timely replies !

I agree with the argument that a crate motor is the way to go. I also have a understanding wife that wants to go in that direction. (Go figure. A wife that wants you to spend money on the "mistress" !!)

My friends (one has a '65 Vette and the other has a '67) suggested that I get a complete valve job. Mike, your comment has helped me make up my mind. Thanks!! This motor has over 100K miles on it and throwing good money after bad is not what I had in mind. I'll take it in to have only the bad valve replaced and seated .... and start looking / drooling over the new crate motor that is going into "she who must be obeyed".

Thanks all and HAPPY HOLIDAYS !!

 

[Jack]

Given you have NOM & the symptoms and the time & labor involved with head R&R, replace seat machinework etc ... I like crate motor option. GM-Goodwrench offers a crate motor very similar to L48 and has 250 HP ... everything from valve covers to pan 100% brand new with 36 month/50K mile GM-Goodwrench warranty for $1200 - $1400 depending where you buy. Please note: many new crate motors have "one-piece" rear main seal crankshafts ... 1-piece has different bolt pattern on end of crank that will not fit your 2-piece seal flywheel/flexplate. You would have to get a new flywheel/flexplate if you go with a one-piece seal motor. Everything else on/from your 69/73 motor will bolt up. You could R&R cam in new motor with a $75 L82 cam and expect about 275 HP. If you&your friends can R&R motor you could be back in saddle w/ NEW motor w/good warranty for about $1500.

BTW ... worn timing chain/pumped up lifter/weak valve spring can cause piston to hit valve and bend valve. New valve relatively cheap ... Replace seat is $costly. G'Luck.
JACK:gap

-edit- seems you're near Ventura. I think ARP bolt company is around there or Camarillo/Oxnard ... drop by there ... likely someone there will know exactly where to go for "older" motor repairs & more. No doubt there's a gearhead or 2 working at ARP.

 

[wishuwerehere82]

Man, I can't believe with all the hot rods and low riders around So. Cal you can't find a speed shop that works on SB Chevy's.

 

[F14JetJock]

Thanks Jack. I appreciate your thoughtful advice.

 

[Hib Halverson]

Hi,
(snip)
I have the same blow by out of the valve cover that he had, the dreaded "puff of death". no water in the oil, no smoke out the pipes. I did a compression check and found one dead cylinder (#3 is 60 psi dry / 65 wet). The other cylinders are all 148 to 156 psi. I haven't done a leak down test because, with a "dead hole", I thought that it would just confirm a bad/burned valve. Mako, in the referenced forum, indicated that he "likes to see north of 150 pounds on a stock engine, and say 180+ on a performance engine". With these compression targets in mind, I suppose I have some leaky rings as well as a bad valve???

(snip)

If I read the above correctly, you have both low compression in one cylinder and "puffing" out the PCV connection on the valve cover during cranking.

I'd say you have either a broken ring or a fractured or burned piston in that hole.

You either need to overhaul the engine or, as others have suggested, stick a crate motor in there.

I would ignore the advice "150 lbs on a stock engine and 180+ on a performance engine" as it is not correct. If the engine is stock, use the compression specifications in the service manual for your model year. On modified engines, compression will vary depending on static compression ratio and camshaft profile. For example, a 13:1 drag racing engine with a very radical cam, might have fairly low compression pressure at cranking speeds and a 9.75:1 street engine with a short duration hyd. roller, may have fairly high compression pressure at cranking speeds.

 

[AKRAY4PLAY]

a new engine is good. but there might be something simple that is wrong. i have seen several old motors that have somehow aligned the ring gaps. this caused serious blowby and all the symtoms you describe. i would do the leak down on the #3 hole, it will tell where your compression is going and help zero in on the problem. find the problem and then decide what is the best option to fix it. it is a good probabilty that your piston and/or rings in that hole are gone, but you won't know unless you do a leak-down or disassemble the motor. Brian

 

[F14JetJock]

Brian,
I agree. Rather than proactively dropping a new motor in the car (chances are that it will have to be done anyway), I think a leak down test on #3 is at least the minimum that should be done. I'll better know what I'm dealing with.
Happy Holidays
Bill

Hib, Wouldn't a leak down test tell you if you had bad rings etc?

 

[Hib Halverson]

If a compression test shows 60 in one hole, a leakage test ain't going to tell you any more than you have a hell of a big leakage.

You have your symptoms
1) very low compression in one cylinder
2) pulsing or "puffing" out the PCV.
3) 100,000+ miles on the engine.

I think you need an overhaul. If the leakage test leads to any other useful solution, I'll buy the beer.

 

[AKRAY4PLAY]

Hib,
not meaning to be arguementative, but my view is a little different. since it is a high milage motor, the puffing on the PCV could be coming from all the cylinders combined. the leak down test is just to verify the path of the pressure loss. as stated earlier in the post, the possibility of a slighly tweaked valve or blown valve seat could explain the low cylinder. it would give the proof of what is wrong and better aid in making the right decision of fixing or replacing the motor. granted, the vast majority of replies agree the lower end of the motor is the problem, but without the leak-down test it is just a well educated guess.
Brian

 

[F14JetJock]

Hib,
I'm sure your right about the motor needing an overhaul (I'd be happy to buy the beer, by the way !). I was just trying to determine the methodology to come to that conclusion. You pretty much summed it up, in your reply.
As a former Navy test pilot, I know fighter jets and jet systems.... It is the Terra Firma based craft that I'm trying to learn more about (in my second childhood). I'm not a mechanic by any stretch of the imagination.... but I'm learning.
Thanks for your insight.
Bill

 

[F14JetJock]

Hib,
not meaning to be arguementative, but my view is a little different. since it is a high milage motor, the puffing on the PCV could be coming from all the cylinders combined. the leak down test is just to verify the path of the pressure loss. as stated earlier in the post, the possibility of a slighly tweaked valve or blown valve seat could explain the low cylinder. it would give the proof of what is wrong and better aid in making the right decision of fixing or replacing the motor. granted, the vast majority of replies agree the lower end of the motor is the problem, but without the leak-down test it is just a well educated guess.
Brian

Brian,
If, for arguments sake, you had a bad valve and/or blown valve seat, how do you do a leak down test? I assume you would have to seat the valve or plug the hole somehow to pressure check the rings/cylinder. With out doing this first, wouldn't pressure leak past the valve? If so, how do I plug/seat the valve? I think that, at the very least, this would be a good learning experience and, even if the motor needs to be replaced, this procedure won't throw a bucket full of $ at the wrong solution to the problem.
Regards,
Bill

 

[AKRAY4PLAY]

Bill,
the leak-down test i use is a crude one just for troubleshooting. i would put the #3 hole on the compression stroke, easily verified by popping the distributor cap and seeing the rotor pointed at the #3 terminal. set it so it is before the the terminal, about 3/4's the way from the #4 terminal to the #3 terminal. this should put the valves in the closed position, also verifying the valves with the valve cover off helps. remove the spark plug and blow air from a compressor into the plug hole. a rubber tipped air nossel should seal in the plug hole and pressurize the cylinder. find where the air is escaping and that will determine the problem area to look at. air out the intake - intake valve, exhaust - exhaust valve, PCV - rings and/or piston. if the problem is from the piston or rings, you can pour some STP oil treatment into the cylinder through the plug hole. the STP is thick enough to seal the rings and another application of air should give you a better idea of a cracked piston or bad rings. in any case, the test should not cost you any money and still give a better idea of what is happening inside the motor.

you may also want to talk with your flight mechanics in the turbine test bay on base. they have some real nifty bore sights that could go into the spark plug hole and look around in the cylinder. kind of fun to probe around in there, and it should'nt cost anything either besides time. enjoy wrenching! i always feel a ton better knowing exactly what is going on especially when several thousand dollars are hanging in the balance. good luck figuring it out and post more questions if you have them, we'll do what we can to help you out.
Brian

 

[F14JetJock]

Brian,
Thanks for the info. Makes a lot of sense and doesn't cost anything. Looks like I have a project for this weekend.