Camshaft replacement

[mdsbch]

Well I took my 85 coupe (automatic) in to the shop because it was getting some detonation when under load and above 3000 rpm. Here is what they told me. The number two cam lobe is shot. This is causing the exhaust valve not to open far enough or long enough to allow the exhaust gasses to escape completely. Then when the intake valve opens the remaining exhaust gasses escape back into the intake (you can hear a little backfiring) causing the next round to be leaner and therefore detonating. The detonation only happens under a load, but you can hear a faint backfiring when revved up in park. They quoted me $4300 for an engine rebuild (which they recomend) and $2700 to replace the cam shaft. Since I have two kids in college right now, it is going to have to either wait or I will have to do it myself.

Here are some questions I have. If anyone can help with advice, I would greatly appreciate it. Thanks.

(1) - Is this something that will be Ok if I baby it for a while (keeping it under 3000 rpm)?

To replace the cam myself.
(2) - What is the stock cam for the 85 350 TPI engine?
(3) - Does anyone have any tips or things to beware of when replacing a cam?
(4) - The service manual basically tells you to remove everything from the front of the engine as well as the radiator. Does the transmission fluid cooler in front of the radiator, the A/C compressor, and the oil pan need to be removed?
(5) - Can it be replaced from the top or does the car need to be lifted to get to the underside?

Any advice is welcome.

Mike confused:confused

 

[David-F]

Can you do it your self at home with out a lift, yes but you will need a good jack. It realy helps when tring to do it correctly to remove the oil pan when removing the front timing cover. You will need a puller and installer for the balancer which will probably also need to be replaced(at that age it makes no sence not to while it's off) as well as the water pump. The radaitor willl have to be removed ut you should be able to just lift up and out of the way with out discharging the freon. The intake will have to be removed and if you have never done a tune port before it helps to get a hole of an extra long T40 bit to help at getting the lower runner bolts. You will also have a lot of clean up to do. But this can all be done at home but it will take time that's why it is expensive to have done, time is money.

David Fulcher

 

[rrubel]

One more thought - since '85's use flat-tappet cams and lifters, the lifters essentially become mated to the corresponding cam lobe. You'll also have to replace those with the new cam, but that's only a cost issue because you've got to remove them to take the cam out anyway. Then you'll also need to keep track of which pushrod and rocker arm came from which valve, too, because those ALSO become mated to the corresponding part.

If you're doing this on a budget, just buy stock replacement items. Otherwise, you'll find yourself replacing the cam with something hotter, which means you'll want roller rocker arms, which means you'll need those as well (figure $300 a set) and new pushrods, and then you'll find your valves need work too, so you'll pull the heads to do those and then realize that while the heads are off you might as well port and polish them, or buy new aluminum ones, and by then you're hitting the limit of your intake, so it's time for a Mini-ram, and pretty soon you're $5k in the hole.

So don't be tempted to buy any performance stuff unless you're going to go whole-hog. The ONE possible exception would be to get roller rocker arms and new pushrods, or get take-offs from an LT-1 engine for cheaper. That'll give you a couple more HP at the high end.

[RICHR]

 

[jmccloud]

Cam replace

Two kids in college? Feel for you; been there.
How many miles on your Corvette?
For the kind of $ and effort you're going to spend on a cam replacement, you can get some serious crate engine (tall block) NEW parts.
In the old days (60's or thereabouts), there were a lot of cam failures due to improper hardening. It always involved the back lobes (7 sometimes but mostly 8). If the back lobes went, a replacement cam was called for. If it was any other lobe, it was usually a lube circulation problem and the block needed close attention.
In your shoes, I'd look really long and hard at a tall block.
Good luck
PS Both of my kids have 'lived at Dad's' with their families once and are now supporting themselves with 11 wonderful kids of their own. And I have enough dough to support my Corvette.
Hope you get there.

 

[Edmond]

They quoted me $4300 for an engine rebuild (which they recomend) and $2700 to replace the cam shaft.

For those bucks, I'd learn how to do it.:L

A ZZ4 motor would be an ideal stock-like motor with a little more oomph. Make some friends who know how to do it.:cool

 

[mdsbch]

Thanks for all the info and advice. I've decided to do it myself after talking to one of my club members that has done a few and is willing to help. The car has 100,000 miles on it and other than the bad lobe (#2 exhaust) it runs very smooth as long as I don't step on it under load where the rpm gets over 3,000. I will be replacing the camshaft, lifters, timing chain / gears, and probably the water pump. I hadn't thought about the balancer, but i will look into that too.

Mike

 

[grumpyvette]

you can replace the cam and lifters for well UNDER $300 in a single weekend in your driveway or garage with zero special tools, Id advise getting a CRANE 114122 as its an easy 30 extra hp with zero problems, 100% compatable with the stock engine and programing and passes emmission testing easily

http://store.summitracing.com/partdetail.asp?part=CRN-114122&autoview=sku

http://store.summitracing.com/partdetail.asp?part=CRN-99002-1

http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_10002_746091_-1_10241

http://www.helminc.com/helm/Result....dule=&mscsid=P1AF5BUECLLM8H0L8P8GCXMVSRD13801

if you were closer Is say bring it over here!

 

[rrubel]

Don't forget to soak the new lifters in a can of clean oil for a couple days so they are inflated when you install them...
[RICHR]

 

[mdsbch]

Thanks. I haven't opened it up yet, but discussed it with a club member that works for GM and he thiks it may only be a weak lifter, so I may not need to tear it down that far. If I do end up replacing the camshaft, gears, chain, and lifters. I will defintely use prelube and soak them, since I've seen several articles about destroying brand new camshafts due to not properly lubing them and following the break in prcedures. Thanks for the info about the Crane cams. I am trying to keep it as close to stock as possible, but was very confused when looking at the different camshaft specs.

Mike

 

[grumpyvette]

the crane cam I suggested is just slightly larger in durration and lift than the stock cam, but its enought larger to give a noticable boost without getting into any emmission testing, tunning or drivability issues

btw

http://www.geocities.com/MotorCity/Downs/3000/cmspec.html

http://www.engineparts.com/motorhead/techstuff/stockcspecs/chevrolet.html

http://www.nastyz28.com/sbchevy/sbccams.html

 

[Hib Halverson]

Here's the straight story on this.
If the engine does, in fact, have a worn or "flat" lobe, that means a lot of powdered metal has probably gone into the oil and through the engine. Generally, residue from a cam and lifter failure does the most damage to piston skrits and bearings.

If this engine has been this way for a while, ie: the cam lobe has slowly worn down to the base circle or near so, a lot of very fine, abrasive material has gone though the motor. If there's enough of it, it's probably clogged or partially clogged the oil filter and once the oil filter bypasses, the metal particles go round and round and round though the oiling system never being trapped by the bypassing filter.

I'd get the motor out and tear it down. Look closely at bearings and piston skirts then cut the oil filter apart. If there's lots of evidence of fine scoring of bearings and piston skirts and the inside of the oil filter has some fine, pasty looking metallic stuff, overhaul the engine.

If you tear down and find little or no evidence of metal particles damaging bearings or piston skirts, then measure the bores. If the bores are tapered beyond limits, overhaul the engine. If the bores are not tapered or tapered within limits, then you might be able to get away with a "cheap rebuild", ie: disassemble and clean everything. Bottle brush hone the bores. Install new bearings, rings and a new cam and lifters. Give the heads a valve job (replace valve springs, pushrods and rockers as necessarly) then reassemble the motor.

 

[grumpyvette]

what HIB Halverson said is 100% ON
thats one reason IVE ALWAYS STRONGLY SUGGESTED YOU

add a few magnets to the oil pan and drain back area in your engine, the trap and hold metalic dust that comes from wear and increase engine life span by preventing that crap embedding in the bearings
http://www.kjmagnetics.com/proddetai...d=D66SH&cat=13
http://www.kjmagnetics.com/proddetail.asp?prod=D66SH

The SH material in the D66SH magnets, means that the magnets can be heated to 300° F without any loss of magnetic strength, unlike standard neodymium magnets that begin to lose strength at 175° F. Suitable for many high temperature applications.



these are even more tollerant of temp swings and retain strength at even higher engine oil temps plus they are smaller and easier to use, THEY TRAP AND HOLD AN AMAZING AMOUNT OF CRUD! especially if you use several in the oil pan and lifter gallery and heads in drain back locations

 

[CAJUN C4]

you can replace the cam and lifters for well UNDER $300 in a single weekend in your driveway or garage with zero special tools, Id advise getting a CRANE 114122 as its an easy 30 extra hp with zero problems, 100% compatable with the stock engine and programing and passes emmission testing easily

http://store.summitracing.com/partdetail.asp?part=CRN-114122&autoview=sku

http://store.summitracing.com/partdetail.asp?part=CRN-99002-1

http://www.jegs.com/webapp/wcs/stores/servlet/product_10001_10002_746091_-1_10241

http://www.helminc.com/helm/Result....dule=&mscsid=P1AF5BUECLLM8H0L8P8GCXMVSRD13801

if you were closer Is say bring it over here!

Grump:
I bet all of us wished that they lived close to you.You can't imagine how many of us that you've helped over the years
From all of us just Thanx
CAJUN C4 (Dennis)

 

[grumpyvette]

Im always glad to help nice people with thier corvettes, you would be amazed at the long term benefits you see from helping others

 

[CAJUN C4]

Im always glad to help nice people with thier corvettes, you would be amazed at the long term benefits you see from helping others

Amen

After all ...Isn't it why we are all here in the first place.

 

[vetteboy86]

Other then what the shop told you, what evidence do you have that there is mechanical damage? I would investigate things a little more. Pull the valve covers and turn the motor over by hand and watch the rockers arms.

 

[speedmaster4]

$4300 for rebuild, $2700 for a cam change = criminal...you can have a complete NEW 350 iron head engine, built by GM, with warranty, for under $2000, on your doorstep...see latest Jegs catalog...even cheaper if you have a (real) friend at the local dealership...if you don't want to be bothered, just open your wallet, lean back and enjoy it.

 

[mdsbch]

Well, I pulled the valve cover on my 85 Coupe and measured the movement on the #2 pushrod with the rocker off and it barely moved (maybe 1/16th in if that), so it looks like I will be replacing the camshaft . I'm going to replace the timing chain and sprockets also. I've heard that the cams made overseas aren't as good a quality as the ones made in the USA. Does anyone know how I can find out which ones are mad in the US (Summit, Crane, Comp, Edelbrock, etc.)? I would like to keep it as close to stock as possible. Currently I'm looking at a camshaft kit and timing kit from Summit :confused.

Camshaft Kit - http://store.summitracing.com/partdetail.asp?part=SUM-G5000&autoview=sku

Timing Kit - http://store.summitracing.com/partdetail.asp?part=SUM-G6600&autoview=sku

Has anyone used these? Is the roller type timing chain better and will it work without having to replace the cover or make any other mods?

 

[CAJUN C4]

That's a Perfect Cam / Kit for your 85' Smooth Idle good vacuum etc.

Don't forget the Roller Rockers..good for another 15 HP or so.

 

[mdsbch]

Does anyone know what the specs are for the stock engine in the 85 corvette (5.7L TPI)?

Duration Intake / Exhaust ?
Advertised Duration Intake / Exhaust ?
Lift in inches Intake / Exhaust ?
Lobe Seperation ?

Thanks!

Mike