Question about rebuilding the 3.8

sd_iconoclast

Registered User
I have just finished rebuilding the 3.8 in my SC and I am now installing it in the car. However, I have noticed something that concerns me. It seems that the rebuilt engine is much harder to rotate (the crankshaft) by hand than the old engine. I understand that this is to be expected with an engine with new rings and all, but the new engine is really hard to turn. I have rebuilt a number of engines including V-8s and none of them were nearly as difficult turn. The engine became difficult to turn after I installed the timing chain, tensioner, and timing cover. At first I thought that the timiung cover was somehow interfering with the cam gear or timing chain or something. Then I remembered that the tensioner (I bought a new stock tensioner and chain) seemed to press really hard on the timing chain when I installed it. The tensioner comes with a pin in it that keeps the spring fully compressed until the tensioner is installed.
I now realize that none of the other engines I rebuilt had tensioners. They all had double roller timing chains that did not require tensioners.
My question is: Is this normal? Have any of you guys installed a new chain and tensioner and observed the same thing?
 
Not to be a wise *** or anything but do you have the spark plugs in already? or something covering the holes for them or the exhaust ports?
 
re:

do you have all the main bearing in the right spots? i remember someone saying once that they're are different in certain journals
 
It's very common on these engines to put the main bearings on the wrong jounals. If you do that, it will turn REALLY hard. The different bearings have different thicknesses depending on the journal that they go in.
 
ARV90SC said:
i remember someone saying once that they're are different in certain journals
I was going to say that too, and someone else already has as well. So I'll third it. I do remember that being mentioned. Think it was Mike38SC had replied a while back about this topic of different size main bearing on the back (????) of the crank.
But it seems as you said it was fine UNTIL you put the timing cover on, so I would assume you turned it before the timing chain/tensioner went on?
 
Rear main bearing on 3.8 SC

BobGPz said:
I was going to say that too, and someone else already has as well. So I'll third it. I do remember that being mentioned. Think it was Mike38SC had replied a while back about this topic of different size main bearing on the back (????) of the crank.
But it seems as you said it was fine UNTIL you put the timing cover on, so I would assume you turned it before the timing chain/tensioner went on?

Watch the #4 main on the 3.8 SC... it is deliberately designed .010 under to prevent installing an 3.8 EFI crank into an SC block [factory precaution]
The EFI crank has 2.5190 dia. main journals 1-2-3-4
The SC crank has 2.5190 dia. main journals 1-2-3 and 2.5104 on #4

The bearing insert for #4 main on the SC engine is .1000-.1005" thick while the other three main inserts are .9590-.9650"....

It is possible you may have mixed up the #1 or #2 insert with the #4 inserts

The main bearing are packaged with the #4 inserts at the back of the package.

If in doubt, pull the crank and measure the thickness of each main bearing insert to verify correct placement. You'll need a good set of calipers [digital are best]. Most of them read to four decimal places [.0005"]
 
Didn,t You Platic Gauge

:eek: :eek: :eek: WHEN YOU DID YOUR BEARINGS DIDN,T YOUR PLASTIC GAUGE THEN AS A SAFETY MEASURE??????? :cool: :cool: :cool: ALSO IT SHOULD TAKE AROUND 25-30 FT LBS TO TURN THE CRANK AFTER THE MOTOR IS COMPETED WITHOUT THE SPARK PLUGS INSTALLED.. :rolleyes: :rolleyes: :rolleyes: CHECK OUT AND ENGINE REBUILDING BOOK :confused: :confused:
 
Thanks for the suggestion guys,
However, The spark plugs are not in yet.
The exhaust ports are uncovered.
I checked all bearing clearances with Plastigage.
The crank turned easily until I put on the timing chain and timing cover.
I just wish I had tried to turn the crank after I put on the timing chain, but before I put on the timing cover.
Have any of you installed a new tensioner before? Did it make the engine much more difficult to turn?
 
Last edited:
More info...
I took off the timing cover, timing chain, and tensioner. The crank turns reasonably easily (about what you would expect with a new engine). The cam is really hard to turn. Clearly the problem is somewhere in the cam/valvetrain area. I will unbolt the rocker arms and see what happens.
 
Yet more info...
I took the rocker arm covers off and unbolted the rocker arms. Still the cam is hard to turn. I unscrewed the bolt from the nose of the cam. Suddenly the cam spins freely. I thought that maybe I was missing a spacer or something.
It seems that the cam bolt is clamping the cam retainer plate between the cam (behind) and the washer, distributor (or synchronizer) drive gear, and cam gear in front. I looked at the engine I pulled out of the car, and it seems to have the same arrangement. Any thoughts?
 
I found the problem. It turns out that the cam on the SC is supposed to have a spacer that fits over the nose of the cam, and goes behind the keyway. I missed this because it always looked to my like this spacer was part of the cam itself. In any case, I bought an aftermarket cam and failed to notice that this spacer was missing. The purpose of this spacer is to get clamped when the cam bolt is tightened, thus avoiding clamping the cam thrust plate.
 
Well that was no fun at all, huh? Glad you noticed AND found the problem. Would have sucked if you started it like that. Congrats on finding it. :cool:
 
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