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38 V6 camshaft

R

rosbullterrier

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I'm concerned with the cam

I'm concerned with the camshaft installation in a 1981 GMC 3.8 V6.
There doesn't appear to be anything to keep it in place! So far I've only attached the timing chain on crank/cam wheels - the camshaft can flop forward a little towards the timing cover.
Does the distributer and oil pump drive keep it in place? There's nothing to stop it moving as far as sideways movement in the timing chain allows!
 
"Andrew, in short....... and i

"Andrew, in short....... and if this is a flat tappet camshaft engine, Yes... you are correct!

You will notice that the inboard side of the cam chain sprocket will have what appears to be a thrust surface that mates to a like surface of the block. This surface will counter the thrust of the oil pump drive gear! The camshaft should not walk forward! "
 
Is this the Buick V6??? Some o

Is this the Buick V6??? Some of the earlier cars equipped with this engine had a spring and a button at the front of the camshaft which pushed against the timing case cover and kept the cam in position...not sure about the marine versions.
 
"Thank you for advice gents. I

"Thank you for advice gents. It is the Chevy engine; the distributor/oil pump cam drive are through the manifold at the rear, the fuel pump drive at the front.
I had already built the other side engine and could not remember similar movement, must not have moved the block end up!
Yes the inside of the camshaft cog has small raised pads which bear on the block. I shall now finish the build.
Dare I voice opinion: the Selec Manual, which is all that available in GB is in parts, incorrect, very repetitive, fuzzy pics, incomplete, and not methodically structured for practical problems . . ."
 
"The OMC manual is not great f

"The OMC manual is not great for the 229. Get the Mercruiser one. When it comes time to time the distributor, the OMC manual has the wrong procedure and gives you a 50/50 shot of damaging the engine. You need to start reading from page 4B-3 from Mercruiser manual #7 for the Mercruiser MR185/MCM185 unless you want to risk melting pistons.
The Mercruiser 229 manual can be d/l for free here:
http://www.4shared.com/file/121507388/2e92adf3/MercruiserManual7.html

The 200/229 Chevrolet 90 degree V6 has a firing pattern like no other automotive or marine V6 ever made...so finding #1 on the distributor requires additional knowledge. You can't just pick any starting point for #1 like other engines. "
 
"[b]Quote: "so finding #1

"Quote: "so finding #1 on the distributor requires additional knowledge. You can't just pick any starting point for #1 <font size=""+1"">like other engines."</font>

HyStat, Just curious, as I understand the unequal cylinder crankshaft angles, the Odd range of Point "Break" and Dwell Angle, and the caution as to the starting point of the distributor "point cam" for # 1..... that would be very critical for Andrew to know about!
I fully understand why you mentioned this.... Great Point! (no pun intended)

Aren't these distributor caps indexed to the distributor housing, and clearly marked as to cylinder #'s?

Also, if I read the advance curve/graph correctly, it appears to show a TA of approximately 32* @ 3,500 rpm...... is that what you see?
(20* mechanical + base of 12* = a TA of 32* @ 3,500 rpm)

."
 
"[i]Aren't these distribut

"Aren't these distributor caps indexed to the distributor housing, and clearly marked as to cylinder #'s?

The prestolite caps are never marked, nor are the Sierra prestolite ones. so after indexing to the proper shaped lobe, you want to mark the base before installing the cap for reference.

I can't remember how much advance I saw last time I had a light on my 3.8"
 
"[b]"Does the distributer

""Does the distributer and oil pump drive keep it in place? There's nothing to stop it moving as far as sideways movement in the timing chain allows!"

"Andrew, in short....... and if this is a flat tappet camshaft engine, Yes... you are correct!"

Ayuh,... Actually,.. That's Incorrect...

The cam/ distributer gear would turn to Dust if it was correct...

The cam is located in-place by the slight bevel of the cam lobes,+ the pressure of the lifters pushing on 'em...
The cam lobes are slightly beveled from front to back, causing the cam to ride against the thrust bushing...

Not trying to start an arguement, just setting the record straight...."
 
"[b]Bondo, I'll argue the

"Bondo, I'll argue the point in a gentlemanly fashion here, and for the sake of conversation only!

First things first, however:
Quote:"The cam/ distributer gear would turn to Dust if it was correct..."
Bondo, whether or not the cam is being pulled rearward, or remaing neutral or being mildly pushed forward (by this gear set.....), the thrust that the two "drive/driven" gears undergo alone would cause the "Dust" if this were an issue!
I don't know the actual force required to hold a flat tappet camshaft in center position.... but I do think that these two gears are part of the design equation. Yes/No?

OK, on to the topic:
Pull an old camshaft out and take a close look at the "drive" gear, and then look at the "driven" gear of a distributor for the same engine....... and then consider rotation!
Examine the effects that the drive gear has on the lateral movement of said camshaft while under the load of driving an oil pump! (for this, look at the wear pattern on the two gears)

And as you know, the actual flat tappet cam followers (lifters) are never centered on the actual cam lobe. This is what causes them to rotate and may add additional lateral force to the camshaft. I don't know.... you may be correct on that issue!

Bottom line..... I'd be inclined to think that a camshaft, while driving an oil pump (via hypoid gears), would have less tendancy to walk foward! Yes/No?

."
 
"[b]"And as you know, the

""And as you know, the actual flat tappet cam followers (lifters) are never centered on the actual cam lobe. This is what causes them to rotate and may add additional lateral force to the camshaft. I don't know.... you may be correct on that issue!"

Ayuh,... Look at the lobes of a flat tappet cam,...
The lobes are taller at the front,+ shorter at the rear...(by a few thousandths)
That is what causes the lifters to rotate, as well as the force which keeps the camshaft in place....
Or,...
Put a set of roller lifters into a motor with a flat tappet cam,...
The cam gear,+ distributer gear will turn to dust, as the cam walks out the front of the motor...
"Bottom line..... I'd be inclined to think that a camshaft, while driving an oil pump (via hypoid gears), would have less tendancy to walk foward! Yes/No?"

Nope,... If that were true, we wouldn't have to use thrust buttons on roller lifter motors...."
 
"Bondo, I don't disagree w

"Bondo, I don't disagree with you on that..... I think you are correct. I just can't discount the additional pull/thrust that the two gears would apply.

As for roller cam followers...... the later SBC uses a camshaft thrust plate to counter any forward "walk" of the camshaft. I'm thinking that buttons were used on the earlier engines.
Yes/No?

."
 
"[b]"As for roller cam fol

""As for roller cam followers...... the later SBC uses a camshaft thrust plate to counter any forward "walk" of the camshaft. I'm thinking that buttons were used on the earlier engines.
Yes/No?"

Ayuh,... The New blocks use the thrust plate to locate the cam,...
Retrofitting an older block requires a cam Buttom to locate the cam...

As for the pull of the distributer gear,...
How much could a little iron gear pull, Vs. 16 plungers pushin' forward on 16 little ramps provide..."
 
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