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Yikes! Help!

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spyderxlt

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Alright, so I am the "once" proud owner of a Bayliner 192 Cuddy with the Mercruiser 4.3L/262... I say "once", because it has been pissing me off lately. In any case, my problem is this: I installed the intake manifold and torqued the first bolt in the sequence to 35 lb-ft, as specified in Mercruiser Service Manual 25, Page 3A-25, Paragraph 4. Apparently this was a bit too much!? The first bolt held, however the second one snapped off around 25 lb-ft. FML, right? So, I removed the manifold again, and extracted the bolt (pain in the A!) and am ready to try again. After re-verifying the manual (which does in fact say 35 lb-ft), I noticed a table on Page 3A-2 that states that the intake manifold bolts should be torqued to 11 lb-ft! WTF? There's a HUGE difference between 11 lb-ft and 35 lb-ft! The manual contradicts itself! I don't want to snap another bolt, as they are $5 a pop... So, question, what is the PROPER torque for the 4.3L intake manifold bolts (8 bolt manifold)? Will 11 lb-ft be sufficient to prevent water and exhaust leaks? I'm weary about torquing to 35 lb-ft again. Anyone got a straight answer?

On another note, my 4.3L has a balance shaft, which leads me to believe it is the Gen+. Am I correct?

-SpyderXLT
 
First off... when assembling anything with fasteners...

1) Make sure you fasteners are clean, and the threads as well as the load bearing surfaces of the nut and bolt (as applicable) are in good shape. Also, make sure they are the right fasteners (material and grade). Home depot is NOT the right place to buy replacements. Correct size and thread pitch is but only one factor of many. Especially for this example... the 'bolts' you are installing aren't actually bolts, they are capscrews. Bolts are typically machined to a class 2 fit. Capscrews are machined to a class 3 fit. If you are putting a bolt in the hole where a capscrew belongs, there is a looser fit... less frictions... keep reading.

2) Use the correct thread lubricant. Since most of the final torque is taken up by overcoming friction, using the right lubricant is crucial to achive the right clamping force. If no lubricant is specified, no lubricant is what is expected. If you lubricate a fastener in this case, you'll almost certainly break it before it reaches final torque. If you take too much firction out of the picture, too much clamping force is generated... if that force exceeds the yield strength of the fastener... snap.

3) Install all the fasteners hand tight, making sure whatever it is your assembling is properly situated.

4) Divide your final torque by at least 3.... that's your first torque increment. Use the correct torque secquence specified in your manual. If the manual doesn't specify, use a star pattern, or for fasteners in a straight line work from the center of the assembly outward, swapping sides as you go.

5) Double your first torque increment.... that's your second torque increment. Use the same torque sequence as above.

6) If you divided by 3 above, now go to your final torque. Otherwise continue with reasonable increments until you get to the final torque. Use the same torque sequence as above.

7) Complete at least 2 more check passes at final torque. As the clamping force stabilizes and the assembly gets situated in place, and whatever gasket gets to the right amount of compression, fasteners will tend to become loose. This is especially an issue where any metalic type gasket is utilized in the joint. If this is the case, wait about 10 minutes and do at least one more check pass. Keep doing check passes until you go through a complete pass on all the fasteners and there is no movement in any of the fasteners during that complete pass.

One other thought to the snapping of your first bolt... are you using a 'clicker' type torque wrench?
IMO, those things are junk. To be anything close to accurate, they need to be exercised several times in both directions at the torque value your trying to apply. Which means a trip to the vise everytime you move on to tighten a fastener to a different torque.
I prefer the dial indicating type.

WRT the required final torque, I don't have the manual for your engine... I'm sure one of the regulars on this site will get that for you.
 
Sorry guys TMI.

I have installed so many intake manifolds in my life I cannot count them, here is the way it's done in the profession. Coat your gaskets intake ports and water cross with black rtv. Start all your bolts by hand. Get a nice Snap-on 14mm or 9/16 box wrench and start on the center bolts, snugging them down going from bolt to bolt in a circular motion from the center out. When you get back to the starting point, these bolts will be loose again. Repeat this step over and over until the bolts are tight. You should make the bolts about as tight as you would the thermostat housing. Forget about the torque wrench. Works on the old style intakes as well as the Vortec.
 
docksidemarineservices said:
sorry guys tmi.

I have installed so many intake manifolds in my life i cannot count them, here is the way it's done in the profession. Coat your gaskets intake ports and water cross with black rtv. Start all your bolts by hand. Get a nice snap-on 14mm or 9/16 box wrench and start on the center bolts, snugging them down going from bolt to bolt in a circular motion from the center out. When you get back to the starting point, these bolts will be loose again. Repeat this step over and over until the bolts are tight. You should make the bolts about as tight as you would the thermostat housing. Forget about the torque wrench. Works on the old style intakes as well as the vortec.
Click to expand...


ditto!!!!!!!!!!!!!!!!!!!!!
 
Agree with both Bt Doc and Troy..... and I must confess, Chris has it right also.
I too can't recall using a torque wrench on these particular bolts...... but much of this comes from years of experience.

Whether or not you purchased these bolts from Mercruiser, be sure to check the symbol of each bolt head.
The bolt grade will be incoded in this symbol.
If the grade is not adequate, it may explain why you snapped the bolt(s) and were able to extract the broken portion (and apparently with some ease).
This may suggest that the bolt yielded, apposed to thread gawling or jamming.

Here is a loose guide for grade 2, 5 and 8 American fasteners that will give you an idea of the different values per grade.
Correct bolt length and thread length will be important as well.

In extreme technical terms, engineers will spec torque values for both wet and dry threads.
You may want to lubricate the bolt threads.... (see Troy's #2) .... even if Permatex (or equivilant) will be acting as both sealant and lubricant.
However, this may require a reduced final torque value....... (again, see Troy's #2).
Torque value can be checked and re-set after the engine has undergone a warm/cool cycle..... favoring warm for setting the final value.

But again, Ditto Chris's comment.

.
 
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And the best part using Permatex Aviation is that it can be used everywhere, brass, steel, copper ,head bolt sealant, manifold, exausts, anyplace a sealant is required. Best stuff going.
 
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