1988 Volvo MD31A Exhaust Bolt Torque Specification ?

[Fritz Lang]

I have a MD31A Volvo engine, 1988. Replacing seals. What is the proper torque for the mounting nuts ??
Thanks.

 

[Fun Times]

Hi there Fritz Lang , welcome to iboats.

If you don't happen to have a Volvo Penta service manual on hand for your engine model to help with the torque specifications, then another method you could try using is if either the bolts happen to have a number/sizing sequence on the bolt head or by way of you measuring the bolt diameter; 'Then using the scale below, should be able to help you transfer the bolt measurement sizes into a pretty close torque spec for you to go by.

http://forums.iboats.com/forum/engin...14#post3838214

Tightening Torques: Tightening torques for vital joints that must be tightened with a torque wrench are listed in work-shop manual “Technical Data”: “Tightening Torques "and are contained in work descriptions in this Man-ual. All torques apply for cleaned threads, screw heads and mating surfaces. Torques apply for lightly oiled or dry threads. If lubricants, locking fluid or sealing compound are required for a screwed joint this information will be contained in the work description and in “Tightening Torques” Where no tightening torque is stated for a joint use the general tightening torques according to the tables below. The tightening torques stated are a guide and the joint does not have to be tightened using a torque wrench.
Dimension, Tightening Torques
Nm. lbt.ft;
M5, 6. 4.4;
M6, 10. 7.4;
M8, 25. 18.4;
M10, 50. 36.9;
M12, 80. 59.0;
M14, 140. 103.3;
Though this is not for your engine, page 7 can be used a general guide for how Volvo goes about Repair instructions, https://www.scribd.com/doc/94969381/...Service-Manual

 

[Fritz Lang]

Thank you, but I saw this table. Do you have confidence that such generality is applicable ?? When taking the manifold off - all the nuts came off with the same torque (my feel) - indicating that someone cared about the tightening torque when last assembled.

 

[tommarvin]

Fritz, , Fun Times just tried to help you.If not get a service manual.

 

[Fun Times]

Being that you're not torqueing down extremely vital internal engine components such as heads, rods, etc. that you normally wouldn't have easy accessible access to for general re-tightening maintenance purposes, Yes in this particular case of not having the exact specs you're looking for, I would feel more confident using Volvo Penta's suggestion of using their chart they've always been putting near the beginning pages of all their service manuals that I've had the opportunity to read over the years.....Plus bear in mind that as an annual tightening maintenance item, it's typically suggested to check all accessible nuts, bolts, hose clamps, etc. which would include exhaust bolts as well.

Being your engine has studs on the engine side and uses flange nuts to hold down the exhaust manifolds, a lot of service personnel out there would probably just end up using what is described as a calibrated elbow gained from general experience of not over or under tightening the nuts....In turn going by very careful feel for an even torqueing.
https://www.marinepartseurope.com/en/volvo-penta-explodedview-7745620-26-19153.aspx

All that mentioned, The general average for gas engines tend to be around the 25 lb.ft range for the manifolds if that helps you out any.

From a Merc 4 cylinder service manual: Step 2, Tighten fasteners evenly and torque to 23 lb. ft. (33 N?m), starting in center and working out toward ends.

 

[Chigwalla]

Right out of the VP manual for the MD31A:

"External components

27. Install the exhaust manifold with new gaskets and the
thermostat housing. (Locate the cable harness between
the thermostat housing and the water circulation pump.)
Install the oil dipstick.

Were it critical, the torque spec would be in that paragraph, since VP puts them inline in the text instead of a separate table at the front of the section like Merc does. The fact that it's not there means you default to the table that FunTimes posted above.

... would probably just end up using what is described as a calibrated elbow...

Only your elbow is calibrated in ft*lbs. When you're working in inch*lbs, it's a calibrated wrist.