Torquing connecting rod cap bolts on 1993 Merc Force 90 HP

Hello everyone,

I recently purchased a 90HP engine that has less than 100 hours on it, but the #2 piston had a head gasket blow, and subsequently the top ring got sheared in the exhaust port, then the engine sat in storage (on the original boat) since 1997 (18 years).

Instead of doing a full teardown on what is essentially a new engine, I decided to go in through the reed-valve openings and pull the piston out that way. All has gone well so far except...

When I tried torquing the connecting rod cap bolts, after the initial torque (15 in-lbs) and alignment check, I can't seem to achieve final torque (30 ft-lbs or 360 in-lbs) and the bolt seems to be easier to turn. I also did not get the socket all the way on the other bolt as I was torquing it and partially stripped the head.

In all my other engine work (which is not tons), I have never run into stretch-bolts as far as I remember.

My questions are:
- is 30 ft-lbs the correct torque for this engine? (serial 0E019700)
- is 360 in-lbs the same as 30 ft-lbs?
- are there more specific steps in torquing the connecting rod cap bolts?

My confidence is waning,

- Jeremy

30 X 12 is 360.-------Shortcuts do not always work !!

Thanks racerone.

Yeah, I hope this won't be a complete teardown, but it might be.

My plan now is to pull the piston back out, clean everything up and try again. I bought a bunch more bolts that came in today, so I should have a few tries. I think part of the issue is cheap Chinese parts, I have had to get replacements for parts I ordered twice now (a missing roller for the one bearing and rollers that were just slightly too big for the wrist-pin bearing, along with two used refurbished connecting rods that didn't exactly meet my standards.

I do have a local mechanic who is willing to help out, but he is flat-out busy, so I won't be able to get his help until mid-July at the earliest.

- Jeremy

Ok, so I am back from holidays.

I just tried torquing some of the connecting rod bolts on a rod outside of the engine just to get a feel for it (I ordered a few extra bolts).

I have managed to break two of the bolts I have, but they never got up to 30 ft-lbs, the most I was able to achieve was ~23 ft-lbs. I was using a clicker inch-lb torque wrench for the first one, but it never clicked, so I went to my trusty old ft-lb torque wrench (not a clicker) and managed to get it up to about 23 ft-lbs before it started slacking off, eventually breaking after it went less than 20 ft-lbs.

In all the manuals I have looked in, I can only find final torque of 30 ft-lbs, but based on the five bolts so far that I have attempted to torque, this seems too high. these bolts have a 1/4" 12-point head on them.

REQUEST: Could someone look up the torque for the connecting rod bolts for my engine to see if I have been looking at the wrong specs? It is a 1993 Mercury Force 90HP serial 0E019700

- Jeremy

While your FORCE was sold by Merc it is not a Merc powerhead, they cobbled it together with some Chrysler, US Marine and Merc discontinued parts. And the 90 horse models were some of the most "cobbled together" models of the entire Force line - I counted once and there is close to 100 distinctly different versions of the 90 horse Force, and not all parts are interchangeable.

You might get a better answer if you post your question in the FORCE part of this forum.

The only info I have is on 90 horse Merc's and for that model year the procedure is to tighten the bolts finger tight, then torque to 15 inch pounds (and check alignment), then 15 foot pounds, then 30 foot pounds, then a further 90 degree turn with the socket to finish up.

If you are busting off the bolts at 30 foot pounds it sounds like you didn't get engine grade bolts (or there was a really bad batch) because 30 foot pounds is really not a lot of torque...

Your way over torqing!!! Here is spec's......

SETTINGS FOR 3-4-5 CYLINDER THRU 1995 MODELS

CYLINDER HEAD BOLTS 225 IN. LBS.
FLYWHEEL NUT 90 FT. LBS.
MAIN BEARING BOLTS 270 IN. LBS.
CONNECTING RODS SCREWS 170 IN. LBS.
POWER HEAD MOUNTING BOLTS 270 IN. LBS.
EXHAUST PORT COVER BOLTS 70 IN. LBS.

Thanks Graham, that was the only info I could find for the procedure as well... I may post on the FORCE forum if I cannot find the correct info in a manual of some sort. I will try to look in the Chrysler manuals and see what they have to say.

I see there is another response after yours that says 170 in-lbs (14+ ft-lbs), which would make more sense with the size of the bolts and what I am experiencing with torque-up.

- Jeremy

That is quite a bit different faztbullet, thanks so much for the info.

I will try to find a manual for that. Am I safe to assume the procedure for the connecting rod cap bolts is essentially the same? i.e. finger tight, check alignment, little torque, check alignment, half torque, check alignment, full torque, check alignment, add 1/4 turn after final torque. with loctite and lube under the bolt head of course.

Is there anything else I need to watch out for while re-assembling? Once the connecting rods are back in, I basically just have the head to torque down (following the correct sequence which I need to find and re-torquing after a heat cycle), the reed valves and carbs to put back on.

Cheers!

- Jeremy

Another case where religious use of a torque wrench resulted in disaster. I too always use one for rod bolts, but one needs to be careful.

Jeff

Just install the new one with drop of oil on threads,hand tighten to align, torque to 50inlbs,check alignment then takr to 100inch and finish at 170inlbs and no 1/4 turn.!!!

Hi Faztbullet,

so I take that to mean no loctite either? just oil? That would seem to coincide with the Chrysler manual I was looking at - instructions were much less detailed in there as compared to the merc manual, so I wanted to be sure.

Thanks again for the info.

- Jeremy

fastjeff said:

Another case where religious use of a torque wrench resulted in disaster. I too always use one for rod bolts, but one needs to be careful.

Jeff

Click to expand...

Yes 8-|. it also helps to have the correct torque info. I knew something was not right, but all I could find previously was the 30 ft-lb spec which is obviously not correct for this engine.

- Jeremy

Well Gentlemen,

Thanks for all your input. I managed to get things back together yesterday evening and she fired up right off the bat (after cranking with the ignition off for about 30 seconds total just to make sure there were no major problems before firing).

Head torque stayed pretty tight after the first heat cycle, only minor movement for a few of the bolts to bring them back to spec.

Now to change out the lower unit oil, flush and re-install the fuel tank along with a new fuel filter/water separator I bought and I should be ready to take her for her first test run on the water.

- Jeremy

One other question, not related to torque...

When I purchased this boat, the powerhead was partly dis-assembled. There is a hose barb on the bottom of the "intake manifold" that I am unsure what to do with as there was nothing connected to it. is it simply a breather or drain? do I need to connect a fuel line to it and route it somewhere? does it need a check valve?

- Jeremy