Torque specs for head bolts on a vintage 18-20hp OMC motors

[kfa4303]

HI all. Just wondering if any one has the torque values for the head bolts on a '60s era18-20hp OMC outboard. I'm about to install a new head gasket, but want to be sure of the specs. Also, should I follow a break-in procedure after the job, or can I run the motor normally? Thanks.

*the motor is a '66 FD-20C, 20hp Johnson. Head gasket is part #322332.

 

[AlTn]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

factory manual.. 1965-18 hp. fastwin 18502,18503...calls for 96-120 INCH pounds....however...mechanic at the local dealer told me he takes the 1/2" head screws to 16 ft/lbs, then to 18 ft/lbs after a couple of heating/cooling cycles...sounded too tight to me but, I torqued the last 25 hp. < 1972 > to 16 ft/lbs, so far so good...might want to wait for the more experienced opinions

 

[gm280]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

HI all. Just wondering if any one has the torque values for the head bolts on a '60s era18-20hp OMC outboard. I'm about to install a new head gasket, but want to be sure of the specs. Also, should I follow a break-in procedure after the job, or can I run the motor normally? Thanks.

*the motor is a '66 FD-20C, 20hp Johnson. Head gasket is part #322332.

Torque lb/fts is important but sequence is as important as well. If you don't have the sequence available, then start in the middle bolts and work around the bolts in a clockwise configuration as you move out to the further bolts. In other words start in the middle then across from that bolt then across from that second bolt to the side you started on but one bolt out from that first bolts. Sounds crazy to wexplain but if you could see the pattern then it would make perfect sense. And after a few heat/cool cycles recheck them again using the same sequence pattern too... If I can figure out how to copy the sequence pattern from my Johnson shop manual I'll post it...

 

[HighTrim]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

Here is the sequence, but exactly as described above. When in doubt, start in the middle, and spiral outwards.



The following chart will be helpful as well



Start with half torque value for a cycle, then 3/4 torque, then the final torque. After running and bringing to temp a couple times, re torque in the same fashion. Then you're all done.

OMC Gasket Sealing Compound on the threads. Be sure to dress the head, I dont think I have ever found one straight!

 

[kfa4303]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

Update: Hi all. After a trip to the shop to have some stubborn flathead bolts removed, I finally got the power head taken apart and ready to reassemble. For my first major "brain surgery" on a motor it went surprisingly ok. It's cool to see how all of the inner passages really work inside the powerhead. Even though it's still old/ugly on the outside, the inside of the motor looks great. I've gone through several cans of lube in order to clear out all the water cooling passages as well as clean up 50+ years of carbon build up and goop, but the cylinders are in great shape and the rings still bounce nicely. I even went got all new stainless replacement hardware that will make any future repairs much easier. Now that everything has been thoroughly cleaned and reconditioned, I'm ready to put it all back together (I think). Does anyone know if West Marine carries OMC gasket sealing compound, or can I Permatex Ultra Black, or similar product in its place? Also, are there any other bolts I need to apply it to besides the head bolts (i.e. the fuel bypass bolts, exhaust manifold bolts, etc...)? With any luck the old girl will be running in the tank tomorrow and perhaps even the open water by weekend (jinx). I'll try to post pics tomorrow.

P.S.
Once the new head gasket is installed will I need to follow a break in procedure, or just run it as usual, then re-torque the head bolts after the first trip.

 

[HighTrim]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

Regarding break in, did you change the rings and hone the cylinders? What exactly was done internally?

The head bolts will have to be retorqued after getting heated up a couple times in the same fashion as before.

 

[kfa4303]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

No, I left the internals intact. I'm just replacing the various gaskets in the power head. I did some more reading last night and saw that several folks here in the forums use Permatex Aviation gasket maker on the head bolts. I actually have some from a previous job, so I'd like to use it if possible.

 

[kfa4303]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

Here is the sequence, but exactly as described above. When in doubt, start in the middle, and spiral outwards.

View attachment 194133

The following chart will be helpful as well

View attachment 194134

Start with half torque value for a cycle, then 3/4 torque, then the final torque. After running and bringing to temp a couple times, re torque in the same fashion. Then you're all done.

OMC Gasket Sealing Compound on the threads. Be sure to dress the head, I dont think I have ever found one straight!

Just to confirm, according to the chart my 20hp is essentially equivalent to the 18hp Fastwin which has the head bolts listed at 120 in./lbs = 10ft./lbs. Is that correct?

 

[HighTrim]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

That is correct.

 

[kfa4303]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

Awesome! Glad I can still divide by 12.

 

[kfa4303]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

So I went and got a nice shiny new torque wrench for the final tightening of the head bolts. As I approached the 10 ft/lbs spec, some of the bolts certainly got tighter, but others fell like they will not tighten anymore, or may strip if I go any further, and I never heard the tell-tale "click" it's supposed to make when it hits the preset value :/ I'm new to torque wrenches, so I'm not sure what 10ft/lbs should "feel" like. I know that's somewhat subjective, but I don't want to over tighten the bolts. Can I practice on a nut on say my trailer hubs, or would 10ft/lbs be too much? Otherwise, the motor is running better than ever. It starts with one pull, idles nicely and just seems generally smoother and happier. I'd like to leave it as is, but I don't want the whole thing to go kablooey on my first long WOT run either. Thanks for any help.

 

[HighTrim]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

If you follow the correct spiralling order, they will all tighten down evenly. That is also why it is good to start with 5 ft/lbs, then 7.5 ft/lbs, then the final 10 ft/lbs. It both helps keep it even, and you are also always supposed to start your torque wrench off on a lower setting, especially when sitting.

Then after a couple runs do it again.

 

[kfa4303]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

Yeah, I've been doing that, but it feels as if a few of the bolts are on the verge of stripping and/or not tightening any further :/ I guess I'll test 10ft/lbs on a separate nut and bolt to see if I can get a "feel" for it. Also, how do I tighten up the head bolts after my break-in runs? Unfortunately, 2 of the head bolts are inaccessible to the toque wrench when the powerhead is mounted in place. Should I re-remove the power head again, re-torque the bolts, then re-re-reinstall the powerhead?
Who ever designed this old girl was drunk as a skunk. Not only are half of the hardware/fasteners inappropriate for the job (i.e. large flathead screws, rather than proper bolts), but 1/3 of then are in accessible when the motor is mounted in place :/ It's worse than a British sports car.

 

[AlTn]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

google...paul moir engine teardown and reassembly shareaproject.com.....at the bottom of the page he gives the equation for calculating the proper torque using an open end wrench in combination with a torque wrench.

 

[kfa4303]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

I have the correct toque spec values (10 ft./lbs.) and procedure for reinstalling the head. That's not the issue. I guess I'm just not sure how much 10ft/lbs. "feels" like. I just tried using the toque wrench on some other bolts to test it, but I couldn't get it to make the tell-tale "click" when it hits the preset value. I tried values as low as 5ft/lbs, which is as low as it can go and still no "click". Is it possible that I may have tightened the bolts beyond 10ft./lbs. by hand, or is that not even possible (I'm 6', 165 and fit)? By means of comparison, how much is a typical lug nut torqued to (+/-) 10ft./lbs. I suppose I could go DIY and use an extension pipe and spring scale, but I have a feeling that wouldn't end well.
I just checked the link you posted AlTn and it looks like the author had the same issues I'm having. However, he mentions the spark plugs on his little 4hp being torqued to a value greater than my head bolts. "To Install the spark plugs. They should be torqued 18 to 20 ft/lbs (twice my head bolt value!?!?), but since the bottom one must be installed with a wrench this will be impossible. Rather tighten the plug until the gasket on it is snug. For fresh plugs it will be quite a bit of turning past finger tight - about 1/2 a turn. You'll feel the crush washer bottom out and the plug will become hard to turn. Stop there. For old plugs you'll have to use your best judgement. But be very careful as it's easy to strip the aluminium threads in these heads." This makes it sound like 10 ft./lbs. is pretty easy to achieve by hand. I guess I'll have to try his two-wrench technique, although removing the power head seems easier at this point. According to his calculations his head bolt torque spec only ends up being 45 in/lbs = 3.75 ft./lbs. ??? I'm assuming this value is actually amplified by the longer lever arm crated by using the two wrenches, but it still seems awfully low even for such a small motor. Are the spark plugs normally torqued to such high values and the head bolts so low? They seem backwards.
Thanks again for all the help.

 

[Tim Frank]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

Range that someone with a manual threw in was 96-120 in-lbs.
That would be 8-10 ft-lbs.
Try for 8?

 

[HighTrim]

Re: Torque specs for head bolts on a vintage 18-20hp OMC motors

For the bottom head bolts I use a crows foot socket on my torque wrench. Google the image and you can see what it will work like. I wouldn't take the powerhead back off.