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Bolt confusion for cover assembly on lower unit (Johnson 55HP)

jasondainter

jasondainter

Regular Contributor
Hi Folks.

I have a Johnson 55HP from 1980 (engine model 55EL80C).

I was reassembling the cover assembly (where the shift rod goes through) and retightening all the bolts. In the manual it states 7/16 bolts need 38 to 40 Nm of pressure. So I started tightening to 38, and SNAP, bolt snapped off (so annoying!).

So I figured, well I must have been doing the right pressure, I mean the manual says so, so I tried again on another bolt, SNAP. same thing. 2 bolts down.

So then started looking up the replacement bolt I need, which in the parts manual says its part 307151.

After googling on ebay I find that this is what that bolt is supposed to look like, seems similar in length but the bolt head is chunkier and there is an additional tighetning washer on there as seen below:

OMC-P-N-307151-0307151-screw-for-1968-88-Evinrude.jpg


However the bolts I took of (which I managed to snap 2 of) looked like this below. Similar but thy seem to me to have a less thick bolt head, and they miss that tightening washer part also...

iT2o2Tt.png


So this leads me to believe that possible the bolts I have in my casing might not be original and the previous owner may have replaced them? Could anyone in the know confirm that might be the case? It would perhaps explain why they snapped at the right Nm pressure also.

So i'll have to order 2 more 307151 parts, however I'm confused about one thing. Unless I'm mistaken (which could certainly be the case) It would seem to me that this bolt is supposed to effectively act as a seal between the top of the bolt head and the cover assembly housing. But would the type of bolts seen in the first photo (307151) not create a small gap where those tightening washers go? Im worried if so that water could get into the gearcase as from what I can see theres nothing to stop water getting in other than that bolt being tightened against the casing.

Am I missing something?
 
STOP-----Those are 1/4" bolts.-----Torque on them is 60 / 80 INCH LBS------No wonder they broke.----38 Nm is about 340 inch lbs
 
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racerone said:
STOP-----Those are 1/4" bolts.-----Torque on them is 60 / 80 INCH LBS------No wonder they broke.----38 Nm is about 340 inch lbs
Click to expand...

Just adding for the benefit of the OP ........

Bolt size is the diameter of the bolt over the thread......... Not the across flats (AF) dimension of the head.

A bolt that has a head 7/16" AF is a 1/4" bolt.... (usually)
 
Last edited:
vics said:
Just adding for the benefit of the OP ........

Bolt size is the diameter of the bolt over the thread......... Not the across flats (AF) dimension of the head.

A bolt that has a head 7/16" AF is a 1/4" bolt.... (usually)
Click to expand...

Thank you this clears this up for me a lot!

So to be sure.. and what @racerone is saying the service manaul torque setting refers to the thread size NOT the head size?

Do I have that right?
 
UNC is what they are.-----Would Sweden welcome a poor outboard mechanic refugee with truck loads of parts..----Sounds like folks there need help with older motors / parts.
 
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Great thank you!

I'm sure they would! Is a lovely country to live (I moved there from UK 10 years ago). Quite a lot of Johnson motors out here for some reason.
 
jasondainter said:
Thank you this clears this up for me a lot!

So to be sure.. and what @racerone is saying the service manaul torque setting refers to the thread size NOT the head size?

Do I have that right?
Click to expand...

Yes The torque figures are based on the thread diameter not the head size.

for a 1/4" diameter bolt the torque is 7-9 Nm

The figure of 38-40 Nm which you read is for a 7/16" diameter bolt.

Manuals usually give recommendations separately for bolts where the exact torque is critical which may differ from the standard figures that you can use where it is not critical.
 
Hi All.

Im trying to locate some replacement bolts for this, the original ones seem like a pain to get (mostly from the US so long postage delays and shipping etc to Sweden).

I found these:

https://www.accu.co.uk/en/imperial-full-thread-hexagon-bolts/32512-SEBF-1-4-20-1-A4

Does anyone know the grade of those bolts. I guess they are stainless steel and and A4 standard (which I read seemed to be marine standard).

Those in the link above would appear to be a direct match. Any thoughts otherwise?
 
vics said:
Yes The torque figures are based on the thread diameter not the head size.

for a 1/4" diameter bolt the torque is 7-9 Nm

The figure of 38-40 Nm which you read is for a 7/16" diameter bolt.

Manuals usually give recommendations separately for bolts where the exact torque is critical which may differ from the standard figures that you can use where it is not critical.
Click to expand...

Thanks this makes perfect sense. I had stupidly read the manual thinking that the head size was what it was referring to as opposed to thread size.
 
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