Big twin service bulletin

[trex014]

I think I remember hearing about a service bulletin for the 25hp big twins, something regarding the cooling and putting a pinhole in the water tube to cool something.

Anybody have this bulletin or the bulletin number?

Thanks,
RJ

• This topic was modified 3 years, 1 month ago by trex014.

[JOHN HOLBIK]

I remember a service bulletin from the sixties regarding drilling holes for cooling on the 40hp.I will not have accses to my bulletins until spring.

[bobw]

Here is a previous thread regarding drilling holes in the Big Twin motors:

https://www.aomci.org/forums/topic/rde-18-powerhead-to-exhaust-plate-gaskets/

Bob

1937 Champion D2C Deluxe Lite Twin
1954 Johnson CD-11
1957 Evinrude Fastwin 18
1958 Johnson QD-19
1958 Johnson FD-12
1959 Johnson QD-20

“Every 20 minute job is only a broken bolt away from a 3-day project.”
"Every time you remove a broken or seized bolt an angel gets his wings."

[trex014]

Bob, I’m familiar with that thread and checked it over again but I’m looking for info about drilling a hole in the copper water tube itself, I think I remember it being a 1/16″ hole but I’m not sure where it is supposed to be on the tube and what it’s supposed to cool. I’m 99% sure it was for the mid-late 50’s big twins but maybe I am thinking of the 40hp bulletin.

[fleetwin]

We have had a similar discussion regarding 15/18hps that seemed to have hot exhaust housings. We found that there was a relief hole from the lower cylinder cooling jacket that sprays into the exhaust housing. Oftentimes these cooling relief passages get plugged up with carbon. I’m wondering if your Bigtwin has a similar relief hole…Wish I had a crankcase around to check, but do not… I would prefer having the relief hole coming from the block, then reducing cooling water pressure by drilling into the inlet cooling tube. I will try to find a picture of this relief hole on the smaller engines and post it for you…………Don

[Author]

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