Preparing Crankcases

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fleetingcontact
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Preparing Crankcases

Postby fleetingcontact » Fri Apr 27, 2018 8:34 pm

I'm assembling a lowly bog-standard 40+ for daily use on m'boat. I'm even bothering to lap the mating surfaces of the crankcase. Earlier I got a bit of glass from a shop who not only charged nowt but also ground the edges. Nice.

Anyhow, I taped a sheet of 1200 grit wet'n'dry to it and, with a large dose of WD40 gave it a go, albeit a bit gingerly. The results are seemingly good.

I've compared the surfaces with a steel rule - all seems fine.

Just wondered what any of you think about the notion.

Horsley-Anarak
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Re: Preparing Crankcases

Postby Horsley-Anarak » Fri Apr 27, 2018 8:53 pm

fleetingcontact wrote:Just wondered what any of you think about the notion.


Good to have a leak free crankcase, they can get distorted if they get bashed.
I personally use a little smear of Loctite 5990 on the mating surfaces, Seagull did use an orange colour liquid gasket material on the later models.

1200 I would say was way to fine, a Seagull motor is not a Swiss watch, I would have used 240 grit, you want to flatten it not polish it.

Post a picture or 2 of your progress, always interesting.

Sounds like you are heading the correct way for a reliable motor.

H-A

fleetingcontact
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Re: Preparing Crankcases

Postby fleetingcontact » Fri Apr 27, 2018 9:26 pm

240 grit?!! Heavens above...are you sure? I was under the impression most would use grinding paste and was trying to see if I could accomplish the same task maybe a bit faster...I might go as far as 600!

I remember the comment being made that adding a gasket would possibly lower the compression rate so much that it might not work at all, surely going the other way would drastically reduce end-float with bad results...no?

The surfaces seem quite good already, if the outer surfaces of the cases weren't so cacky I'd be tempted to assume that the motor has seen light use so far. But I suppose some tarnish is expected, the code on the case is GFP 646GG8. ('G' for 'German' ?)

Anyhow I'll have another crack at it and yes, actually post some pics because I lately bought a new camera!

Horsley-Anarak
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Re: Preparing Crankcases

Postby Horsley-Anarak » Fri Apr 27, 2018 9:46 pm

"240 grit?!! Heavens above...are you sure?" Yes I am, you do not need to polish it, just make it as flat as you can, some grinding paste is 120 Grit, what grade of grinding paste were you thinking of ?

"I remember the comment being made that adding a gasket would possibly lower the compression rate so much that it might not work at all, surely going the other way would drastically reduce end-float with bad results...no?" Silicon gasket material squashes down to almost zero,not sure how it may reduce compression rate, or even crankcase volume, crank endfloat would be "increased" if a thick gasket was used, but simply flattening the crancase halves would not affect the endfloat of the crankcase as very little material is being removed, and Seagulls have a massive amount of endfloat.

Each to their own I suppose.
Last edited by Horsley-Anarak on Fri Apr 27, 2018 9:53 pm, edited 1 time in total.

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seagull101
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Re: Preparing Crankcases

Postby seagull101 » Fri Apr 27, 2018 9:47 pm

G means it should have a bing carb.

fleetingcontact
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Re: Preparing Crankcases

Postby fleetingcontact » Fri Apr 27, 2018 10:26 pm

H-A.

what I meant was, if too much material is removed, might this not have a negative effect but the answer is an emphatic 'no' from you - I value your opinion. I confess I didn't know grinding paste came in different grades.

I agree a bit of sealant of some type between the faces is no bad thing, but also recall that some merely go for a smear of oil. Anyhow, any particular brand of sealant? I have a horror of silicon anywhere on the boat since it degrades in a salt-water environment. But I suspect silicon may not be affected in the same way in this application (no air, very flat surfaces under compression, no salt ingress).

Jacob, Bing carbs are German-made hence G as a prefix...no?

Horsley-Anarak
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Re: Preparing Crankcases

Postby Horsley-Anarak » Fri Apr 27, 2018 10:44 pm

fleetingcontact wrote: Anyhow, any particular brand of sealant?


As I mentioned earlier http://www.loctite.co.uk/loctite-4087.h ... 2653339649

Seagull did use an orange type silicon sealant on the later motors, most modern cars use liquid silicon gaskets in a lot of different situations, the Loctite 5990 is good up to 350c and is oil resistant. I use it because it is good, easy to use, readily available and not expensive.

Was your crankcase leaking before you started lapping the mating surfaces of the crankcase?

fleetingcontact
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Re: Preparing Crankcases

Postby fleetingcontact » Fri Apr 27, 2018 10:59 pm

No idea, it came as non-runner and I'm trying to eliminate reasons why it won't start before I try to...just being a bit pedantic to be honest. Can't have the thing let me down when I need it (or disgrace my transom) :shock:

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Re: Preparing Crankcases

Postby Collector Inspector » Sat Apr 28, 2018 2:41 am

Just took a leaflet out of the letterbox, saying that there's no reason I can't have good sex at 65.

Brilliant - because I live at no. 49 so it's not far to walk home afterwards!


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