Force120 miss cyl. New development

[Beno]

Working on this engine. re-did the compression test.  here are my numbers

123/150+/150+/150+

What do I do? I re-checked it a few times.  In the past I kind of always thought that anything over 120 has gotta be a good cyl… now I’m re-thinking that.

Is this bad enough to justify that the head is leaking?

Tear down the head?, sand, plane and reattach? gonna be a 4 hour job no matter how I cut it.

I have a leak down tester at my friends house. should I do a leak down test first?

[frankr]

Easiest thing first.  Not familiar with that engine but does it have intake bypass covers on the side of the powerhead If so, remove the one on the low cylinder and take a peek inside for possible damage such as a busted ring.

[Beno]

good idea..  also I’ll get the bore scope going, it’s the top cyl.. so It may be easier. that way.

along with the leak down test at BDC

[Beno]

Ok heres the Lower Reed Set..

[Beno]

Here is the Upper Set…

[Beno]

and yes. the cyl with the low compression happens to match the cyl with the chipped reed.

[Beno]

Ok pulled the head. here’s the inside:

you can see the one black Cyl1.. I’m guessing its black because of unburned oil and carbon and water combining? or just misfiring

it’s REALLY hard to see but here is what looks to be Failed head gasket location.. This doesn’t have a actual broken gasket (hence why compression stayed above 123psi?)

this is a tough debug… but you see how the metal contact part of the head gets shiny and polished.. it’s vibrating there and not firmly Connected to the gasket at that point.. each power and exhaust stroke it’s expanding and contracting.
it will never burn thru because on every stroke it’s getting some fresh cooling water past it..

[Beno]

hard to see.. but the rusty area is telltale

[Beno]

I’m waiting on the arrival of the new head gasket.
does anyone know what the best “scuffing” methodology approach is for the block side of the preparation, I’m using decent sandpaper about 150 grit or so.
should it be scuffed all in one direction?
or circular using the piston center as the basis?
or some sort of random?
or scuffed in arrays.. like spokes of a wagon wheel?
see pics of the block attached.

[crosbyman]

it is called cross-hatching for a reason…

https://youtu.be/f7JuMGsyDAg

 

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[Author]

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