Front Head leaking compression

Head Gasket

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michigander52
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Front Head leaking compression

#1

Post by michigander52 »

I'm going to put my Pan project on hold due to an interesting problem on the Frankenstein Knuckle that turned up yesterday. This engine only has 150 miles on it from a top end rebuild last winter.
After a 5 mile ride down the road yesterday I noticed that it was making a strange noise from the front cylinder and thought maybe a pushrod needed attention. After removing the plugs the front one looked lean and rear was sooty. I did a compression test and the front cylinder barely had any. I pressured the cylinder and bingo the head was hissing.
I'm pulling the heads today and wondering what things I should be looking for that may have caused the new gasket to fail
Steve...
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Re: Front Head leaking compression

#2

Post by michigander52 »

Okay, I pulled both the heads and the front head gasket was blown out at the exhaust area and the rear gasket was still holding however did show signs of of heat at the same area. I'm not sure what name brand the gaskets were but they came in a rebuild kit from an independent parts dealer in the local area who dealt in V Twin parts. These are the blue asbestos type with no fire ring or other metal parts.
None of the bolts were loose and the gasket was not miss aligned or scuffed during the original installation. So I have no idea what may have caused the failure. So I guess I'll order some new gaskets of a different style and try again.
Any recommendations on which brand I should look into?
First picture is Rear head and bad spot on gasket.
Second picture is Front head with gasket in place.
Third picture is Front head with gasket removed.
Steve..
Attachments
R Head and Gasket Circled Resized.jpg
R Head and Gasket Circled Resized.jpg (148.83 KiB) Viewed 359 times
F Head W Gasket Resized.jpg
F Head W Gasket Resized.jpg (222 KiB) Viewed 359 times
F Head and Gasket Resized.jpg
F Head and Gasket Resized.jpg (261.61 KiB) Viewed 359 times
panhead_kicker
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Re: Front Head leaking compression

#3

Post by panhead_kicker »

area above the exhaust ports sunk in?
Dont know how likely that is on a knuckle, but whats left?
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Re: Front Head leaking compression

#4

Post by Andygears »

I know little about Knuckles but that seems like a poorly made gasket, the diameter is big causing an area inboard that can fill with carbon. The bolt holes are punched excessively big. The impression shows the outside diameter big also.

I have had good luck on pans and shovels with thin copper gaskets sprayed with aluminum paint and assembled wet.

Andygears
flat38
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Re: Front Head leaking compression

#5

Post by flat38 »

I had exactly the same thing happen on my flathead when I tried those blue gaskets. In over 40 years of running flatheads that was the only time I tried them and the only time I blew a gasket. I have had excellent results with the copper gaskets. I spray them with CopperKote. I have also used gold and silver spray paint and that works, too.

An old Chevy mechanic told me a trick when I was a teenager that has served me well over the years. Small block Chevy head gaskets are steel shim with a coating sprayed on them. He told me to clean and de oil the block and head surfaces with alcohol, lacquer thinner or brake clean and to avoid touching either surface or the gasket faces as the oil from fingerprints could cause a leak. I do that religiously and have only blown one head gasket: the blue one.
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Re: Front Head leaking compression

#6

Post by RooDog »

I toss any blue gaskets that come in a kit. I just don't like them. Period. End of story.....
Copper head gaskets come from $&$ with their Shovel heads, and are historically what have been used on Kuckles since the last century.
Does Cometic make a MLS, Multi layer Steel gasket for Knucks?

....RooDog....
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Re: Front Head leaking compression

#7

Post by panhead_kicker »

Both gaskets failing over the exhaust ports, and its the gasket's fault?
Nah...
Humor me and lay a straightedge across the heads there.
RooDog
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Re: Front Head leaking compression

#8

Post by RooDog »

Helicoils in the head bolt holes.
Perhaps the replacement bolts are too long, bottoming out, and not clamping the head sufficiently.....
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Re: Front Head leaking compression

#9

Post by Buddhahoodvatoloco »

Radical, start with all your surfaces, often overlooked, then do as Roo Perro suggest and check your bolts. :lol:
bobphd
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Re: Front Head leaking compression

#10

Post by bobphd »

RooDog wrote: Fri Jul 29, 2022 5:22 am Helicoils in the head bolt holes.
Perhaps the replacement bolts are too long, bottoming out, and not clamping the head sufficiently.....
If you have earlier 4 fin cylinders and later 40-47 head bolts or helicoiled for 7/16-20 that is probably what caused this. Speaking from experience a long time ago. And I too used to have occasional problems with the blue head gaskets on 74 motors and only use copper for the past 20 years without ever a problem.
Bob
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Re: Front Head leaking compression

#11

Post by michigander52 »

bobphd wrote: Sun Jul 31, 2022 1:31 am
RooDog wrote: Fri Jul 29, 2022 5:22 am Helicoils in the head bolt holes.
Perhaps the replacement bolts are too long, bottoming out, and not clamping the head sufficiently.....
If you have earlier 4 fin cylinders and later 40-47 head bolts or helicoiled for 7/16-20 that is probably what caused this. Speaking from experience a long time ago. And I too used to have occasional problems with the blue head gaskets on 74 motors and only use copper for the past 20 years without ever a problem.
Bob
RooDog, I checked the bolts and they are the proper length and thread completely into the head so I've ruled out that issue.

Bob, these cylinders are new 5 fins and the Heli-coils are the correct 16 tpi with new colony bolts.
After cleaning up the gasket surfaces and checking with a straight edge they are flat so I'm laying blame on myself not tightening the bolts properly ( not torquing tight enough) and the inferior blue gaskets.
I'm going to order copper gaskets and be sure to tighten properly and believe all will be well.
Steve
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Re: Front Head leaking compression

#12

Post by michigander52 »

Not S&S but James has these on their site?
It looks like the S&S gaskets are for 3 5/8" cylinders.
https://www.jamesgaskets.com/products/j ... ead-copper
V-Twin has a set also that resemble the James gaskets for roughly the same price and James website states that theirs are made in USA?
https://vtwin.parts/supplier/v-twin/cla ... et-15-0924
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