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Worth rebuilding 100k mile engine?

Started by universalhat, June 08, 2014, 06:41:17 PM

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universalhat

Bad news upon bad news...  I've been trying to diagnose an intermittent but steadily more frequent misfire, and finally got a mind to do a compression test.  130 PSI on cylinders 3 and 4, but down to around 90 on 1 and 2, which jumps to a startling 160 once a tablespoon of oil is drizzled into the cylinder.

I know enough to know that this means the rings have worn quite badly, and that replacing them (and every gasket between here and there) will involve quite a bit of work, time, and money.  The bike's just passed 100,000 miles, so my question is this - would I be nuts to consider doing this involved of a repair on an engine that age?
1990 FJ1200

1979 CB750K, but we're not here to talk about that :P

airheadPete

Poo. Do you like to tinker, and have the facilities?
Or just do a top-end job; that might be reasonably quick and give you quite a few more miles.
I'd suggest a call to Randy. It'll depend on your relationship with the bike and the bank account. (popcorn)
'92 FJ1200.    '84 R100CS
'78 GS750E.   '81 R100RS
'76 R90/6       '89 R100GS
'65 R60/2

Capn Ron

Heck I did a full rebuild on mine with just 20,000 miles because:  I like to tinker, it was smoking slightly at startup and the engine needed some paint.  It's not hard to do...it does take up a lot of garage space and a bit of space in your head to manage the project, but the end result is a fresh FJ engine that will give you another 100,000 miles of service!
Cap'n Ron. . .


There are two types of people in the world...Those who put people into categories...and those who don't.

universalhat

This is all much more positive than I'd expected!  Alright, the Hayne's manual is already winging its way here in the mail, so I suppose once that's here, all that's left to do is run off to some parts store and get a new, well, pretty much everything not made of steel. :P

Thanks for the advice!  Gods willing I don't fuck this up.  Massive picture set and probably a lot of questions, to come.
1990 FJ1200

1979 CB750K, but we're not here to talk about that :P

Mark Olson

of course rebuild it... next will be how far to go.

the good ol while I am in there I might as well ........

they make kits for 1340cc .....just a thought. :mail1: :biggrin:
Mark O.
86 fj1200
sac ca.

                           " Get off your ass and Ride"

Pat Conlon

Yep, as Mark said....beware of scope creep.

The basics:
Next size up on the rings, light bore/hone....send your head out and have your valves/seats/guides/seals freshened up, new cam chain, starter chain and call it a day..

You have a '90, correct?  If so then soft shifting forks should not be an issue.

A note for the future: Put your year FJ in your signature line (via the Profile button at the top of this page) so people know can tell what model FJ you're talking about...it saves you from having to remind us....and it saves us from having to go back a look for your earlier posts.

Help us help you...
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

theLeopard

Quote from: Capn Ron on June 08, 2014, 10:56:55 PMsmoking slightly at startup
why would this lead you to rebuild the engine?
novice mechanic here, only way to learn is to ask
1992 FJ1200

Quote from: George"It is What It Is Until It Ain't Anymore"

Arnie

Quote from: theLeopard on June 09, 2014, 05:03:43 PM
Quote from: Capn Ron on June 08, 2014, 10:56:55 PMsmoking slightly at startup
why would this lead you to rebuild the engine?
novice mechanic here, only way to learn is to ask

Because it implys that oil is getting into the combustion chamber and being burnt, at least until the engine warms up and clearances tighten. This could be caused by valve stem guides, piston rings with slight wear, or (most likely) glazed cylinder bores.
Short answer is: because he's anal :-)

Pat Conlon

Because starting out a long (long) trip with a motorcycle that is anything less than in tippy top condition, is a trip you will take with a lingering question in the back of your mind...

Enough shit happens on the road without starting off behind the eight ball.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

Steve_in_Florida

Well, thanks a LOT there, Robert Pirsig!

How're we gonna reach ZEN, if we're not FORCED to do some MOTORCYCLE MAINTENANCE out there on the road?

(Jes' messin' with you, Pat. Don't get the panties in a wad!   :blum1: )

Steve

Quote from: Pat Conlon on June 09, 2014, 10:54:48 PM
Because starting out a long (long) trip with a motorcycle that is anything less than in tippy top condition, is a trip you will take with a lingering question in the back of your mind...

Enough shit happens on the road without starting off behind the eight ball.
`90 FJ-1200
`92 FJ-1200

IBA # 54823

Burns

Perception is its own reality and trust is a big part of enjoying a motorcycle trip (to echo Pat's observation in total agreement)
There's nothing you can do that can't be done.

andyb

Quote from: Pat Conlon on June 09, 2014, 04:28:58 PM

You have a '90, correct?  If so then soft shifting forks should not be an issue.


The shift forks that Randy carries are different from the ones that I found in my 90.  Replace them while you're there.  Heck, a lot of the stuff inside the cases may not need replacing, but you do it anyhow when it's opened up.