Top End Rebuild - What Parts are needed?/What Other Parts should be replaced?

WilliamJ

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Hello,

This past weekend my 1977 XS650D broke down when I was on a ride where I lost power(couldnt go past 30mph in 5th gear) and oil started coming through the left exhaust.
I anticipate this being caused by Piston Rings, Exhaust Valve issues, or a damaged Piston. To determine which and repair the damage I anticipate having to Pull out the engine and rebuild the top end.

When doing this Top End rebuild I was wondering what other parts I should replace?
I am planning on buying a Top End Gasket kit, Piston Rings(once cylinder bore is measured), and valve parts as needed from MikesXS.

Top End Gasket Kit(is there a better/more cost effective one other than this?):
https://www.mikesxs.net/gasket-kit-top-end-yamaha-xs650-1977-1983.html

If it is Rings should I replace any timing/Valve parts?
Is there any bottom end parts I should replace while I have the engine removed?

Are there any Special Tools I should buy right away? I am planning on getting a Bore Gauge, Valve Spring Compressors can be rented from my local Autoparts store.

This will be my first 4 stroke top end rebuild and would appreciate any and all advice/tips you have. I always do my own work on my motorcycles and am not a novice at wrenching, I just have not had a (4 stroke) bike need a top end rebuild in the past.

Thank you!!
 

azman857

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I wonder if it was a holed piston. I'd also think about a front camchain guide while the cylinders are off. Depending on condition of the original, the cam chain tensioner arm. Perhaps do the elephant foot mod to the rockers. Valve relap or total valve job. I'm surely forgetting something....
 

Jan_P

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OK my thoughts
It is quite a lot of job opening the engine it needs to come out off the frame ( Mine 1980 has anyway )
you need to split the Cam chain.
Given the amount of work ... and costs for gaskets ..
It is in my view better to do a bit more and thorough job once in there
Most people would replace cam chain and guide. Inspection can help but those I know would replace for new

I once had a Cam ball bearing with excessive play I cannot say if it is a common problem. But they are moving parts with a limited life span. I would replace those.

Depending on inspection and future plans and so on. Valve springs ..I Think those can be measured against specifications
but don't cost much.
Valve guides needs to be evaluated .. I took my cylinder head to an experienced mechanic who could make an evaluation.
Inserting the valves and feel the play.
Once the Cylinder is off
I would try to make an evaluation of the bottom end . There are specifications about sideways allowed movement
In service manuals that I found on the web.
And the same Experienced mechanic can by inserting the wrist pin .Estimate the wear in the conrod small end.
Changing the Con rods is again a major work. Not sure if it is worth it. Better buy a replacement crank.
But the crank has a solid good reputation.

I would guess that this is an Exhaust valve ... broken.
Im in Europe so I don't know parts availability .But a salvage head could be an alternative.

There are ways for fault finding if the motor is not split yet. I cannot remember them please google.
Checking if the valves are leaking you turn the head upside down and pour gasoline into the heads.
Plugs in. If the level sinks .Need to do something.

Depending on how you do it perhaps a tool for joining cam chain will be needed.
It can be done without. But that depends on skill and if any friend can help.
 

Jim

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First thing first.
I wouldn't order anything until the engine is out and apart. Best to make sure you know for sure what you need before ordering.
1+ on that.
When you do order parts, try and use OEM as much as possible. Partzilla still has a fair selection. Look to Hoos Racing for the cam chain guide and Cruizinimage has pistons and rings that a lot of people here use... including me. There's a top end buildup thread in the Tech section. I've never used it, but I hear it's ok.... :rolleyes:
 

5twins

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Don't buy that gasket kit you linked to, it's a total ripoff. You can get all that stuff of the same or better quality for probably half the cost.
 

stinky78

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Yeh that kit is way over priced for a no name kit, if buying a kit I’d probably get an Athena or Vesrah, last time I looked you could still get all of the gaskets etc from Yamaha, I’d be surprised if the total came to more than that for genuine parts from Partzilla or the like.
 

WilliamJ

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Thanks for all the replies!!!
I got the engine taken apart and it was a hole in the left piston.
The valves and pistons are in terrible shape (see pictures). Do you have any idea how this type of damage is caused?
I just bought this bike a couple weeks ago so I don’t have the full history of it. I have never seen valves/pistons in this bad of shape.
 

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WilliamJ

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Thanks for all the replies!!!
I got the engine taken apart and it was a hole in the left piston.
The valves and pistons are in terrible shape (see pictures). Do you have any idea how this type of damage is caused?
I just bought this bike a couple weeks ago so I don’t have the full history of it. I have never seen valves/pistons in this bad of shape.
 

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Mailman

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A hole burned in the top of a piston can be caused by the timing being off ( too far advanced ) which causes pre ignition or pinging. Other contributors can be running too lean and incorrect spark plugs ( too hot ).

As for the head, I can’t see the too clearly, but it’s not uncommon for them to look all black and carboned up. You’ll have to clean everything up and pull the valves to get a better look, I’m gonna guess you can just lap the valves and check the springs and install new valve guide seals.
 

5twins

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The light gray or whitish coloring on the right cylinder's valve heads and combustion chamber would indicate this thing was running lean and hot. You haven't given much info on the bike - has it been modded (pipes and pods)? If so and the carbs weren't re-jetted for that, maybe that's why. The '77 carb set came stock with very small mains, #122.5's, the smallest put in any 650. They're fine for an all stock machine but are quickly out-paced if you do any modding.
 

Jan_P

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Ok Ok
With a bit of Luck it might not be a very large costly problem .
Cylinder head Pour some gasoline in them ( spark plug in ) se if they are leaking and how much.
Cleaning
Lapping can fix it with luck.
Rocker box to my eyes looks rather clean please inspect surfaces and play.
Inspect the cylinders and preferably measure.
on the top crown of the piston under the soot -- there can be a size stamped in
3 digits.
I Bought a XS 650 SE 1980 ten years ago with stock pipes and filter and stock spark plugs
It had a severe engine knocking at times
I ended up going up two steps on main and one step on the other jet.
Running perfect ..thereafter .but consuming a bit extra fuel Plugs.on the black side.
Less when longer runs at higher speed under warm climate.But still black
Now we can se what can happen if mixture gets to lean. And this is not the first one I have heard off
 
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