Fix or Not to Fix that is the quesiton

So I don't have enough time to do a inspection of the #1 cylinder though I was able to redo the compression test. I got #1=90 #2=120 #3=120 #4=120 and #2,3&4 all climbed at exactly the same rate.

I think it is very weird that the compression is so much lower in all the cylinders this time when compaired to the last time I tested. The only difference is that I was running the bike for about 30 minutes before the test at slow speeds so it was probably about as hot as you would want it to get. Where as before I had just taken the bike for a 5 minute run at speed.

So I am wondering if the lower value for the retest means anything and if the cylinders are low enough that I should probably think about doing something like rehoning the cylinder walls before installing new piston rings?

 

Stand Operating Procedure.

If you are going to Pull the Head and Block to do a Ring Job ... you Hone the Cylinders.
Maybe not very much at all.
A few passes to DE-GLAZE the Cylinder and establish a new CROSS-HATCH.

While the Head is off for the Ring Job. Perform maintenance on the Head.
While its removed is the perfect time to De-carbon (De-coke) the Head.
Clean-off the Valve Stems and Faces
Pop on some New Valve Seals
Lap the Valve Faces and Seats to re-establish a new Gas-Tight Seal.

Remove ALL the Exhaust and Intake Fasteners
Replace with High-Quality Hardened Fasteners.
Anti-seize compound where needed.

 

So I've gone through and did a tore the engine down over the weekend to do was wear measurements on the pistons and piston rings to look for the cause of the poor compression.

It turns out that the cylinders in my engine are 2nd oversized and yet there were 3 piston rings on there which matched the spec for the regular 65mm piston. The piston that had the bad compression had 2 small rings and the #4 had one (and yet had good compression). So I guess I'm going to have to order a new set of rings for the engine. Even the 'good' rings were worn past the recommened spec.

So my plan now is to order up some new piston rings for the engine, some seals for the carbs and a couple sets of new fasteners. So hopefully after the next reworking I'll be able to get the engine is proper shape (it just blows my mind that the engine ran as well as it did with three piston rings with ~2mm end gap!).

 

I don't think you should pour any money into rehabilitating that Engine block.
If you are absolutely intent on "Building" an Engine for your self ... Start-off with a GOOD FOUNDATION!

Find an Engine Block that is still STANDARD.
Beak the Glaze or Lightly Hone the Replacement.
KEEP your NEED for Special Rings and Pistons: Minimal.

A good used Block, Honed or De-glazed with NEW Rings will put you in a stronger position for Building the Engine ... and Leave You With SOMEPLACE to go ... if there is any problem with the Piston Rings!

 

I don't know if this changes much but the pistons were 2nd over sized also.

I am interested to hear what you guys think about what I should do though. So this is where I stand right now:

The current engine set up has 3 small piston rings in it but I swapped a bad one from the #1 cylinder and put it on the #2 cylinder so that no piston would have two bad rings.

Therefore #1 is one bad and one good, just like #2 and #4. #3 has two good ones (the good ones have an end gap of 0.4mm which is over the spec).

I took the bike for a quick run today and it idled much much better, it started out at 4k with the previous setting and then came down nicely once I reset the idle adjustment screw. And unlike before the engine will idle on its own without stalling.

I still have to ride it some more to fully test it out but it actually doesn't seem to bad off right now.

I was thinking that since the 2nd OS pistons are within spec to the 2nd OS cylinders I could just get a new set of rings. However I also have a set of standard sized cylinders that I could get honed out if you guys think that would be the best idea.

Anyway I would really like to hear what you guys think I need to do to the engine to get it to the point where I can confidently take it on a ~2000km trip without doing excessive damage to the bike.

PS Hopefully I'll be able to do a compression test on the bike tomorrow. And I would be very interested to hear if anyone thinks that even though the piston ring configuration is a little weird, if I get good compression the engine is actually ok.

 

bump-a-dee bump bump
bump-a-dee bump bump

 

I hope you haven't exchanged the second ring with the first ring, since they are different shapes. (and have a upside and downside too :wink: )

Well, since all pistons are second oversize already, this is what I would do.

IF the cilinderblock is within spec for the second oversize and not warped, I would let it hone lightly so there is a nice new fresh crosshatch. (For letting the new rings break in.) I would buy 4 sets of new 2nd oversize piston rings (and oilscraper rings). Clean the pistonring grooves and pistons carefully, decoke the head (as suggested before), replace the valve seals, adjust the valves since the head is off the engine anyway.

Then break the engine in again and it should be good as new.


grz Thijs