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GS1000 bigbore tolerances?

  • Thread starter Thread starter cockneyrick
  • Start date Start date
C

cockneyrick

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I have been offered a set of 73mm bore barrels & Yoshi pistons etc.

Now the guy has supplied the following info on barrel wear. Can anyone enlighten me whether these barrels are useable or am i wasting my money?


Cyl1 Cyl2 Cyl3 Cyl4
Top 73.03 73,01 73,01 73.05

Mid 73,04 73.02 73.02 73.07

Btm 73.02 72.99 72.99 73.05

Btm measurement is right on the skirt
 
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There shouldn't be any wear at the Btm, or at least very little, so I'd say the cylinders are not worn very much beyond where they were bored oversize. Maybe a couple of the pistons are bigger than the others and the machine shop bored #4 and #1 a bit larger to match the pistons?

What is the cylinder to piston clearance? Hopefully the pistons are marked so you know which hole they came out of.

Assuming the bores on the #1 & #4 are larger on purpose, I'd guess you have some life in those parts. If #4 is just plain worn, then I'd judge the wear as fairly significant, but the parts should still have some life in them, but lesser.
 
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TBH i don't know. Only seen pics of em & this info was passed on.
They are 80 odd mile away & just wondering whether they were worth the cash asked & the drive over to get em?

Basically my heads off with Roger Upperton, who remarked they looked ok but will replace VS seals & tidy it up. Main issue was low comp on N02 cyl, so mebbe the rings were the issue.
In which case a bigbore seemed a better option???
 
What is the condition of the stock cylinder and pistons? If they measure within the service limit then you can reuse them - bottle brush hone the cylinders and install new rings. How many miles on these parts? Suzuki used good material on the liners so your cylinders are most likely fine unless the engine has big mileage.
 
Nessism said:
What is the condition of the stock cylinder and pistons? If they measure within the service limit then you can reuse them - bottle brush hone the cylinders and install new rings. How many miles on these parts? Suzuki used good material on the liners so your cylinders are most likely fine unless the engine has big mileage.
Click to expand...

Engine was a swapper with a friend, who now claims no knowledge of mileage or history.

Bores look good with hone marks still visible. No heat marks on pistons either.

My comp figures were:

No1= 145psi
No2= 87psi
No3= 130psi
No4= 174psi

twas suggested that mebbe the rings had lined up & comp was being lost that way?
Now i'm on a very tight budget so options were re-use my bits with new rings, or buy this Yoshi kit, or a brand new unsellable 1100 kit with slight scoring to crown of one piston?
Dunno how well the name R Upperton translates to Ur side of the pond, but over here he's regarded as one of the best in this area!
 
Low compression on #2 is usually traced to fuel leakage down the petcock vacuum line and into the cylinder. The rings varnish in place and the cylinder gets glazed over. Most likely that's what happened on your bike. Based on your compression numbers the pistons and cylinder are most likely fine. I'd take a good look at #2 and assuming no major wear, I'd slam in new rings (after a bottle brush hone) and go. You could even reuse some of your rings if the budget is tight.

Before you go forward please understand that most aftermarket gasket kits for GS bikes are crap. Purchase OEM gaskets to be safe. In particular, Athena base gaskets are very poor quality - the green colored gasket material is too soft for the application. Be smart and don't pinch penny's on gaskets.
 
Cheers for that Info, especially the Vac line tip, never heard that one before!

And the tap was off a GSX750 to clear the CV carb tops so quite possibly could need a rebuild kit?

Basically here's the options price wise, rebuild using existing parts & new rings with head sorted ?200 ish.
Yoshi kit & barrels alone ?120 (To me pistons & buttons alone are worth that price?)
1100 Bigbore price to be discussed on top of Asssembly.

Decisions decisions :confused:
 
cockneyrick said:
Cheers for that Info, especially the Vac line tip, never heard that one before!

And the tap was off a GSX750 to clear the CV carb tops so quite possibly could need a rebuild kit?

Basically here's the options price wise, rebuild using existing parts & new rings with head sorted ?200 ish.
Yoshi kit & barrels alone ?120 (To me pistons & buttons alone are worth that price?)
1100 Bigbore price to be discussed on top of Asssembly.

Decisions decisions :confused:
Click to expand...

Since the problem is most likely rings in the #2 cylinder, pull the barrels and see if either stuck rings or glazing is your problem. It's probably a simple fix to the motor you have now.
 
Rings didn't appear to be stuck but tbh i really didn't take enough notice.
Pistons etc are stripped & cleaned ready for re-assemble.
How can i tell about glazing?
 
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