Can someone please check my math and tell me I'm just overthinking it.

[Mekanix]

Hi,

96 GSX 800

WSM platinum kit, 0.050 overbore.


Rebuilding the top end and I'm thinking the engine shop overbored but I can't say for sure.

The kit was for a 0.050 overbore. That makes the cylinder 3.248'

Boring to WSM instructions of 0.0045-0.0050" makes it 3.2525 - 3.2530"

I can measure with a caliper at the top and bottom and I get 3.253. I don't have anything else to measure with :facepalm:

The piston measures 3.248. Exactly 82.5mm @ half inch up form the the bottom of the skirt.




Here's my dilemma:

I can fit a 4 or 5 or 6 thou feeler gauge between the piston and bore but not a 7 thou.

But by measurements of the piston and the bore there is exactly 5 thou in the difference.


Another thing, When I check the ring end gap it says specifically that it should be between 0.010-0.018 from WSM and 0.010-0.020" in the service manual with a max of 0.039"

Well the way it is now I measure 0.025"


Doing the math. If I were to measure the bore and figure out the circumference I get 10.2196

IF I were to add 0.001" to the bore size and figure out the circumference I get an extra 0.00314" in ring end gap that makes a circumference of 10.2227"

SOooo if I have a 0.025 gap now and I take 0.001 away from the bore diameter that reduces the gap to 0.02186 which is closer to the 0.010-0.020 that it should be according to the instructions I have.

So whats wrong here ?

The ring end gap is bigger than the spec from WSM and the service manual. But less than the service manual service limit.


Is the bore too big?
Is it my measurements that are off?

Am I just over-thinking it?

OR is there absolutely no one that reads the service manual or instructions anymore ?


Thanks for looking

Sorry for the headache

 

[CReynoldsMIZ]

When I got my top end kit, the pistons and cylinders were bored to match from Full Bore. The rings were still new in the package. I just threw it all together, and got 150 psi. I would say your overthinking it, but im not as much as an advanced mechanic as most! Lol

 

[Mekanix]

I'm sure It will work, But its all in the details how long it will work

 

[Dr Honda]

OK.... too many numbers, and not enough coffee yet. (lol)



Here's the deal.....


If you are using an aftermarket piston... stop looking the in the book for specs. Different pistons, and materials will expand at different rates. So... use WSM's specs.


DO NOT try to use a feeler gauge to measure a piston. Pistons are generally not round. They are squeezed to make the skirts tighter. Also... since they are soft... you can gouge something. Use a proper size micrometer, (or good, long jaw caliper) and a bore gauge. Then... just cut the cyl to the spec that the piston manufacture says to use.


Once the Cyl is cut... put a ring in there... and measure the end gap. File it if it need to be bigger. If it's too big, then call WSM, and tell them you need different rings.

 

[Mekanix]

OK.... too many numbers, and not enough coffee yet. (lol)



Here's the deal.....


If you are using an aftermarket piston... stop looking the in the book for specs. Different pistons, and materials will expand at different rates. So... use WSM's specs.


DO NOT try to use a feeler gauge to measure a piston. Pistons are generally not round. They are squeezed to make the skirts tighter. Also... since they are soft... you can gouge something. Use a proper size micrometer, (or good, long jaw caliper) and a bore gauge. Then... just cut the cyl to the spec that the piston manufacture says to use.


Once the Cyl is cut... put a ring in there... and measure the end gap. File it if it need to be bigger. If it's too big, then call WSM, and tell them you need different rings.

Lol thanks Doc, it was late and I tried to get it all out of my head before I forgot

The cylinders were just bored. The shop had the WSM instructions with the pistons and cylinders.

I was mainly concerned with the size of the ring gap since its all that I can measure accurately.
If its supposed to be within 10-18 thou in the WSM instructions and its actually 25 thou measured, that indicates to me that the bore size is outside of the specs in their instructions. It only takes 1-1.5 thou overbore to go from in spec to out of spec.

That's why I'm thinking the shop bored the cylinders too big by 1-1.5 thou.



Will it even matter?

I mean having a ring gap 7 thou above the wsm Spec ?

 

[Dr Honda]

Just so I know... how did you measure the end gap?


To properly measure the cyl... you need a snap gauge, or bore gauge. But, if you think there is an issue... then it needs checked.

 

[Mekanix]

I checked with my feeler gauge set. I just went through each lamination until I found one that fit. It was the 0.025"

Pushed the ring down 1.5 " from the top using the piston and checked each ring one at a time. Both had the same gap.

The math and the gap measurements are telling me its outside the spec given by the MFR.

What I don't know is if it will matter.

I'm all for doing things by the book, the way it was meant be by the people that designed the thing but in reality I don't have the experience to say what the end result will be in this case.

 

[Dr Honda]

Well... the rings will close up, as the engine gets warm. They are normally molly impreg iron, and they grow. (more than people realize) So... yes... they will work, but when cold, it could make it harder to start. But then again... it's only 7 thou big. (and that's not a huge number) OR... the spec listed was for a stock bore, and as the OD changes... so does the gap.

But if they are out of spec... then contact WSM, and tell them to send you a new set. If they are wrong... they need to fix it.