AAAGHhh a big bore kit and then discovered it already has genuine 850 pistons :O

[GS750]

AAARGHHHHHH what more can i say...

My bike was getting sick, loads of blow-by and lack of power, so I bought the wiseco 850 kit from the U.S ($150 cheaper than here in OZ), and intended to bore the ole girl out and go with a nice engine mod....

In a really big hurry I took barrels to be machined on Friday late arvo. Then today after work I went and removed the ole PIS5tins and discovered something SHOCKING :O

It has already had genuine Suzuki 850 PIS5tins (69mm) installed :O BUGGER!!!


Now I really dont know what to do..... The Suzuki pistons look good, minimal wear etc... so I am debating which way to go!


Do I just get another 750 set of barrels and bore em out, and bore them to what??
Do I bore it to suit the suzuki pistons and just re-ring them,
or do the bore and install the wiseco kit anyways??

Do I search the minimal parts available here in OZ and hope and pray that I can find some original size 850 barrels to suit a 31yo bike that have minimal wear??

AAAGHhhhh flippin hell, what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do what to do!


WHY CANT PREVIOUS OWNERS TELL YOU THAT THEY HAVE ALREADY DONE A B.B. KIT????

[GS750]

Also forgot to ask what barrels will fit onto it.

Its a GS750B Engine no# GS75024858

[Ghostgs1]

Hi GS750, tkent posted here that he had installed 850 pistons and cylinders on his 750. I think that he said it is a bolt on with no machining. Check with Tom or search for his post. Good luck. Ray

[tkent02]

Hi GS750, tkent posted here that he had installed 850 pistons and cylinders on his 750. I think that he said it is a bolt on with no machining. Check with Tom or search for his post. Good luck. Ray

Go with the kit you bought, at least you get higher compression.
Cylinders from a '79 850 with VM carbs will drop right into your 750 cases.

I have heard cylinders from a '80 or later 850 with CV carbs need to have some grinding done to fit into the 750 cases. Never done it myself.

The year models may be different where you are.

[GS750]

Go with the kit you bought, at least you get higher compression.
Cylinders from a '79 850 with VM carbs will drop right into your 750 cases.

I have heard cylinders from a '80 or later 850 with CV carbs need to have some grinding done to fit into the 750 cases. Never done it myself.

The year models may be different where you are.

Hi peoples, thanks for the reply's. My barrels may or may not be 850's, either way they are actually already worn, thats the reason why I decided to lash out and buy the wiseco 850 kit for what I thought was an original 750........

I bought the wiseco kit because it was suffering some serious blow-by and would use 1ltr oil on a 300Km run (most blowing out over my left boot)

To use these barrels I would have to go to the 850 oversize 70mm pistons since they are pretty severely worn.

Im currently thinking it would be best to just get some more 750 barrels and boring them out to suit the pistons I already have fitted to the bike (the 850 genuine Suzi ones) and fit them with new rings, keep the Wiseco kit for another 5-10 years and then flog it off as a goldmine for what would then be a 40yo bike (hopefully LoL)

[tkent02]

Hi peoples, thanks for the reply's. My barrels may or may not be 850's, either way they are actually already worn, thats the reason why I decided to lash out and buy the wiseco 850 kit for what I thought was an original 750........

I bought the wiseco kit because it was suffering some serious blow-by and would use 1ltr oil on a 300Km run (most blowing out over my left boot)

To use these barrels I would have to go to the 850 oversize 70mm pistons since they are pretty severely worn.

Im currently thinking it would be best to just get some more 750 barrels and boring them out to suit the pistons I already have fitted to the bike (the 850 genuine Suzi ones) and fit them with new rings, keep the Wiseco kit for another 5-10 years and then flog it off as a goldmine for what would then be a 40yo bike (hopefully LoL)

What size is cast on the cylinder, 748cc or 843cc?
What is the diameter of the sleeve?
Does Wiseco make a 70mm oversize?

[GS750]

On my barrels is marked as 748cc.

I measured the barrels tonight and they are 68.91 to 68.94mm

The 850 suzuki pistons that are currently fitted to it are all around 68.4mm.

The suzuki pistons dont seem to be too loose in the barrels and there is minimal wear on them too, so I am now wondering if I should just re-ring them and hone the bores?

I am guessing that when the barrels were machined to the 850's they were done with insufficient clearance which would have resulted in the broken main compression rings on 3 of the 4 pistons.

Is it worth removing the lip at the top of each barrel if I was to just re-use the suzuki 850 pistons or would this increase the compression ratio? The lip seems to be .32mm consistently on all cyls which would mean that the clearances on the pistons were very very tight when they were previously bored.

The barrels are all very shiny, though slight cross hatching can still be seen in all 4 pots.

If they are OK to just hone then I would still keep an eye out for a set of 750 barrels so I can have them machined for the wiseco kit, and store the whole lot for use later on down the track. I figure that since it is already a 31yo bike it would be worth having them as spares, and the kits would only go up in price and probably become difficult to obtain in the next 5-10 years.

I guess its not really such a bad outcome, but its still a shock to know that a previous owner didnt bother to pass on the info about the fact that it was actually 850'd.

I also discovered that there are several leaky valves and Im now wondering if the 850 heads had bigger inlet and exhaust ports or if they are the same as the 750's?

Now another series of questions:

Which headgasket should I use? The original 750 genuine suzuki metal one, the 850 suzi one, or the wiseco?

Which base gasket too because the 750 and 850 ones that I measured (same material) are different thicknesses.

The barrels also didnt have the O'rings installed on the bottom where they go into the engine block.

Are the 850 tensions the same as the 750? (I guess they would be but would like confirmation)

Thanks again for all the helpful advice and suggestions.

[tkent02]

On my barrels is marked as 748cc.

I measured the barrels tonight and they are 68.91 to 68.94mm

The 850 suzuki pistons that are currently fitted to it are all around 68.4mm.

The suzuki pistons dont seem to be too loose in the barrels and there is minimal wear on them too, so I am now wondering if I should just re-ring them and hone the bores?

I am guessing that when the barrels were machined to the 850's they were done with insufficient clearance which would have resulted in the broken main compression rings on 3 of the 4 pistons.

Rings can break from insufficient end gap, over revving, other reasons too.

Is it worth removing the lip at the top of each barrel if I was to just re-use the suzuki 850 pistons or would this increase the compression ratio? The lip seems to be .32mm consistently on all cyls which would mean that the clearances on the pistons were very very tight when they were previously bored.

There are ridge reamers for this, to not ream it could possibly ruin the new rings.

The barrels are all very shiny, though slight cross hatching can still be seen in all 4 pots.

Needs a good hone for sure.

If they are OK to just hone then I would still keep an eye out for a set of 750 barrels so I can have them machined for the wiseco kit, and store the whole lot for use later on down the track. I figure that since it is already a 31yo bike it would be worth having them as spares, and the kits would only go up in price and probably become difficult to obtain in the next 5-10 years.

I guess its not really such a bad outcome, but its still a shock to know that a previous owner didnt bother to pass on the info about the fact that it was actually 850'd.

I also discovered that there are several leaky valves and Im now wondering if the 850 heads had bigger inlet and exhaust ports or if they are the same as the 750's?

850 heads are identical to 750s, same part number. All valves are the same. The only difference is the 850 uses 1000 cams.

Now another series of questions:

Which headgasket should I use? The original 750 genuine suzuki metal one, the 850 suzi one, or the wiseco?

The 850 or the wiseco depending on which pistons you use.

Which base gasket too because the 750 and 850 ones that I measured (same material) are
different thicknesses.
The thinner one will give higher compression.

The barrels also didnt have the O'rings installed on the bottom where they go into the engine block.

use them

Are the 850 tensions the same as the 750? (I guess they would be but would like confirmation)

Thanks again for all the helpful advice and suggestions.

I would not use the new Wiseco pistons on these worn barrels, use the 850 pistons or find a new cylinder and bore it.

I would go with the new barrel and the Wiseco pistons if it were to be my keeper bike, would go the other way if a fix and flip bike.