Wiseco high comp piston questions. 1981 GS850G.

[Colt45]

I plan on doing cams this fall. 600 bucks for cams plus springs are a little to much for my budget right now. I just want to put upgraded springs in now so I can throw throw the cams in and go. And not have to mess around when I want to put them in. I found a set of 500. Ape springs on eBay for 750 850 and 1000 for 80 bucks but do I need new retainers and clips? And will the valve be strong enough to withstand a 500 spring pressure?

 

[Rijko]

SVS Power sports is VERY quick to respond,
the GS1000 ad is for one piston only :chargrined:

 

[TeamDar]

I was just able to order it https://www.amazon.com/Wiseco-Suz-G...8&qid=1494623479&sr=1-4&keywords=gs750+wiseco

even shipped to canada!

I hope it works for you....that link looks like the part number for one piston/rings/wrist pin. K844 is the part number for the whole big bore kit.

 

[Guest]

I hope it works for you....that link looks like the part number for one piston/rings/wrist pin. K844 is the part number for the whole big bore kit.

Ya good point, I contacted the seller telling them to cancel the order if it's only one piston.

 

[Colt45]

New problem now guys. got it all together with new pistons and valve springs, nut now I think im gonna neew to upgrade the starter. and suggestions? do they make performance starters? and where can I get one?

 

[Chuck78]

I would think that you have a weak battery and possibly a starter that is on its way out. There is a problem that some of the bigger bikes experience with the starter clutch, which is remedied by an electrical modification to be able to crank the starter before switching the ignition kill switch is on. Is this what you were experiencing? The symptom of that would be that the engine tries to fire before the starter has it up to cranking speed, and it makes a loud thud or whacking sound, as I believe the engine is kicking backwards if I recall.

Slight chance you could have your cam timing wrong, which could possibly generate substantially more compression than what you are supposed to have (as well as other side effects with running characteristics and powerband shifting to other areas) and also put you very near piston to valve collision distance

 

[Chuck78]

You might want to just try upgrading a battery if you are cranking, but just not strongly. I would NOT recommend a Shorai lithium iron phosphate battery, however! If you are going something other than a standard high end upgrade high capacity AGM or gel cell lead acid battery (DO NOT buy a standard vented lead acid battery - buy AGM or gel cell if sticking with lead acid), i.e. lithium, I would upgrade your regulator rectifier to a Polaris #4012941 (Shindengen SH775) so that you could then run a lithium battery, and then by the absolute highest capacity lithium battery that you can fit in your GS battery box, and I would highly recommend Antigravity Batteries if you are going with lithium iron phosphate cells (LiFePO4). You cannot charge these on a regular charger, and you cannot let the voltage drop below 9 volts, but they are bulletproof compared to the others on the market and ultralight. Also, your regulator rectifier and charging system needs to be in Tip-Top shape and not vintage design, must be a modern unit and good stator. They are ultralight but also ultra expensive! I am running an Antigravity 4-cell high-powered battery since I do not use it for a starter motor, Kickstart only. It weighs less than 1 lb and is the size of a deck of cards! You would want the big capacity 8 cell or 12 cell version, the biggest that would fit in your battery box, if you are not having other issues as I outlined above, this would be the solution.

 

[Colt45]

After jumping it with jump box and letting it run last night it has no more cranking issue. But I do have a high idle issue. I did tear tear it all down, installed the new pistons, lapped the valves and put in new valve springs. Fired it up and touched the throttle and the idle sticks at 3500-5000. I figured okay I bumped the idle screw or pinched the throttle cable, throttle cable is good and free. I turn the idle screw down and it stalls, turn it back up and it sky rockets after you hit the throttle. I tried carb clean/ starting fluid, and water to find a vacuum leak and nothing changed. Could I have the intake cam off a tooth causing this? It took me close to two hours trying to get it right or what I think it right. I used my clymer repair manual for a guide but it doesn't say anything other than lining the exhaust cam /mark one pointing 1-2mm below where the valve cover gasket goes then to have mark two on the exhaust and mark three on the intake cam 20 link pins apart with it being at top dead center. Scares me that I might be off a tooth.

 

[exdirtbiker]

Please don't look for vacuum leaks with water.... if you find a big leak, you may bend / break stuff you thought was unbreakable.

 

[Drybear]

Hi,
I'm curious about how this modification worked out in the end?
I also plan for wiseco pistons in a 850 cylinder and wonder if there will be any improvement?

Regards,

 

[Chuck78]

You will get a higher compression ratio and have deep valve reliefs that will accept large lift high performance camshafts. The added compression ratio alone will give you a bit of a boost in power, but nothing astronomical, but a good step in the right direction. The ability to run the more performance-oriented aftermarket web or megacycle camshafts using stiffer valve springs will give you a huge boost. Having the cylinder head ported and having a Serdi valve job done to it will also give you some massive gains. Rapid ray on the forums is a pro at this work, check with him.

 

[Chuck78]

Also, getting some custom pistons made is not that difficult. Wiseco would probably design one for you based on the 69 mm K844 piston, but you would have to buy 12 minimum order, and the price would go down from there per piston if you got several other buyers. I have 1-3/4 sets of 920cc GS850 pistons, but they are not for sale. They are from the 1980s. That was a killer street engine (chain drive gs750 with 850 cylinders), a bit unruly with me at the helm. Unfortunately I blew up 1 cylinder. Ray bored out another cylinder for another set of pistons, and I need to get my ported cylinder head back from him also! And my crankshaft back from Pearson racing. This will be the best 750 of all, Yoshimura cams, ported head, 850 cylinders, 920cc pstons.

 

[Drybear]

Thanks for the information.
The K844 pistons and webcams grind #110 are on the way, and I have also got a mild porting of the head.
Open exhaust and inlet system as well..
Anyone who has a similar setup and can estimate the Power gain?

 

[Chuck78]

Big power gains by the seat of the pants feel of it!

I'm not sure exactly how the Wiseco Pistons will fit into a used stock 850 cylinder, however. You need to check the piston to wall clearance and make sure it is within spec especially according to Wiseco, because that piston will expand and contract differently than the stock cast piston. Also, setting your ring end gaps properly according to Wiseco specification is extremely critical. This can make-or-break your engine literally, and also can be responsible for a lot of oil consumption if not done properly. Or breaking the rings if too tight!

 

[Drybear]

Big power gains by the seat of the pants feel of it!

I'm not sure exactly how the Wiseco Pistons will fit into a used stock 850 cylinder, however. You need to check the piston to wall clearance and make sure it is within spec especially according to Wiseco, because that piston will expand and contract differently than the stock cast piston. Also, setting your ring end gaps properly according to Wiseco specification is extremely critical. This can make-or-break your engine literally, and also can be responsible for a lot of oil consumption if not done properly. Or breaking the rings if too tight!

Thanks for your advice.
The cylinderblock is in good condition but I will take it to a workshop for a proper hone job anyway as soon as the pistons arrive.
The bore is 69.02mm and I hope that will be acceptable?

 

[exdirtbiker]

Double check the valve lash spec with those Web 118s.
I think I just realized why my Beast never ran as good as it should... I found on Web cams own web page that #118 cams should have .006" clearance.

Yes, .006". I thought "gee, that's a lot, but they're the mfr"... In a FREAKIN VOLKSWAGEN !!! ?? F'n A !!! They make 2 cams with same name, and I found the spec sheet for the wrong one !!!

Now I gotta go call the guy that bought my bike... I still don't know what the gap should be. I just know I got it wrong.

 

[Drybear]

Double check the valve lash spec with those Web 118s.
I think I just realized why my Beast never ran as good as it should... I found on Web cams own web page that #118 cams should have .006" clearance.

Yes, .006". I thought "gee, that's a lot, but they're the mfr"... In a FREAKIN VOLKSWAGEN !!! ?? F'n A !!! They make 2 cams with same name, and I found the spec sheet for the wrong one !!!

Now I gotta go call the guy that bought my bike... I still don't know what the gap should be. I just know I got it wrong.

Thats interesting.. My cams are the #110 grind and the valve lash spec. is 0.006 and 0.008" Its a lot compared to OEM for these engines, anyone who can explain why?

 

[exdirtbiker]

I could not find where they specify lash anywhere on their website, except for the above mentioned VW cams.
Did they send documentation that says .006" ?? I'm even more confused now!!
I would call them ... web site says they will not answer tech questions via email, you must call.
951.369.5144 Phone (8 am to 4:30 pm California time)

 

[Drybear]

I could not find where they specify lash anywhere on their website, except for the above mentioned VW cams.
Did they send documentation that says .006" ?? I'm even more confused now!!
I would call them ... web site says they will not answer tech questions via email, you must call.
951.369.5144 Phone (8 am to 4:30 pm California time)

If you click on the "grind" number on their website you will find a timing card with the valve lash.

 

[exdirtbiker]

Thank you ! I actually called them today, I was told .006" intake. .008" exhaust.