81 GS1100E mods

[Anonymous]

I have a stock 81 GS1100E. I have bought a 1261 block and pistons and a set of Cam Motion G21/G5 cams. I am new to hopping up motorcycles. I have built several drag cars over the years but this is the first bike. I plan to drive it on the street mostly with some drag racing. Where is a good place to find gasklets for this and some info on hoppinf up these bikes. Will my stock carbs work? It has a Mac 4into2 exhaust on it know with that work ok. I am wondering if the cams may be to big for what I want to do. I bought all of this stuff from someone who had it sitting around but it has not been used. Thanks for any help

 

[Anonymous]

Do you realize that a kit of that size can not be installed without having the cases bored out to accomodate the larger sleeves???

 

[Anonymous]

The block came with sleeves already installed. Or does the crank case also need to be bored out?

 

[Anonymous]

I believe that is what i said in the post--Usually you cant go over 3mm oversized without splitting the cased and having the sleeves fit to them. The 3mm gives you about 1166cc

 

[Anonymous]

I did not know that. Like I said this is the first time I have tried to do anything to a bike other regular maintence. I don't feel like getting that much into for now. I would guess that the cams I have are too much for a stock motor without more compression and extra cc.

 

[Anonymous]

I did not know that. Like I said this is the first time I have tried to do anything to a bike other regular maintence. I don't feel like getting that much into for now. I would guess that the cams I have are too much for a stock motor without more compression and extra cc.

Sell the kit and just over bore the barrels to1166cc get higher compression pistons and while you have it apart get a street porting

 

[Anonymous]

Benny,

If your interested in selling that kit let me know. I have my 1100 completely apart (split the cases yesterday) and I'm looking around for new pistons right now on ebay and at parts houses. Just a thought - don't know if you wanna sell - but if you do let me know. Thanks - Steve

 

[rosco15]

check out the forum on dragbike.com. look through the archives. i get my gaskets from cometic.

 

[Anonymous]

The kit is used it came with 2 sets of pistons one set of flat tops and one set of domed pistons. The pistons have rings on them but I wasn't planning on reusing them. It does not have the clips that hold the piston pin on though. How about $325 and I will take care of the shipping as long as it is the US. Email me if you are interested 69-50@excite.com

 

[massakins]

Benny, you might not want to sell that kit just yet. The first thing to do to any GS1100 that will see hard use is ensure the crankshaft is true and has been welded (standard on 1983 GS1100ESs and newer GS1150s). Secondly, it needs the clutch basket reinforced. There are several levels to this.

If the crankshaft is not welded it will need to be removed from the cases (saw one done once in the top half without remivng the top end but don't recommend it); cost is $80-100 for the welding. At this point boring the top case half is simple and only costs $40-50 after removing the cylinder studs. Replace these studs with HD ones ($75), install your 1261cc kit and have fun (BTW, nylon buttons don't come loose like piston pin circlips can and are reusable). Hi lift cams beg for more air flow than the stock carbs and ports support but the extra displacement will make it very powerful at lower RPMs until then. Have fun.

 

[Anonymous]

Indexing and welding the crank and reinforcing the clutch basket are excellent ideas. If do you go that route, I would recommend that you get straight cut gears for the cluth also. (Not sure if your '81 has straights already, my '80 doesn't.)

The angle cut gears are a big reason that those clutches let go in the first place.

 

[massakins]

Several additional items come into play when straight cut gears are being considered. First, realize there are two sets readily available (possibly others custom made or in limited production as well). The two straight cut gear sets are either standard ratio (49t crank and 87t clutch for 1.77/1 ratio) or GS750 ratio (46t crank and 99t clutch for 2.15/1 ratio). Both require the crankshaft to be partially disassembled for the gear installation but allow the crank pin beneath the gear to be welded. Additionally both require the clutch gear to be replaced, but this is almost identical to the work required for building a HD basket with a helical gear anyways, so is a wash.

The GS750 ratio gears can be had very inexpensively but you'll have to work more to get them and must make several other changes to your bike to accomadate them. I've procured several sets for less than $100 but had to remove them from a crankshaft and clutch hub; best to magnaflux them once removed before proceeding further. Once installed you'll have to 1) clearance the cases to make room for the bigger clutch hub gear (some motors only require metal removal, others develop a hole that must then be welded over), 2) replace the oil pump gears with a set from a GS750 to restore your oil pressure (or use the special MRE gears if already using the GS750 gears), 3) regear your final drive to compensate for the changed primary drive (adding one tooth to the countershaft is a close approximation) and finally retune your clutch lockup to regain the same pressures at the now reduced rotational speed.

The stock ratio gears cost more to purchase but don't require other changes to the system. Several years ago they could be had for $275 new. Quite the bargain when you consider items 1) through 4) above.

Overall, a straight cut gear conversion can cost an additional $750 or more over simply welding the crank and reinforcing the stock basket. But your drivetrain reliability problems are over, period.

With a slick (especially a car tire) and a wheelie bar on a 8 second bike that launches with 1.30 second or quicker 60 foot times I say absolutely you should do this. With something less than this you can survive with the helical gears and careful inspection. The farther you slow from this example the less frequent inspections should be. Good luck.

 

[Anonymous]

Thanks for taking the time to supply that information

 

[Anonymous]

I just got a quote from the guys at Cope racing on straight cut gears for my 1100. For indexing and welding the crank, straight cut gears on the crank and clutch hub, and reinforcing the clutch hub - $600.

I'll stick with the standard ratio gears and do any drive line duning at the front and rear sprockets, thus avoiding any machining to get the 750 clutch gear to fit.

Good post - informative.

 

[Anonymous]

I just got a quote from the guys at Cope racing on straight cut gears for my 1100. For indexing and welding the crank, straight cut gears on the crank and clutch hub, and reinforcing the clutch hub - $600.

I'll stick with the standard ratio gears and do any drive line duning at the front and rear sprockets, thus avoiding any machining to get the 750 clutch gear to fit.

Good post - informative.

did the price include magnafluxing and did they mention anything about if any parts did not pass the magnafluxin testing

 

[Anonymous]

Magnafluxing - good point. I didn't ask them, I just assumed they would do it prior to assembly. Magnefluxing is prettty easy to do - I used to do it myself when I worked in a machine shop. It just involves a magnetic field and some fine ferrite powder. I'm not sure what they would charge for it, but I can't imagine it being costly.

The quote that I posted was assuming all components of the crankshaft assembly are usable.

I also got a quote on a competition valve job for $240. That seems very reasonalbe to me, as the local yokals want $300. This was just labor, no guides, seals, or unusable parts replacement.

 

[Anonymous]

Check out the 1100 on ebay.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=1874551962

 

[Anonymous]

Magnafluxing - good point. I didn't ask them, I just assumed they would do it prior to assembly. Magnefluxing is prettty easy to do - I used to do it myself when I worked in a machine shop. It just involves a magnetic field and some fine ferrite powder. I'm not sure what they would charge for it, but I can't imagine it being costly.

The quote that I posted was assuming all components of the crankshaft assembly are usable.

I also got a quote on a competition valve job for $240. That seems very reasonalbe to me, as the local yokals want $300. This was just labor, no guides, seals, or unusable parts replacement.

All i was concerned wit was the possibility of you having t go for a bundle for parts that they condemn. I lost my first clutch basket to falicon that way

 

[massakins]

A few more thoughts about straight cut gears:

1) The reason they are more reliable in high stress applications is because 100% of the energy transmitted from the crankshaft gear is applied to the clutch hub gear in the rotational direction. Helical gears, used by the OEM because they are quieter, transfer most of their force in the rotational direction but also some in the lateral direction. This latter force is what seperates the backing plates from the rivets and generates all of the metal chip supon failure.

2) A measurable power gain is realized with the straight cut gears since there is no energy lost to the lateral motion mentioned above. I think this is in the neighborhood of 1-3% but don't know for sure. Anyone that's realized this gain please comment for the rest of us.

Reliability is the primary reason for this modification, but the extra power is a nice plus as well. Just my thoughts.

 

[Anonymous]

I don't have any firsthand experience - yet - but your analysis of the forces involved was dead on.