GS1000S Big Cams, maybe too big?

[terry]

I found a really nice pair of race cams for my GS1000S at a swap meet today, but not having a vernier caliper with me at the time, I was not able to measure them. Anyway, when I brought them home I measured them and compared them to a couple of sets of stock cams I've got kicking around, here's the result:

GS1000E GS1000S "LUMPY" CAMS
IN: 36.2mm 36.8mm 38.4mm
EX: 35.9mm 35.9mm 38.4mm

The "Lumpy" cams are maked 545A which I assume is the lift, as I roughly worked out that the stock lift is around 10-11mm, and that would make these around 12-13mm?

As you can see, there is a big difference between the factory items and my new toys, so my question is, are they too lumpy for street use? Will I have to relieve the inside of my cam cover to make them fit? I'm not sure of the required valve timing set-up, but these cams appear to be regrinds, and the larger lobes follow the exact same profile as the stocker, although there's obviously more duration as well as lift, due to the shape.

The rest of the engine is stock, but it's the later GS1000S 8 valve engine, so has pretty large ports and I have the choice of 34mm CV or 33mm slide carbs, a hand made "Megacycle Engineering" exhaust system, and eventually I'll fit a Wiseco 1100 kit when my flowed head arrives back from the US. (a mate in Boston is doing it for me)

My old Yoshimura cams were about 1mm larger than stock, and the difference in acceleration and top end really was dramatic, so I'm keen to try these out, so any advice will be mucho appreciated! Cheers, Terry. :twisted:

[saaz]

Terry

Factory specs for my 78GS100 are cam lift 8mm in, 7.5 out.

Cam height 36.32 to 36.36 (service limit 36) in, 35.77 to 35.81 (service limit 35.5) out.

The street cams I put in years ago were about the most you would want to do without having to do a lot more expensive valve components. The haed was ported to go with them. The lift for these is 9.8mm in and out, 254 degree duration at 1mm lift. I don't have info on the lobe heights without actually measuring them. The height you have look a bit similar to what mine probably are.

The reground cams have a different cam profile as they do not have the quietening ram of the standard ones. valve clearances are .15 to .20mm, compared with .03 to .o8 standard. From memory the more radical race cams did requite some head relief work plus changes to the shim and bucket arrangement.

[simon lambert]

Terry you are a total bastard.. how do you find this stuff??

To me the amount of lift suggests cam cover relief and shim under bucket
would be required.. I have the same cams in one of my motors..
If you dial them in you can get them to work well for the road..
Mine were great on a road trip from syd to Brisbane.. not so great for
the Xmas toy run in the city though.

My cams were supplied by Phase 4 here in Brisbane about 20 yrs ago..
They have long since closed but the two guys that ran the business are still around..
Ed Cross is one of them and he runs Startline motorcycles.. they don,t have a web site but I can find a phone number if you want..

[terry]

Thanks Guys, well if you think I'm a bastard now Simon then maybe I shouldn't tell you I only paid $80.00 (about $50.00 US) for them both!

I almost fitted them to my bike as I just did an "el cheapo" top end rebuild on my spare "ET" engine so I could ride the bike while rebuilding my "S" engine properly, but as I'd been having problems with it I left it standard.

Considering I just ran my flex hone hone thru the standard original 50,000 mile cylinders, re-used the second hand pistons and rings, and even re-used the head and base gaskets (albit with careful cleaning and torqueing) I was surprised to see a genuine 220 Kmh (137.5 Mph) at around 10,000 RPM in 5th gear with standard gearing yesterday on a nice quiet stretch of road, magic!

The manual cam chain adjuster worked really well too, I was surprised at how quiet the engine now is with only minimal cam chain slack. I spoke to my cousin on Saturday about it, he's an ex-factory Suzy mechanic, and he said he'd fitted quite a few manual adjusters for hi-po GS musclebikes back in the '70's and '80's, as there was a lot riding on what was considered a fairly weak spring. Thanks again guys, I'll keep them safely in a box until my engine is ready to reassemble.

I also found a small "high flow" fuel tap at the swap meet too, the screw spacing is all wrong though, so I'll have to make an adapter, so more on that later. Cheers, Terry. :twisted:

[simon lambert]

The manual cam chain adjuster is a must..
I really struggled with the STD one for a number of years..
Now the manual one is almost a SRD fitment onto my engines..

I really need to know where you find these bits..
Although I have heard of a GSX1100 for $600 that I am considering..

[saaz]

I just found my scribbled down timing specs for my cams (Peter van Muers did the head and cam work). They are 53 - 23, 23 - 53 which is fair bit different from standard. Much like stock to 3000 or so, then it starts to boogie a bit more, then 6000 hits...wish I invested in some smoothbores years ago.

[saaz]

Oh yes, forget to type in a crucial point..timing is measure at 1mm lift.

[ToddB3]

Terry,

Nice buy on the cams! something to keep in mind though, I replaced my stock cams with stage 3 Yoshi racing cams on my 900RR that I bought second hand and noticed the same thing you did about how much larger they are than stock. After talking to a Yoshimura tech I had to buy heavy duty valve springs because if the valves bounce the least bit you will have a catastrophe on your hands...

[terry]

Thanks for that Todd, how do the Fireblade springs compare to, say, the springs in your GS750?

The reason I ask is because my other passion is old Honda CB750's (single cammers) and apart from the 1977-78 F2/F3 models, their springs are absolutely puny in comparison to my stock GS1000 springs?

My 1979 GS1000S had Yoshimura cams as mentioned, and a 1085CC big bore kit when I bought the bike for spares (now in line for a full-on "restification" as soon as I can sell one of my other bikes to raise the funds) and looked like it had been raced mercilessly prior to it's retirement, but surprisingly it was running stock springs with no obvious ill-effects.

I guess my question is, are H/D springs that necessary, considering that the down side of heavier springs is normally accelerated valve train wear? Anyone know? Cheers, Terry. :twisted:

[saaz]

Yes, there is that tradeoff of spring pressure and getting the valves to be where they are supposed to be all the time. At the time I did mine I put in the valve springs that the engine builder said I needed. The redline was also increased safely to 9000rpm.

But these days spring technology has changed a bit, so it may be worth finding out what the modern options are. Newer springs have less trouble with coil bind, can be spiral wound etc etc. But using those two heavy old valves may mean h/d springs. The shim over bucket design is also a lot heavier, so heavier springs may be needed. Going to shim under bucket was a common race mod so you could run lighter valves etc.

I assume money is no issue here

[saaz]

I just found my old Ross Hanna catalogue from the early 80s that has Yoshi parts listed (and Moriwaki) for various bikes. Includes cam specs and carbs. Price list is interesting..Yoshi cams were over $300 back then. Other things like pistons were $250 complete. This includes various CB750 K1 to K7 and Kawa bits. Also GSX1000/1100...and GSX250 stage 1 cam for those inclined!

If anyone wants a copy let me know.

[Paul]

Terry, the main reason for going shim under bucket is that with very lumpy cams, the lobes can push the shim on top type shims off the top of the bucket, into the head, resulting in damaged head, bent (or broken) valves & then smashed pistons etc. Its just not worth the risk. Also as you have lumpier cams you should be getting more power, so will probably be revving higher, which makes the problem worse. The shim under bucket shims are Z650 Kawasaki parts. To see if your head needs releiving just drop the cams in (with no valves fitted) and see if they touch the head casting.

[terry]

Thanks Paul, that GS1000(s) that I sold a feller called Paul in England back in 1999 had shim under buckets with some pretty serious cam profiles, what do I need, just the shims and buckets? I'll go check ebay. Cheers, Terry. :twisted:

[Paul]

Terry
You need the shims & buckets (obviously!) but also Z650 collet retainers/valve spring caps, as they have a recess machined in them to hold the shim.
The Kawasaki part number for the "split keeper" is 12011004. I haven't got the part number for the valve spring cap. I know you can (could?) buy them from APE/MTC/Orient Express etc in the states.

"I sold a feller called Paul in England back in 1999"
I wonder who that is!
I started to build up the spare chassis, monoshock it etc, & it was stolen from the shop who was doing the conversion for me.
The bike itself is awaiting (still!) finishing off!

[saaz]

Shim under bucket should be a safer bet, as well as lighter (the shims are a lot smaller. Cams are out at shim adjustment time though, but better than a rooted motor (to use a tech term!)