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GS1000 rebuild opinion

  • Thread starter Thread starter mrl1000l
  • Start date Start date
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mrl1000l

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I've been researching and chatting with a few members here about rebuilding my GS1000 engine. I recently got a lot of GS engine parts from a guy locally and in the lot is an S-6 1100 head, cylinders, and pistons.

I'll come clean, I don't have a ton of money, but I'd like to get the most bang for my buck on this rebuild, and I really need the opinion of some people who have done some real engine work.

Due to the shorter stroke, I'll get 1055cc if I simple toss the complete 1100 top end on, but I will loose some compression if I don't mill the top of the cylinders a bit (0.04"). I don't have a carb bank for the larger ports and boots, so my thought is that I can just use the cylinders and pistons from the 1100, but keep the head from 1000. This will keep the compression ratio a bit more consistent and it wouldn't be all that different from just boring the stock cylinders. Would I still need to mill the top of the cylinder to deck the pistons, or would that be dangerous because the valve wells on pistons are closer to the egde of the piston then they would be with a BB piston?

I've rejetted the stock carbs (vm26) for my k&n pods and the kerker 4-1, so I think I should probably either need to get the dynajet stage 3, or just make some slight adjustments for the larger CC.

Can anyone with some experience in this give me an opinion on the matter? I'll take 2? if that's all you have, just weigh in.

Thanks for reading,
Ross
 
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With so many views and no response, I can assume that I'm entering no-man's land on this one. I'll try to pull some measurement off the two heads to see the difference in the combustion chambers to see how different they are.

Thanks for at least reading, I might move over to the rebuild section once the project gets underway.
 
I have no experience with your engine, but there are a few that do soup up the big blocks: chef1366, rapidray, blowerbike.
 
Thanks John, I remember finding your photos a few weeks back. Based on the lower CR with the 1100 pistons, it'd be silly to do this swap without going for a larger piston with a larger CR. Switching from 997 to 1055, and then stepping down on compression ratio from 9.2:1 to 8.3:1 seems like it would detune the engine rather than upgrade it.
 
Agreed.... Also I wouldn't think you'll have to do much carb work at all to cope with the extra 100cc (much less of a change than adding pods) Not sure if CR is a big driver in the world of Carb settings, I suspect it makes them a little more critical as there will be less leeway for running lean before you get pinking (knock).
 
Currently running 1100G pistons in a bored 1000 block and with a 1000 head which has been decked slightly in the past.
Works very well indeed....
The slight increase in capacity affects the carburation hardly at all.
 
Why not use the 1000 head? Should be fine. Compression ratio will go up a smig, and carbs will be big enough.
 
salty_monk said:
Remember if you deck the head I think you will have to degree the cams. :)
Click to expand...
Yes, you absolutely must degree the cams. Bit of a pita, you have to slot the cam sprockets also, but factory settings are not spot on to begin with.
 
I heard about degree-ing the cams a few times, I'm not terribly familiar with the task. I'd probably look into buy a set of slot cam gears from dynoman, as I don't have a mill or drill press on hand. I'll snoop around for some info on how to do this proper, if any one knows of a good link or tutorial, please send it along.
 
Here you go: Degreeing those cams
If you notice, the names I suggested you contact about your engine build participated in these threads.
The nice thing about this, is that you can mill your heads quite a bit and really increase your CR, cheap horsepower with no sacrifice in reliability.
Your pointer does not have to be as precise as posplayr's, he just likes to be ultra-precise.
You should also google "how to degree a cam" and learn some stuff, including why you do it.

Just a word for salty_monk: you deck the block and mill the head, two different things altogether for two different reasons. Just thought I would mention it to avoid further confusion.
 
koolaid_kid said:
Just a word for salty_monk: you deck the block and mill the head, two different things altogether for two different reasons. Just thought I would mention it to avoid further confusion.
Click to expand...

You say tomato, I say well....The head machining is not generally done on a mill. Like decking the block, it's done on a surface grinder.
A mill would however be used if an angle cut was needed - not uncommon on V8's I believe which is where the term comes from.

Either term can be used.
 
Good link, John Kat.

GregT, I stand corrected. Never heard it called that, milling the head is more commonly used. And yes, I am extremely aware of the process, having 4 decades of racing experience.
 
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koolaid_kid said:
Here you go: Degreeing those cams
If you notice, the names I suggested you contact about your engine build participated in these threads.
Click to expand...

This is great, the link in that thread that takes you further down the rabbit hole is where the meat of the degree article is. Koolaid, how many degrees off are cams from factory? just curious.

GregT said:
You say tomato, I say well....The head machining is not generally done on a mill. Like decking the block, it's done on a surface grinder.
Click to expand...

Greg, I have a favor from a friend with a mill, I will likely get my cylinder milled by him. I didn't realize that decking involved a surface grinder.

John Kat said:
Here's the thread that covers the subject in great detail:)
http://www.thegsresources.com/_forum/showthread.php?t=180351&highlight=cylinder+head
Click to expand...

John, I have read and re-read this thread a few times. It's great, I'm using many parts of it as reference for my rebuild. The one thing that I'm confused on is it seems like srsupertrap uses 73.5mm GS1000 big bore pistons with the 1100 head, because he wanted the larger intake port and the D exhaust port, but wouldn't he be loosing compression ratio from this mixture or does he make up for the loss by decking head? Is this splitting hairs? This is why I'm exploring the option of retaining the small port GS1000 head.
 
mrl1000l said:
This is great, the link in that thread that takes you further down the rabbit hole is where the meat of the degree article is. Koolaid, how many degrees off are cams from factory? just curious.
Click to expand...
Yes, the link is the best part. Posplayr tends to be a perfectionist, but he does tell it like it is.
That is the issue, cam timing is indeterminate, subject to mass production inaccuracies. When you degree your cams yourself, you are spot on.

mrl1000l said:
Greg, I have a favor from a friend with a mill, I will likely get my cylinder milled by him. I didn't realize that decking involved a surface grinder.
Click to expand...
Not sure what you mean here. Decking the block and milling the head (I am using the more common terms) both require a surface grinder. It is a very large, flat, circular grinding wheel with very precise computer aided measurements. The block or the head is mounted in a jig, then slowly lowered into the grinding wheel. Again, the purpose of decking the block is to make it perfectly flat. The purpose of milling the head is to raise compression, although it also doubles in making it perfectly flat as well.

mrl1000l said:
John, I have read and re-read this thread a few times. It's great, I'm using many parts of it as reference for my rebuild. The one thing that I'm confused on is it seems like srsupertrap uses 73.5mm GS1000 big bore pistons with the 1100 head, because he wanted the larger intake port and the D exhaust port, but wouldn't he be loosing compression ratio from this mixture or does he make up for the loss by decking head? Is this splitting hairs? This is why I'm exploring the option of retaining the small port GS1000 head.
Click to expand...
Yes, you mill the head to raise the compression. It is generally preferred to go with the larger ports, and since you have the heads already, the choice should be easy.
 
I think I understand, thanks for the clarification. I've got a lot of reading to do.
 
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