Weak cyl compress

[Guest]

I have just acquired many GS 1100 parts,,, oversize Pistons, performance camshaft is what my question is about,, can I just bore out the cylinders and install the performance camshaft, or is there other modifications I need to do to make the camshaft work? Thanks

[Steve]

What year 1100?

Which model 1100?

Yes, it's important. Mainly because there were two very important differences in the 1100, along with a few minor ones. The biggest difference is whether you have the 8-valve engine in the '82-'84 1100G shafties or the 16-valve engine in the '80-'83 1100E chain-driven bikes. The pistons and cams are not compatible between those two versions.

One of the minor differences is that there were changes to the '83 1100E crank. I don't know all the details, but some of the bearings were bigger or the stator mount area was bigger, and the cranks were welded at the factory. Depending on what "performance" items you are adding, the stock crank might be OK, but I am not the expert here.

Your thread title makes me wonder, though.
Are you considering all this just because you saw low compression numbers? I have to question the history of the bike. Is this a new-to-you bike? How long since it has run reliably? If it has been sitting for a while, you need to be sure the valves are properly adjusted, then run the bike for a while to make sure the rings are seating properly, THEN get your compression readings.

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[Nessism]

What cams? Beyond a certain amount of lift different valve springs are needed. There are also possible issues like valve to piston interference that should be checked. And performance parts like those work best with a header and pod air filters. A ported head can further improve performance too. I'm assuming you are talking about a 16V engine. Not many people hot rod a 1100 8V.

[Steve]

I'm assuming you are talking about a 16V engine. Not many people hot rod a 1100 8V.

Very true. I believe there is a guy on the forum that says something like "to measure is to know".

We need to 'measure' the number of valves to offer proper advice.

Unfortunately, the original poster is new to the forum and does not realize how quickly it moves, at times.

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[bobgroger]

What cams? Beyond a certain amount of lift different valve springs are needed. There are also possible issues like valve to piston interference that should be checked. And performance parts like those work best with a header and pod air filters. A ported head can further improve performance too. I'm assuming you are talking about a 16V engine. Not many people hot rod a 1100 8V.

Except for maybe NHRA Pro Stock Bike racers. They HAVE to use 2 valve heads and stock cases. Still go 6.90\195+ in the 1/4 https://www.nhra.com/news/2019/insid...orcycle-engine