crankshaft question (really wierd)

[sambo]

I bought a 1978 GS1000 engine from a guy here on the GSR, I did a top end rebuild and got the engine to run, but I've been having trouble with the far left cylinder (relative to the bike). I checked my compression and it was low on that cylinder, then I took the valve cover off and checked to make sure I could spin the buckets, i could. While I was doing this and turning the engine over by hand I noticed the the two center pistons moved up and down together perfectly, but the two outer pistons didn't. the piston on the far left was slightly behind the piston on the far right.

This doesn't seem right to me because when all the other pistons are at TDC the cam lobes for that piston are pretty much horizontal and pointing exactly away from eachother, but when the piston on the far left is at TDC the lobes are different.

Is it possible that my crankshaft could have shifted, causing that piston to be in different spot relative to the others? I hear about people welding there crankshafts for high performance engines is this what they are trying to prevent?

Thanks in advance, Sam

[Todd Horton]

Sounds like the motor has a twisted crank. Not sure where you are located but I have a 1000 motor that I could get rid of. TH

[sambo]

I'm located in New Jersey. So a twisted crank is a common problem?

[chiphead]

If my memory serves me correctly, cranks twisted on this model on a regular basis. Later models had the crank pins welded to prevent this. You may be able to find someone to re-align, balance and weld that puppy.

The general thinking back then was that this issue happened on sudden de-acceleration of the crank mass.

[Big T]

The 78s did have that crank slippage problem. Later ones used something like Locktite to cure it.
The common repair is to spot weld the pins in place. Someplace like APE can probably realign and weld it for you.

[sambo]

Thanks for all your help, so the outside pistons are supossed to go up up and down simultaneously. I guess I'm pulling the whole engine apart.

[chef1366]

Bummer dude

[madjack57754]

check out Orient Express in Freeport New York. They are a high performance shop that specializes in this type of problem, and are a lot closer to you than falicon or ape

[mark]

Thanks for all your help, so the outside pistons are supossed to go up up and down simultaneously. I guess I'm pulling the whole engine apart.

I thought I was running into problems. Good luck and enjoy.

[Todd Horton]

Sam, yes the two outside pistons 1 & 4 should be in sync with each other just like 2 & 3. Yes, the motor will have to come back apart. I have a motor with a good crank that needs a home but I'm down South. Todd Horton

[sambo]

Do a need special tools/a lot of experience to align the crank and weld it? I'm a decent welder, but don't really know how I would go about un-twisting the crank?

[Todd Horton]

Sam, The crank has to be pressed apart. I think that they use a special ground rod inserted in the rod end bores to align it and it's pressed back together and welded. TH

[sambo]

I guess I better have it done, I contacted Orient express and they told me to go to Falicon, so that sounds like the plan. Thanks, for everyones help, I love the GSR!

[Todd Horton]

Sam, good luck with Falicon, they don't like to do small jobs anymore. Every crank I have sent to them needed the rods replaced according to them. TH

[Road_Clam]

I bought a 1978 GS1000 engine from a guy here on the GSR, I did a top end rebuild and got the engine to run, but I've been having trouble with the far left cylinder (relative to the bike). I checked my compression and it was low on that cylinder, then I took the valve cover off and checked to make sure I could spin the buckets, i could. While I was doing this and turning the engine over by hand I noticed the the two center pistons moved up and down together perfectly, but the two outer pistons didn't. the piston on the far left was slightly behind the piston on the far right.

This doesn't seem right to me because when all the other pistons are at TDC the cam lobes for that piston are pretty much horizontal and pointing exactly away from eachother, but when the piston on the far left is at TDC the lobes are different.

Is it possible that my crankshaft could have shifted, causing that piston to be in different spot relative to the others? I hear about people welding there crankshafts for high performance engines is this what they are trying to prevent?

Thanks in advance, Sam

You are describing a crank that is possibly "out of phase". It does happen. Sometimes from the engine "hydrolocking" from raw fuel that weeped into the cylinder, sometimes a sparkplug chunk drops into the cylinder and so on. The only to check for a correctly phased crank is with a precision travel indicator.