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Valve to piston interference

  • Thread starter Thread starter doctorgonzo
  • Start date Start date
D

doctorgonzo

Guest
I had posted something on this a while back, but couldn't find the thread.

I have to have a look down the spark plug hole tonight to confirm, but pretty certain that's what's going on. I had my head decked by a local car guy (I know, I know) before sending it to APE. It came back fully assembled. Machine shop SAID they took .03 off the head, but now after assembling with a stock thickness base gasket the engine stops turning with the #4 intake fully open. It turns freely the rest of the way to that point.

I have taken the cams off and put them back in 3 times now per the manual, #1 on cam gear pointing forward, 20 pins between the #2 arrow and the #3 arrow, and each time it gets to fully open intake on number 4 cylinder and binds up.

Before I pull the head off (oh god, this sucks) and order a second, or a thicker base gasket, is it possible I might be able to fix it by degreeing the cams so that the #4 intake is fully open just before that piston hits the top of the stroke? If so how. I'm grasping at straws here as I try and avoid tearing the whole thing apart again.
 
It seems odd that only one exhaust valve would interfere, did you check the crank to see if it has been twisted? Might take only a few degrees of twist to cause a problem. You would think the valves and pistons all would make contact evenly if the crank was straight.
 
tkent02 said:
It seems odd that only one exhaust valve would interfere, did you check the crank to see if it has been twisted? Might take only a few degrees of twist to cause a problem. You would think the valves and pistons all would make contact evenly if the crank was straight.
Click to expand...

No, didn't split the cases and look at the crank. I guess the valves on one of the cylinders could be interferring with each other instead of it being piston interference. I had originally thought maybe the cam chain was binding, but like I said 3 times off with the cams and three times back on, it grabs in the exact same place. It will turn freely all the way to the point where the cam lobe is opening #4 intake fully, then dead stop. I know I am doing the cams right (or pretty sure) T mark lined up for TDC, arrows pointing correct way, 20 pins, etc... APE recut the seats, so they said they trimmed down the valve stems a bit to compensate. I thought that would set me up. As much as I hate it I guiess I am gonna have to pull the head back off and see if I can figure out what's going on.
 
You can check the crank for twist without pulling anything, measure down the spark plug hole to the tops of 1 and 4 pistons when they are half way up, the distances should be the same.
 
Stock cams? domed pistons?
So it rotates through the other cyl. strokes fine?
would spring bind be a poss.?
 
paco13 said:
Stock cams? domed pistons?
So it rotates through the other cyl. strokes fine?
would spring bind be a poss.?
Click to expand...

The head is a GS1100G, the block is a GS1000G bored out for stock 1100 pistons. The Cams are the stock GS1100 cams.

Yes, it rotates through the other cylinders fine. I did have it rotating all the way at one point when I had the timing off. The first time I installed the cams I had the exhaust rotated slightly too far forward. The arrow at "1" on the exhaust cam was below the head not even with it. When it was in that configuration, it would rotate through compression of all the cylinders, but would not start, and I could feel the pressure blowing back out the carbs as the intake opened before the exhaust was closed.... You know in thinking about it.. that makes me think the vavles are interferring with each other, not hitting the piston.
 
my first thought was valve to valve pocket.

you had cam timing off used the electric starter? then changed them . now it won't turn over all the way?
 
Last edited:
Just want to make sure you are not making the same mistake that I did the first time. :oops:
doctorgonzo said:
I have taken the cams off and put them back in 3 times now per the manual, #1 on cam gear pointing forward, 20 pins between the #2 arrow and the #3 arrow, ...
Click to expand...
You don't put 20 pins between the arrows. #1 pin is over the #2 arrow, #20 pin is over the #3 arrow, making only 18 pins between the arrows.

You have to count the pins that are directly over the arrows. (That is the part that I missed. :o )

You also need to make sure that the crank is starting on the correct mark. Make sure it's on the T 1-4 mark.

.
 
Don't be surprised if you have a bent valve.
By machining the head you have retarded the whole cam timing diagram -
the camchain length doesn't change therefore the cams will rotate backwards to accomodate the same length in a shorter space. It won't be much, you may not see it on the timing marks but it is there.
Valve to valve phasing has stayed the same - still 20t between the cams so I'd doubt if valve has hit valve.
Any time head thickness or block height is changed - and .030in is quite a change - the cams should be degreed and valve to piston clearance checked.
If you want to keep the higher compression of the machined head you may have to deepen the valve pockets.

Greg T
 
trippivot said:
my first thought was valve to valve pocket.

you had cam timing off used the electric starter? then changed them . now it won't turn over all the way?
Click to expand...

Correct. I had the exhaust cam rotated too far towards the front of the bike so the #1 arrow was slightly below the edge of the head, and it would turn freely using the electric starter. I corrected it so that #1 arrow is pointing directly at the edge of the head, and turning with a wrench hits a bind.
 
Steve said:
Just want to make sure you are not making the same mistake that I did the first time. :oops:

You don't put 20 pins between the arrows. #1 pin is over the #2 arrow, #20 pin is over the #3 arrow, making only 18 pins between the arrows.

You have to count the pins that are directly over the arrows. (That is the part that I missed. :o )

You also need to make sure that the crank is starting on the correct mark. Make sure it's on the T 1-4 mark.

.
Click to expand...

I ALMOST did that, but caught myself. I have it correct.

I am 99% sure. I have the T lined up correctly. The marks look just like the pic in the manual, but I will confirm that tonight.
 
GregT said:
Don't be surprised if you have a bent valve.
By machining the head you have retarded the whole cam timing diagram -
the camchain length doesn't change therefore the cams will rotate backwards to accomodate the same length in a shorter space. It won't be much, you may not see it on the timing marks but it is there.
Valve to valve phasing has stayed the same - still 20t between the cams so I'd doubt if valve has hit valve.
Any time head thickness or block height is changed - and .030in is quite a change - the cams should be degreed and valve to piston clearance checked.
If you want to keep the higher compression of the machined head you may have to deepen the valve pockets.

Greg T
Click to expand...

Hopeflly no bent valve. Hasn't ever hit the bind with electric starter, only hand turning, and I can feel it bind, so I stp without exerting much pressure. The engine has not run since the head was placed on.

That was kind of my question, if it's possible degreeing the cams might resolve it. If so, how much would be the max degrees I could go.

I'll add when the cams are in place correctly, there is a TON of slack between the two cams. It takes up as soon as the exhaust starts it's first turn forward. I assumed this was "normal".
 
After you get your cams positioned correctly, rotate the engine (as you have already done) to make sure nothing is binding (apparently it is :oops:). When you are assured that nothing is binding, install your cam chain tensioner, it will take up all that slack.

There should be very few times that you should ever turn the engine backwards, but you should NEVER turn it backward if the cam chain tensioner is not installed. :eek:

.
 
It has a manual tensioner. I was tensioning before I started rotation after cams installed. I am going to take a deep breathe, pull the cams off again, and start over tonight. I'll rotate the engine some just holding the chain to make sure nothing binding at the crank before I start.
 
Yes, give me a call. If you get my voice mail, leave a message with your # & I'll call you back. Ray.
 
Hey Ray, the reason I didn't call was I wanted to go through it one more time, and
I GOT IT!

The bike started tonight for the first time in about 7 or 8 months. If I wasn't so happy I'd feel like an idiot. I had it set to TDC for 2-3 not 1-4.
 
Not just running, but holding a good idle. Came off choke, in 30 to 45 seconds. Only let it run about a minute, some top end noise, a little too much rattle. Cam chain tensioner is finger tight.
 
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