850 Valve interference on the Piston.

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AZScott

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Started to put my 850 Commando engine together, with new barrel bored to 60 over, and new valves and head shaved to flatten it. Got the head torqued, and valves adjusted, and noticed interference at TDC. Pulled the head back off and found the intake valves were nicking the pistons on both sides. No interfierence on the exhaust side, and both intake valves left an identical dent.
850 Valve interference on the Piston.

Anyone run into this, or know how to fix ? Thinking I may need a thicker head gasket, ( was using a stock copper one ), or need to shim the barrel.
Thanks.
 
How about a die grinder and a burr. Even a Dremal. If what is shown is the extent of the interference, it should take much to bring clearence. If you are confortable with this, then the intended CR should be almost totally retained.
 
Have pocket cut into piston is the way to cure it. But first double check your cam timing as if it is slightly off it may cause the problem you have. It is however not an uncommon issue and pocketing piston is the normal way to deal with it.

Normally its done by machine not by hand.
 
AZScott said:
Started to put my 850 Commando engine together, with new barrel bored to 60 over, and new valves and head shaved to flatten it. Got the head torqued, and valves adjusted, and noticed interference at TDC. Pulled the head back off and found the intake valves were nicking the pistons on both sides. No interfierence on the exhaust side, and both intake valves left an identical dent.
850 Valve interference on the Piston.

Anyone run into this, or know how to fix ? Thinking I may need a thicker head gasket, ( was using a stock copper one ), or need to shim the barrel.
Thanks.
Click to expand...

I would suggest checking your cam timing. Piston to valve clearance is not normally an issue with an 850 unless you have had a lot of material removed from the head or your running a giant cam. Make sure all the timing marks are lined up where they should be. Jim
 
Thanks Guys, let me add I was able to rotate the crank through full cycles, and the small dent was all I was seeing.
 
With everything whirling about or slamming up and down, the clearance isn't going to be getting any better.
Time to do something about it now, BEFORE you end up with bent valves, or worse....
 
AZScott said:
Started to put my 850 Commando engine together, with new barrel bored to 60 over, and new valves and head shaved to flatten it. Got the head torqued, and valves adjusted, and noticed interference at TDC. Pulled the head back off and found the intake valves were nicking the pistons on both sides. No interfierence on the exhaust side, and both intake valves left an identical dent.
850 Valve interference on the Piston.

Anyone run into this, or know how to fix ? Thinking I may need a thicker head gasket, ( was using a stock copper one ), or need to shim the barrel.
Thanks.
Click to expand...

That shadow effect makes the ring land clearance look excessive i.e. wider than a ring almost.
Ta.
 
It's difficult to see details from the photos, but I wouldn't expect the valve to kiss the piston in this spot. Are you sure the pistons are fitted correctly with the large cutout corresponding with the larger intake valves? The pistons are Right and Left handed and also front and back critical. I would also double check valve timing.
 
850 don't actually have any valve cutout clearances on the pistons, stock anyway.

The orientation bit is interesting though,
we assumed that was somehow a pic of the back of the pistons (as in a top view, looking at the top back of the piston)

As noted previously, cam timing needs to be carefully checked out...
 
Guys thanks for the comments. Reading your posts, I went back and took a look at the timing to recheck. This is my first Norton engine,, and the diagram in my workshop manual is not very clear.
850 Valve interference on the Piston.

Looking at this again, I think I may have the cam sprocket off one tooth. I am hoping this is the problem.
 
If the head were on, checking the rockers at ' overlap ' gets you a good indication .
a meat skewer / stick down onto . into the lifters will do as well .

One closes just after the other opens . So seeing the ' overlap ' is at just before TDC
gets it at where it should be .

The Opening ( inlet ) and Closing ( zorst ) gets you the ' bias ' , more or less .

Wors Yr C.R. & Cam Type , olde boye .
 
Depending on type of use might try to advance cam a few degrees for earlier intake closing which is said to help to low/mid range spunk, other wise base plate + push rod adjusted to suit or just grind a space in crown if thickness to spare. Hope the light contact did not hurt the valve stems or guides.
 
That looks to me like the cam timing is out, the front mark on the cam gear should be one more tooth clockwise so that you can count ten chain rollers between the two white marks on each timng gear.
 
AZScott said:
Guys thanks for the comments. Reading your posts, I went back and took a look at the timing to recheck. This is my first Norton engine,, and the diagram in my workshop manual is not very clear.
850 Valve interference on the Piston.

Looking at this again, I think I may have the cam sprocket off one tooth. I am hoping this is the problem.
Click to expand...

That's exactly the problem I had a few years ago. Timing it correctly solved the interference problem. There should be 10 link pins between the timing marks on the gears.
 
Triton Thrasher said:
If the valve timing is wrong, it's retarded.
Click to expand...

Sorry- had that wrong. It's too much advance meaning the inlet opens too far before the piston has gone down out of the way.
 
Appreciate all the comments, thank you. My timing off one link appears to be the problem. It was mentioned in the posts that Cylinder Barrel Spacer might be available. With 40 plus years on the head and barrel, and not knowing how many times it was re-surfaced, I thought I would like to see if one is available for a 850 I can find one listed for a 750 "Cylinder Barrel Decompression Spacer Norton 750 Combat Commando S189" , but have not found one for a 850. Does anyone know is one is available, and who carries it?
 
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