gap between piston & valves

[KA1J]

I had to take the head from the XJ11 to a machine shop & they said there was enough warpage it should be planed.

If I use anaerobic sealant or Black RTV for the base gasket instead of using a gasket, the pistons will be that fraction closer to the valves. Accompany that with the head planing which will bring things closer, I'm wondering if the valves & piston will be in danger of touching?

[tcoop]

You don't want to use RTV for a head gasket. Head gaskets are reinforced around the piston (some sort of metal) RTV won’t hold up to the pressure. Any other joint on the engine the RTV would be fine.

[crazy steve]

You should be OK if the cut on the head is light, say .010" or less. The manufacturers generally build-in enough clearance for 'repairs' such as this. Start going more though and you may want to 'clay' the valves/pistons to make sure you're maintaining enough room. Worst case, you may have to install a base gasket, or maybe cut one out of some suitably thick gasket material to 'make up' the difference.

I have no idea what the stock clearance should be, but generally you want to see about .100" between the valves and pistons.

[tcoop]

I need to read more closely or get better glasses. (You were not talking about the head gasket.) I would go with what Crazy Steve said.

[Geezer]

I think if you leave out the base gasket, it'll likely leak like crazy. If you insist on trying this, use Yamahabond #5 to seal it not RTV that breaks down in hot oil...

Tony

[bikerphil]

I would use the base gasket anyway to be on the safe side. You probably don't want to jack your compression up too far anyway. Your cam chain will have a little more slack in it without a base gasket. JMO

[KA1J]

I would use the base gasket anyway to be on the safe side. You probably don't want to jack your compression up too far anyway. Your cam chain will have a little more slack in it without a base gasket. JMO

So many good replies. As to this one, doesn't the cam chain tensioner take up the slack so it's a non-issue?

Steve; I don't know how much they'll take off the head. I do have a gasket material I can cut to shape thanks to that UK site with the actual gasket sizes to dupe. I'd rather use the anaerobic sealer & not use a gasket if I have the choice but the problem is I don't know how much leeway there is between the valves & piston. If there's plenty I have no problems but seeing as the pistons are reliefied to mate with valves, I don't know what the tolerances are. The fellow said it wouldn't be much so I assume it's minimal. Still, it would be nice to know values...

O'course my concept of values has oft been brought to question...

[crazy steve]

So many good replies. As to this one, doesn't the cam chain tensioner take up the slack so it's a non-issue?...

Well, yes, the tensioner will take up the slack. But I think what Phil is referring to is this will also change your cam timing slightly, and there's no way to compensate for that unless you fit adjustable cam sprockets. This will retard the cams slightly, which will bring the valves slightly closer to the pistons.

As for the valve reliefs in the pistons, that's pretty standard on most motors. I seriously doubt you'll have any issue with them hitting when rolling the motor over by hand, but during operation you do need a certain amount of room as some parts will 'grow' during use and for in case there's any valve float. As an example, on some Sportster motors with certain heads, you set 'squish' which is the distance between the head and the piston crown. Going under .040" when the motor is checked cold has resulted in the piston hitting the head at operating temp and/or during high rpm use. If you can find out what the 'compressed' thickness of the head gasket is, you could clay the motor without the gasket, then do the math to see what sort of room you have. Like I said, .100" is usually the number to look for on a street motor, but as long as you're above .080" I would consider that acceptable.

[bikerphil]

Yep Steve, that and also the tensioner will run out of adjustment a bit sooner. The Vmax tensioner mod would take care of that.

It seems like a few members have been hesitant to use a base gasket after having the jugs off . Might be because it was such a b!tch to remove the old one that was on there for 30 yrs.

[TADracer]

Several years ago I installed slotted cam sprockets and fooled around with different head gaskets including copper. I have checked a few 'stock' style head gaskets after compression and they have all measured around .051" thick.

Whenever I degree-in I always check piston/valve clearance. It is not hard to do with everything installed using a dial indicator and something to push the valve down until light contact with the piston top. If you use this method you must take a measurement at 5 degree intervals starting about 20 degrees BTDC to about 20 degrees ATDC since the closest encounter rarely happens at TDC.

Closest I have ever run valves on my bike is .040" on the intakes and .065" on the exhaust side with no evidence of touching.

[KA1J]

Picked up the head today & they removed .005 although there was some pitting remaining in-between the opening for the front studs between cyl 1&2 and the same for 3&4. Where the rings on the gasket go there's no pits and the machinist felt this was sufficient to not only remove the slight warpage but make a good mating surface for the gasket.

Pre-surfacing with a thin layer of gasket yet to be removed


Post-surfacing


The studs running through those holes were rusted and the rust had packed incredibly tightly between the studs & the aluminum making it incredibly difficult to get the heads & cylinders off. All the other studs were in fine shape. I could imagine being in the front of the engine & getting salt splash, the front studs would maybe have rust issues but none of the other front studs were rusted, just these two.

Whatever the cause was, the pitting remaining on the head is where these studs were and you can see the patterned dimples from the gasket remaining after the surfacing. On the pre-surfacing photo you can see the extent the rust discoloration had penetrated and how much that etched into the aluminum. FWIW, you can see the same pattern on the cylinders but was o'course on the other side of the gasket.



So with only .005 being removed from the head it looks like I likely won't be having interference issues but what the heck happened to those studs, the rust creep and why is the pitting so severe?