Log head Chamber depth

[Anonymous]

Got my old cut up log head six and measured the chamber depth with two valves inserted and raised them until they started to clear the chamber. Measured 4 to 5 times and got reading of 0.355 of an inch add another .040 for gasket.
Perhaps this is why standard lift is .366 at valve. I Checked because machinist said he thought I would need at least .500 before valves cleared chamber.

 

[DYNOED250]

there isnt going toi b a pproblem if there is only .355 till the valve pokes out as, the cam is never at full lift right at t.d.c you could get away with say a .390 or even bigger, it all depends on the ramp angle AND LOPE SEPERATION OF THE CAM GRIND U USE

 

[Anonymous]

Im working on the basis that I have zero deck height .400 before piston clears the gasket. machinist told me it is "possible" that the exhaust valve can be all the way down and piston at tdc (I didnt tell him the cam I was going to use).
If this is the case I may be in trouble with my .433 valve lift hitting the edge of the dished piston but I somehow doupt it considering some on this forum seem to deck everything away to there hearts content and still dont seem to have any problems.
Its just that .355 doesnt seem like much compaired to .500.
As for the valve and the LSA you confirmed what I sort of guessed from one of Executes posts and what David Vizard said on valves opening quicker initially ect, with tighter LSA.
Hey, if it hits, its bye bye engine and car.

Thanks for the Post

 

[Anonymous]

Actually now that cams dialled in i should turn it over by hand that will tell me or does the piston travel up "slightly" more when its under load at high rpm?

 

[addo]

Give yourself a 5 thou margin and it should be OK. Conservative types will say 15.

 

[xctasy]

There is enough room fellas. The valve event is not timed to open the valves fully at top dead centre.

It's a storm in a tea-cup, maties, and the only reason for clearancing the pistons would be to avoid open valves hitting the piston at top dead centre when something like the valve springs or timing chain snapped.

I'd say that someone like MustangGeezer would be real worried if it was an issue. Flat-top pistons on a 200 log with a 272 cam would be a real worry if the valves could hit the pistons.

No not of problems is given on the South American websites or from our Central or Southern American brothers (who have commerically avaliable 336 degree off the ramp cams), but I no speak Spanish or Portuguese....

For your own peice of mind, grab a little old scraped log head six of any size, and shove your cut-up head on it. Then trail build it. With the duration verses lift curve from the cam maker, you could then check each lift curve for the intake and the exhast at various pistons positions as measured in crank degrees.

On really big lifts with long durations, there is a need to do a static buildup, and then set the 'bump' with plastercine. This is done by diesel mechanics all the time.

Must guys with auto cad can calculate this using a scale diagram or by measurement if you have the values. The valves are canted to from a wedge combustion chamber, so if the piston was a flat-top (and it won't be) there is the dish, the gasket and the amount of valve open at top dead centre to factor in.

 

[DYNOED250]

i know youre talking about an log head ford six but i have a story about how easy it is to stuff up on valve to piston clearances.

My boss races speed way, and they use a 4.0 lt ford ohc engine it has flat tops and to fly cut there valve relives in the piston we put a cutting tool an old valve, and simpy bolt the head on and put the drill on the valve, the cutting tool is made to the thickness, that the valve sits out at t.d.c, and we simply turn the motor over with the drill spinning the valve and it cuts a relive in the piston. Its actually sounds very fidly but it works well once u sus it out. once the fly cuts are dun we put a set of adjustable solid rocker gear on and plasine the whole motor, we use the solids , because the hydralic lifters bleed down and give a false reading when checking clearances.
any way for those of you that know a ohc ford six the valves run on an angle , quite a large one infact, now what they done was they fly cut a motor with a standard head, they were going to use it on methanol, and so they got a hottie head built up this head was decked 120 tho, .
well long story cut short, they bolted the hottie head up, and put it on the dyno, it ran for 20 seconds and stoped it ended up with 6 bent exhaust valves, what they didnt realize was that if u deck a 4 lt head it moves the valves out to the edge of the piston when there at lift, because they run on an angle and youre effectivlt moving them closer to the piston earlier in ther travel. the valves hit the side of the fly cut made using the standard head... on an engine where the valves have to travel so far out like youre motor i could only see very wild cams causing a problem.
the hottie 4.o ohc head had to have the intake valves removed for it to be machined as the machine actually cut into the cornor of the valve seat, so it was all ready out side the surface of the head even when it was in its seat.

 

[MustangSix]

 

[addo]

Great! Now if we can input some parameters, scale it and slow it down some... :roll:

 

[Anonymous]

Thanks for the responce Fellas Im not concerned anymore. Mustangsix I need to see what the valves do at much higher revs (kidding).

 

[Anonymous]

I just managed to get the bare engine and gear box in last night with the rain blowing in the garage the whole time and me lying in the oil green stuff and puddles. Saturday the sump leaked at the flywheel end second time used more sealant at the ends and seems OK now. Ill set up the rocker assembly and valves next.