Lapping a valve

[tumzoli]

I was lapping in a 16v JCB Diesel max head on Saterday, i used the normal lapping tool( peice of wood with suction cup) But my hands soon got quite sore so I modified a drill and used that,Would it still work as a drill only goes one way, Also in my workshop we have no means of pressure testing so I just grinded the shit into the valves and they look pritty seated by eye! I dunno cos shit I dont wanna put this engine back in and have the valves leak like fuck

[505197]

I bought my own old Souix valve and seat grinder, I couldn't find anyone to do valve jobs like I wanted them done. I port my share of small block Ford heads, I spend a lot of time on them and to do a valve job to suit me takes about a day. I don't do it routinely and it takes me awhile to get the feel again, it goes faster as I go along. When I'm done with the valve job I will so some more pocket porting and get it rolled in nice. I have a steady hand.

[441rider]

Filling the inlet tracks with gas valves in w/springs shows leaks fast.

[bigstiggerNo1]

does the marker subtitute for engineers blue? And which type of marker did you use?

[jacktheripped]

what I can see right near the end is the sawtooth chatter marks where someone tried to blend the seat with the port. looks like they used a pocket knife....

[seapeddler]

Valve seats should be honed and not lapped. Reason is that the lapped area is porous and burns away leaving a poor sealing surface. But who has a Serdi machine?

[bigstiggerNo1]

@seapeddler In real world hard work Course, medium then fine, then oiled fine then ajax water then done. If you have facing machine then yes honing, but normal man only has hands and time!

[seapeddler]

@bigstiggerNo1 I understand.

[UnderseaCaveman]

nice explanation of the valve marking....important to understand the valve is free to rotate (unlike a piston), therefore must lapped in to ensure concentric fit (resulting in best performance).

[4strokeonly]

well, this dumbass' car just ran a 12.56 quarter mile at 112 mph. I must have totally boned up that valve job....

[801jaguarowner]

your a dumass gring then seats

[TheChiefEngineer]

when you lap a valve there should only be a line contact.

[yamasubaruger]

Ow well I guess 4 strokes arent perfect after all tisk tisk to many moving parts,I know I am a mechanic.There are beter ideas and designs;direct injection 2 stroke's like rotax with less emission than half of the 4's in high performace apps and rotary's like the jerry Hale and Libralato.O well have fun with the valve seats,valve float and the other 20 plus parts to fatigue!

[mlatour911]

maybe the valve guide isn't 'square' to the port/valve seat, casting flaw

[belaey]

The smaller the contactcircle the better.(the closingpressure of the valve on the valveseat depends on the contactarea, the smaller the area , the higher the pressure) As long as it's located in the middle of the valveseat-contact area. Greetz

[marek0086]

your saying that less contact-area between valve-face and valve-seat gives better sealing??

[belaey]

Idd, thats what I'm saying.The thinner the contact-line the better the sealing. Ofcourse you need a full circular contact-area.

Greetz

[jasaircraft]

very interesting, makes sense, although one would normally think that having more area would seal better.

[UnderseaCaveman]

Not sure I like the "the thinner the contact-line"..... there's a limit, the metal can only withstand so much compression (without yielding, permanent deformation). But, I do agree, smaller contact area (for same force, valve spring is a constant) yields a higher contact pressure, but again "let's not permanently deform the metal, stay in the elastic operation zone of metal".

(I are an Engineer...........if you didn't get the grammar joke, then you don't get engineers, and are not one)

[lycosa2000]

You have to love engineers.. :) Please don't throw down Young's Modulus or I'll go cross-eyed. Actually, whether the contact line of the valve seal is wide or thin is rather a moot point. Staying within specified tolerances is critical and will, of course, provide the best seal. The specified tolerance is critical for not only for a proper seal, but also to provide enough force to crush carbon deposits as they form which would of course totally screw the valve seal otherwise.

[kaiedyn]

Yes, I understand. It's like when I say "I are smart". Some people just don't understand and try and correct you........frustrating isn't it.

[lycosa2000]

The thinner the contact line means a better seal, but the reason is because there is more spring force acting on the valve seat/face. The wider the contact line, the more the spring pressure is distributed across that contact line = weaker seal. Also, the exhaust valve has a ideal seat width of around 3/32" and intake 1/16" for heat transfer. (Just thought I would elaborate on what you were trying to say)

[smithraymond]

Should have shown yourself actually lapping that valve seat. We can all benefit from your experience.