Originally Posted by mistagoodbadguy
Ok so it sounds like umbella seals would be the way to go I just wanna make sure there no leaks if possable without rebuilding them I'm assuming replacing valve guges is something that can't be done by myself?
Guides and seats are strictly shop work this takes task specific equipment. Where iron heads are concerned the guide is made using the parent material of the head so it is simply a reamed hole. This provides a suitable bearing and heat transfer surface for the valve stem. Aluminum heads will have a pressed in guide made of a bronze alloy or of cast iron because aluminum used to make heads usually alloy 356 is not a good bearing material against the valve stem. It is also not a good seat material so there will always be a hard seat that is pressed into the aluminum. You will also find a steel spring guide that isolates and locates the valve spring from the softer aluminum. This is not required by cast iron, though for reasons of modifying the spring pressure or protecting a guide seal they may be present, but cast iron is sufficiently abrasion resistant that the spring can work in direct contact.
- Guides can be bored oversize to fit an oversized stem valve, this process can be as simple as running a piloted reamer made for this task through the guide powered from a drill motor. This is usually reserved for cast iron but can be used to salvage thick wall guides if these are used in an aluminum head.
- Cast iron heads with parent material guides can also be restored by a process of knurling and reaming to their original diameter which will allow the use of the original valves if their stems are not excessively worn and the seats are redeemable. The knurling tool looks similar to a thread tap on a long shaft. The working end is made to roll a thread pattern into the parent guide material so it had a rounded edge to the pattern rather than the taps sharp cutting edge. The idea is to squish the material into smaller diameter and the process leaves a screw thread pattern behind. Similar to the process for an oversized stem a piloted reamer which is of the original bore diameter is then passed through the knurled guide to restore the working bore size. These tools are also run from a drill motor. But they can be done on a mill or drill press but these require a more time consuming set ups. Knurling leaves behind a spiral screw pattern in the original material which holds oil to lube the guide the down side of this is it presents a direct path for oil to pass to the port so sealing the top of the guide becomes very critical. It also reduces the heat transfer surface which causes the valve to run hotter and reduces the service life on the valve. But it's very inexpensive compared to the other fixes.
- For cast iron and aluminum heads a sleeve can be pressed in these typically are made of a bronze alloy or may be cast iron. They may be a thin or thick walled, they can be a screw pattern that is screwed down a spiral made in a way similar to the knurling process but this does not lead to an oil path and maintains the stem's heat transfer surface area just with two different materials in contact with the stem. The process either starts with an over bored guide or makes the overbore depending on how the head came to the machinist. The guide material is pressed or screwed in to the bore depending on configuration and is then reamed, or honed, or ball finished to the proper smoothness and diameter. Obviously this process is the high cost one but it offers long guide life and with the proper clearances does not result in unusual oil consumption risks. However, with bronze alloy guides the lubrication requirement is very low so the use of tight positive oil control stem seals is an advantage since little oil is needed for lubrication the positive seal keeps unwanted and unneeded oil from getting down the stem to contaminate the intake mixture. Oil passes down the intake guide quite easily because the engine is pulling a vacuum on the intake system so small leaks quickly become big problems. Oil contaminates the incoming mixture because it has very little resistance to the forces that cause detonation, so when it becomes mixed with the incoming fuel and air mixture it has the effect of reducing the gasoline's octane rating.
The guides once restored become the locus of all other restoration operations on the head's valve seats, guide trimmings for larger springs, and or positive seals, height relief for additional valve lift, etc. The seats are restored with either a hard seat grinder or a Serdi machine.
The older and probably more common method found in small shops is the hard seat grinder. These use a post (mandrel) that fits into the valve guide that aligns the seat grinding tools so the seat is square to the guide and truly circular around the guide. Typical is a three (3) angle seat where a 70 degree stone is used to prepare the throat area ahead of the actual seat. The seat itself will usually be a 45 degree cut which will be the actual contact patch with the valve. The top cut will be 30 degree blend of the seat into the chamber roof. The throat and top cuts are also used to establish the width of the contact seat and its position relative on the valve seat face. Intake seats are typically narrower than exhausts because the hotter exhaust valve needs more heat transfer surface. Street engines use a wider seat than race engines because this extends the service life of the valve job. The typical hard seat grinder will have a rough and smooth stone for each angle for fast then finish grinding of the seats. The stones need frequent dressing to maintain their angles and surface quality. The tool is motor driven but this is all dedicated equipment for the job rather than something you can operate from a drill motor. The Serdi machine and other similar equipment is essentially a vertical milling machine that uses machine tool cutters to make the seats in one operation. This is a big shop piece of equipment that is very expensive.
Performance valve jobs usually include the time it takes to lap the seat and valve together for a super quality seal. These often use a 5 angle seat the purpose of the additional angles is to improve port flow through the valve having nothing to do with improved sealing. Some engines use a 30 degree contact seat the theory again being one of improved flow as the flow area of a 30 degree seat opens up faster than that of a 45 degree seat, but 30 degree seats are more subject to damage so they are not common to street engines, though it happens.
You cannot do a satisfactory seat restoration with just lapping on old seats. This process is too random to be used where major cutting needs to be accomplished and proper angles need to be maintained. You cannot get very far from the 45 degree contact seat before unusual wear and short seat life become problems.
The valves are refaced on a custom piece of equipment that is quite expensive. Assuming the stems a within dimensional tolerance the valve is chucked by its stem and run against a high speed stone wheel to put a new surface on the seat. The valve job both here and on the head results in sinking the valve deeper into the port, the effect of this is make the stem stand higher than the factory position. The stem tip which probably also shows wear from the rocker will be redressed on the valve grinding machine which will shorten the stem above the retainer. This when self guiding rockers are used can cause the rocker's guides to ride on the spring retainer so a hard cap is made too add thickness if this is a problem. Since the lock grooves are further from the bottom of the spring pocket it will be necessary to add a shim with enough thickness to restore proper spring pressure.
Hopefully you can see that a "simple" valve job is a critical set of operations and corrections using some pretty expensive machines that is not simple to achieve.