Cylinder Head Straightness

A blown gasket, loose valve seats, metal discolouration or a camshaft that is not turning may be the result of a warped head. It’s a good idea to quickly test such heads for warpage to determine if the head is still serviceable. All that is required is a straight edge and a filler gauge.

Remove any gaskets or carbon on the fat face that seats against the block.

Place a Straight edge firmly on the cylinder head face and see if there is gap between the straight edge and the cylinder head. If there is a gap measure with a filler gauge to determine if the warpage is within tolerance or it requires skimming. With experience you won’t even need a filler gauge to make this judgement.

This skill helps at the counter to inform the customer and make further diagnosis.

CYLINDER HEADS: Receiving the job.

My technology lecturer used to freak out each time someone calls a ‘cylinder head’ a ‘head cylinder’. There is a big difference so I’m always careful to call it by its correct name. I think he passed on the paranoia to me.

In this first part of my ‘cylinder head’ series I am going to talk about how best to receive a job to recondition a cylinder head. I found these checks very useful because I could quickly give feedback to the customer while he was still at the counter. I could advise them on thinks like: possible spares to buy, how I was going to approach the job, how long the job might take and warn them of any potential dangers (It makes good business sense to ask customers to sign a disclaimer when the risks are high or when the customer insists on a modification against your better judgment).

Customers, particularly those with a technical know-how, appreciate it when you take time to explain the logical steps that you are going to take to tackle the job. More often than not it is the mechanic who brings in the job rather than the accountant. This is one of those things that builds trust. If their job is done well, next time they come in they won’t really want to know how you are going to do it, they just want you to do it because you will have gained their confidence.

Some customers prefer to source their own spares. When it comes to commercial transporters they want there vehicles ready yesterday because downtime is costly.

So if you can predetermine some of the spares that they need to get it will save a lot of time. For instance if the cylinder head has overheated they obviously need to get a new set of valve stem oil seals for you to fit.

In the following articles I would like to highlight some signs that can help you give a general diagnosis and prognosis. Like any good doctor do not forget to verify these findings with clinical tests before administering the cure on the head cylinder –I mean cylinder head.

Unisa

I have great news that I'm truly excited about!

I have joined the University of South Africa (Unisa) to study for a Diploma in Engineering (Mechanical). A.k.a. NDEMC. It is correspondence course done in a minimum of four years and I hope to complete it in exactly that time.

Starting this program is one of those things that for a long time I kept telling myself that I have to do, but I never got around to doing it. If you've always had something on your list of New Years resolutions that always seems to get sidelined for one reason or another, then you know what I'm talking about.

Thanks to my brother and his wife I managed to register for my studies at the end of 2007 for 2008. But for some reason my registration didn't appear until now. This really had me worried. With telephone calls and emails back and forth to South Africa it was quite stressful. The most worrying thing was that I was loosing time. I literally lost a whole month and a half on study time which I have to make up for. …anyway I'm just happy that I can get started.

I don't anticipate any learning problems to begin with because I've covered the basics in other courses I've done so I should just sail through my first year and maybe second. The challenge should come in the third and fourth year.

My academic studies will certainly affect my blogging. I want to believe that the quality and the content will improve. Here is what the Unisa School of Engineering barouche said that attracted me to this particular program:

"A career in Mechanical Engineering will expose you to machines, vehicles, ships or aircraft. As part of a mechanical engineering team you will become involved in design, development and manufacture of a wide variety of components and systems. You will also be exposed to and eventually be responsible for organising the running of industrial installations and/or process plants."

Valve Seat Material

While I was doing a bit of research on cylinder heads, I stumbled upon a very interesting piece of information on AA1Car website on valve seats. This is truly one of the best automotive engineering websites in the world. It is rich in technical information and one of the key authors of this information is the one and only Larry Carley.

Here are links to his thoughts on valves and seats:

http://www.aa1car.com/library/2003/eb40332.htm

http://www.aa1car.com/library/ar993.htm

In one of his articles he explains the reason why valve seats fall out. While explaining the reason they fall out he made mention of the valve seat material.

What got my attention was the statement that cast iron valve seats are not the most suitable for making valve seat inserts. This came as a bit of a shock to me because I have been machining and installing cast iron valve seat inserts on passenger vehicles for a long time. On heavy vehicles I machined steel alloy valve seat inserts.

So I immediately wrote a rather disturbed letter Mr. Larry Carley Seeking clarification on this matter. I explained to him that the specific type of cast iron was a 'G' grade close grain cast-iron, also known by the trade name 'Mehenite'. One why to identify it is that there are no blow holes on it.

I his reply he confirmed my fears and he went on to explain that ordinary cast iron valve seats are not the best choice for today's engines. They may be okay for light duty intake valves, but they do not hold up well for exhaust valves or in engines that run at high temperatures or work hard. One exception he mentioned is performance heads with titanium valves. This information was collaborated by several automotive engineers.
Now this got me thinking: what is the fate of all those cylinder heads that we fitted with cast iron exhaust seats? How significant is this wear?

We did machine work for a number of commercial transporters on their cylinder heads (for their passenger vehicles) All our work carried a guarantee on workmanship and spares supplied yet I do not recall a job being returned for premature valve seat failure.

I may have missed it because worn valve seats were not the primary reason the head was brought in and reconditioning the seats was merely incidental.

I am starting to think that these highly esteemed gentleman where assuming that I am talking about the common low grade cast iron. All the same, to my fellow engineers out there, avoid using cast iron seats because of the metallurgical data against it.

I am working on finding the most suitable material that can be used to machine valve seats in Africa. There are some aftermarket inserts that are on offer but these are not cost effective for Africa –it would make more sense to stick to a high grade cast iron.

Does anyone out there know a suitable cost effective alternative to cast iron?

Small end recondition

 

Sequence of operation

 

 

• Tidy workstation, observe safety precautions and check accuracy of measuring instruments.
• Srip and clean connect rod assembly
• Chech that the oil galleries are clear.
• Assemble and touque  to the crrect load using a torque wrench.
• Align connecting rod in alignment fixture.
• Using a suitable jig press out small end bush on a press and remove any burrs in the rod eye.
• Drill oil holes before or after pressing in the new bush with a jig, as is suitable.
• Setup connecting rod on the connecting rod standardising machine with truing cones and then clock small end bore true to the spindle axis with a dail test indicator mounted on the boring bar.
• Measure bore with T-guage and outside micrometer and determine size to be bored to.
• Grind and lap tool to the correct angle and radius.
• Secure tool in boring bar at the correct height using a direct reading micrometer.
• Bore to size.
• Remove connecting rod from machine and clean.
•  

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Crankshaft Grinding

I was actually starting a series on cylinder head recondition as I had just written the overview but I was challenged by a colleague to come up with a step by step guide to crank grinding. I try never to back down from positive challenges so here is my take on grinding. I will be going back cylinder heads in detail in by next article. I have tried to be as comprehensive as possible but any machinist will tell you that some of the steps can be skipped depending on the type and condition of the crankshaft.

Sequence of operation

• Tidy workstation, observe safety precautions and check accuracy of measuring instruments.
• Check the thrust collars with a t-gauge and outside micrometer.
• Check journal size with an outside micrometer.
• Determine size to be ground to and availability of bearings.
• Check for bow and twist with a dial test indicator (DTI) on a magnetic base and the crankshaft on 'V' blocks.
• Crack test with a magnaflux machine.
• Stress relieve for two hours at 150 degrees Celsius. Most, including me, believe this step is not necessary.
• Mount a balanced grinding wheel on the crankshaft grinding machine. True the wheel and dress it to the correct corner radius.
• Lock the machine Chucks in position 'A'.
• Set cross slides and outboard counterweights to zero.
• Secure the crankshaft in the chucks and make sure it rotates in the same direction as it would in the engine. The crank nose normally goes into the left chuck.
• Set the front and rear journals true with a DTI.
• Set the continuous measuring gauge.
• Turn the machine on and plunge grind a journal leaving 0.03mm from finish size (Do this with a continuous supply of coolant).
• Traverse grind the journal to finish size.
• Repeat for other main journals.
• when the main journals are complete Lock the chucks in position 'A'.
• Set a plane of big-ends journals parallel to the bed using a munk.
• Move cross slide simultaneously to give the correct throw on vernier slides.
• Set outboard counterweights to balance the crankshaft.
• Complete setting the big-end journal plane using a DTI and a stoke indicator gauge.
• Balance the shaft again using counterweights.
• Set continues measuring gauge.
• Grind to size as with mains.
• Repeat for other journals in the same plane.
• Rotate index plane to the next plane.
• Set plane as with previous journals and grind accordingly.
• Repeat grinding procedure for all planes. The common four cylinder inline shaft normally has two big-end planes only.
• Dry the journal with a cloth and polish with a super-finnisher tape.
• Oil shaft and remove from the machine.
• Dynamic balance the crankshaft.

If a component is not going to be used immediately, a coat of rust inhibitor on the machined surfaces is always a good idea.

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Cyliner head Recondition (Overview)

Any cylinder head work should begin with a thorough inspection of the heads to determine if they are in fact rebuildable. The worst scenario would be to spend a bunch of money on your heads only to find that the head castings are cracked or have already been surfaced too much. Any reputable shop will Magnaflux or pressure check the castings for cracks and measure the combustion chamber volume to determine if and how much the head surface has been cut.

After inspection, the cylinder head-to-block surface should be resurfaced the minimum amount to ensure a flat sealing surface ( Please refer to previous article on cylinder head surfacing). Next hardened valve seats to combat erosion from the effects of unleaded gas should be installed. This is a fairly expensive operation but essential if you plan on getting 50,000-100,000 miles out of your rebuild. Next the valve guides and valves should be inspected for wear and replaced if necessary. A precision valve job to factory specs is next. Then the heads should be assembled with new valve stem seals with valve springs shimmed to the correct seat pressure.

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