Esprit 910 cylinder head erosion?

[esprit910]

Hi All

I've just cleaned up my cylinder head and notice that there are concentric marks (very minor indentations possibly upto .001 deep) etched into the cylinder head at the top of the liners - I assume this is caused by microscopic movement of the gasket/liners over a long period of time. I dont want to reface the head as it is flat and otherwise in very good condition.
My question - is this wear normal, or must I go the refacing route and take some precious metal off the head?? Cheers Steve

[lotusguy]

Hi,


If you are certain the head is indeed flat and if the indents are merely 0.001" as you state, then I wouldn't worry about it. A new head gasket should have no trouble sealing properly. One note, the new (and I believe only available) headgaskets require the use of both a torque wrench and a torque angle meter to be properly set.

A torque Angle Meter sounds a lot more complex and expensive than it actually is. They are a simple tool costing only $15-$20 USD.
Happy Motoring! ...Jim'85TE

[Dr.Hess]

Hey Jim,
Got a source for a torque angle meter that you like? I haven't seen one at HF or Sears, but I haven't looked too close at Sears (or is it KM now?). I am doing the inner primary/clutch on my bike right now and the next major task is basically re-ringing my wife's bike, and that job needs a torque angle meter or a pencil. Thought I might get fancy with it.

Dr.Hess

[lotusguy]

Dr.Hess said:

Hey Jim, Got a source for a torque angle meter that you like? I haven't seen one at HF or Sears, but I haven't looked too close at Sears (or is it KM now?). I am doing the inner primary/clutch on my bike right now and the next major task is basically re-ringing my wife's bike, and that job needs a torque angle meter or a pencil. Thought I might get fancy with it. Dr.Hess

Hey Doc,

Here's where I got mine - www.etoolcart.com/browseproducts/Torque-Angle-Meter-OTC4554.html . I see it's gone up a couple bucks, still won't break the bank though.
Happy Motoring!... Jim'85TE

[judson]

While the head-gasket currently available is much better than older models, don't count on it...

Especially in earlier engines, the Aluminum alloy used in the 9xx series heads is very soft and prone to easy warpage (as evident by the fire-ring indenting itself into your head!).

As part of any top-end work, I'd suggest letting your machinist skim it only as much as necessary. In addition to making sure it's flat, you also have a better surface for the head-gasket to adhere.

Skimming the head isn't such a bad thing...Don't forget, the current head gasket is thicker and will cost you about 1/2 a point in compression over the older versions if so equipped.

Also, take this opportunity to check the 'nip' on each liner (s.b. .001"-.005" depending upon the engine model). If it's off or if you have a negative 'nip', no head gasket in the world will help you.

[Dr.Hess]

Hey Jim,
How does that torque angle thing work? Does that dial have to be on the bolt head? It is pretty tight where the had bolts on the Harley are with the fins and all, so I don't think I could get that dial down in there. Or does it go inbetween two extensions?

Dr.Hess

[lotusguy]

Dr.Hess said:

Hey Jim, How does that torque angle thing work? Does that dial have to be on the bolt head? It is pretty tight where the had bolts on the Harley are with the fins and all, so I don't think I could get that dial down in there. Or does it go inbetween two extensions? Dr.Hess

Doc,

It can go between some extensions. It's a matter of amplifying the inherent error, there is always some anyway with the socket and however much it may torque. With .5" extensions, this should be minimal, but if you're torqing to high numbers and are concerned that things may be twisting too much, just stop 1° shy of spec to compensate, you'll still be more accurate than using a torque wrench alone.

Remember, a screw/bolt works by actually stretching, it is this elastic tension which causes the bolt to remain tight and not simply work free from vibration etc. Also, know that all torque specs, unless otherwise noted, assume the threads and taps are dry. Rule of thumb is to cut the torque figure by 50% if the threads are wet either from lube, locktite or whatever. If you don't compensate for this lack of friction on the threads, you'll overtighten the bolt.
Happy Motoring! ...Jim'85TE

[lotusguy]

judson said:

While the head-gasket currently available is much better than older models, don't count on it... Especially in earlier engines, the Aluminum alloy used in the 9xx series heads is very soft and prone to easy warpage (as evident by the fire-ring indenting itself into your head!). As part of any top-end work, I'd suggest letting your machinist skim it only as much as necessary. In addition to making sure it's flat, you also have a better surface for the head-gasket to adhere. Skimming the head isn't such a bad thing...Don't forget, the current head gasket is thicker and will cost you about 1/2 a point in compression over the older versions if so equipped. Also, take this opportunity to check the 'nip' on each liner (s.b. .001"-.005" depending upon the engine model). If it's off or if you have a negative 'nip', no head gasket in the world will help you.

Hi,

Some good points, but I'm not sure I entirely agree. Skimming the head actually reduces the volume of the combustion chamber, this will increase the CR slightly, not reduce it, or at least make up for the additional gasket dimension.

Also, skimming the head will close the distance between the cam sprocket and the crank sprocket resulting in a slight variation in the valve timing. Lotus specs a max. skim of 0.04" for the head to still be serviceable. If the history of the car is unknown, reduce this max spec. by half to account for any possible earlier skim (I would also mark the head to record this machining for future reference to you or the next owner).

As you say, the alloy is soft, probably soft enough that the hardened steel ring on the gasket will seal up against a 0.001" gap. Just my $0.02 on the subject.
Happy Motoring! ...Jim'85TE

[lotusguy]

Dr.Hess said:

Hey Jim, How does that torque angle thing work?..." Dr.Hess

Sorry Doc,

Incomplete answer. The Torque Angle meter, like a torque wrench measures the tension imparted on a fastener. But instead of expressing it in terms of weight measure (Ft.Lbs. etc.) it expresses it in degrees of rotation (the actual degree spec is determined by taking into account the pitch of the thread, the materials used etc.). Theoretically, in a perfect system, with no unknowns, you could determine an exact number of turns a bolt would need to be under the exact ideal tension, expressed in X.00 turns.

Tests have indicated that torque wrenches alone are not consistent, or linear, especially at extreme tensions. So, the accepted method now is to use a torque wrench to pre-torque the fastener at a lower tension where the wrench is most accurate, then introduce a time component to allow the fastener to relax and shed elasticity inducing heat, and then proceed with the torque angle meter to the final tension. Often, there are multiple steps to achieving the final spec.

You should only use a torque angle meter on systems where the manufacturer of either the machinery or the gasket has computed all the variables to come up with a unique proper degree spec. You cannot convert torque angle to torque ft.lbs. as you could convert °F into °C, the torque angle spec accounts for too many differing variables to do that. If the part calls for a torque spec, use this, if it calls for a torque angle spec, use the Torque angle method, which almost always includes a Ft.Lb pre-torque. This achieves much more exact results in testing.
Happy Motoring! ...Jim'85TE

>> Edited by lotusguy on Monday 28th February 05:45

[Esprit2]

Dr.Hess said:

How does that torque angle thing work? Does that dial have to be on the bolt head? It is pretty tight where the had bolts on the Harley are with the fins and all, so I don't think I could get that dial down in there. Or does it go inbetween two extensions?

Hi Dr. Hess,
The key to properly torquing fasteners is to get the proper amount of stretch. With a nut on a stud, the most accurate way is to put a dial indicator in the end of the stud to measure how much it stretches... assuming you know how far it's supposed to stretch. However, that data isn't usually available in manuals or the "Machinery Handbook".

A torque wrench isn't the best instrument for setting critical torque since it only indicates applied load. It doesn't provide any information about how much of the applied load goes toward stretching the fastener or how much goes toward over-coming friction in the threads or between the bolt head/ nut and the work surface. It's a guessing game.

So "generic" torque tables, or unspecified torque values are traditionally assumed to to be valid only with smooth, clean, dry threads (ie, new fasteners). Under those conditions, the specified torque minus friction losses will provide the proper amount of stretch in a fastener of the specified size and grade.

Change size and/or grade and all bets are off.

Apply anything to the threads that cuts friction (oil, grease, Anti-Seize, Loctite, etc) and more torque load will go into stretching the fastener... over-stressing it. That's when, as was mentioned in a previous post, the torque load should be reduced by some amount proportional to the reduced coefficient of friction. For oil, the generic rule of thumb is 50%, but that's just a SWAG at best.

For some critical applications, the torque load is specified for "Oil Threads". In that case, it's normal practice for "Oil Threads" to be clearly stated in the torque spec. Unfortunately, Lotus doesn't do that in any of it's torque specs... you just have to know which fasteners are torqued dry and which are to be oiled.

In a Lotus engine, the head studs, main bearing panel studs and rod bolt torques all assume OILED threads, washers and head seat faces. In that case, DO NOT reduce the specified torque by 50%.

Since fastener stretch is the main goal, and there's a direct geometric relation ship between the thread helix angle times degrees of rotation, and how far the fastener is stretched, the torque angle meter is the more accurate way of measuring fastener pre-load.

Okay, the dial indicator would be more accurate, but that doesn't work for a machine screw in a blind hole, while the torque angle meter will. So engine manufacturers are moving toward the torque angle meter as the instrument of choice.

The torque angle meter is just a glorified protractor (no complex mechanism) that directly measures angular deflection of the socket. It does NOT measure tension load in the fastener. Pre-load the socket in the direction it will be turned before zeroing the meter, and socket rotation will equate to fastener head rotation. And in an indirect but pretty short path... fasterner stretch.

The meter is just a very short extension with a protractor disc attached. A free swiveling pointer is attached to a flex arm (goose neck) with a large Alligator clip. Connect it to any nearby fixed part to secure the pointer in a fixed postion. Zero the dial on the pointer. Then torque the fastener until the dial, socket and fasterner all turn the specified degrees.

The application designer will decide what stretch is appropriate for the fastener in question (size, material, grade, applied working load in service... gasket compression... etc), equate that to an angular deflection times the thread pitch to come up with a spec in degrees. The full spec usually calls for a small initial torque to be applied with a torque wrench just to take out all the slack and pre-load the parts. Then use the torque angle meter to turn the fastener the specified number of degrees. Deflection is deflection, and it won't matter if the threads are dry, oiled, Anti-Seized or Loctited.

Snap the torque angle meter directly to the socket and there will be virtually no error. However, put the meter out on the end of a long extension far from the socket and the meter will also indicate wind-up in the extension. The wind-up will cause the end-result to be short of the specified mark... ie, LESS than spec. It will NOT cause the reading to go OVER spec as noted previously.

Make every effort to install the meter directly on the socket. But if you must mount it remotely on a long extension, then if you advance carefully to the specified degrees, extension wind-up will be included in the reading and you will be short of the intended spec. Just release the pressure and allow the extension to unwind. Then read the protractor when unloaded to find out how short you are of the mark. Give it another pull or two until you get a proper reading with the load released.

Regards,
Tim Engel
Lotus Owners Oftha North

>> Edited by Esprit2 on Monday 7th March 06:17

>> Edited by Esprit2 on Wednesday 9th March 05:47

[Esprit2]

esprit910 said:

I dont want to reface the head as it is flat and otherwise in very good condition. My question - is this wear normal, or must I go the refacing route and take some precious metal off the head?? Cheers Steve

The mark is common, but it's not normal. Anything less than a flat smooth surface can compromise the gasket seal. The closer it is to the cylinder bore, the more critical it is. And the deeper it is, the more critical. If it's visible but barely noticeable with your finger nail, it may not cause a problem. However if it catches your nail as you drag it across the impression, then it's deep enough to consider milling the head.

To correct an embossed mark or corrosion, it's sufficient to cut just the gasket face. However, if the head has warped, then the entire head warps... not just the gasket face. If the bottom has a .010" bow, then the top will have a similar .010" bow. Proper milling will cut the mating faces for the cam carriers as well as the head gasket face. Failure to do so can lead to a chronic oil leak between the cam carrier and the head.

Regards,
Tim Engel
Lotus Owners Oftha North

>> Edited by Esprit2 on Wednesday 9th March 05:49

[Dr.Hess]

Thanks, Tim. I was wondering how the tool anchored for a reference. In the past, when I have pulled a HD head, I have done like the manual says and put a pencil mark on the bolt and head then turned it 90 degrees (spec). I think I'll get one of those fancy guages. BTW, Porsche designed the head/top end, so that's probably why the torque angle specs came in. Before that, it was basically put the head bolts on tight, put a box end wrench on the bolt, beat on box end with large hammer until it won't go any more.

Dr.Hess