24 Nov 00

Volvo Engines, Hydraulic Lifters and Solid Lifters

The following is to try to illuminate the discussion on burnt valves and different kinds of lifters/tappets. I am not a Volvo Tech but I am an engineer and I have been looking after my own Volvos for 35 years now. I have inspected / adjusted a large number of valves in many cars and motorcycles and for the past seven years I have been in, "valve-adjustment-heaven"; hydraulic tappets in my '94 850 Turbo, now with 205k kms, that do not need any adjustment. This engine still runs like new, and up to 150 km/h, it is just as fast as my '01 V70 T5. This car has never been into a Volvo Dealer for engine service after the 1000km check when the car was about a week old.

I drive about 35k kms per year and over the past 35 years we have had 8 Volvos, 7 new and one used. We keep most cars in the family for from 12 to 16 years. In 1979 some of our Volvos appeared in a Volvo Canada advertisement. If you happened to see the 1999 teen movie "Detroit Rock City" you will see our 1978 244GL, which, after 20 years in the family was sold for a $1000. to a movie company. Except for the Volvo, the movie is not worth seeing. The car is being refurbished again, as I write this, for some advertisements that some company is doing.

To the best of my recollection we have never had a valve failure, a bearing failure or any major engine problem in any of these cars. My sons and I run eight Volvos at this time, from MY '83 to MY '01, 7 of which are turbos.

Exhaust valves burn because the temperature in the cylinder gets too high and/or because the valve(s) are slightly open at the peak of the high temperature. Thus you get a high temperature gas, almost a plasma, moving past the exhaust valve lip and seat at very high speed, such that the heat transfer capabilities of the valve/ stem/ valve guide are exceeded which raises the valve temperature to the point where erosion/burning starts; in a very short time the valve fails completely. Incidentally, normally the seat is eroded as well as the valve. The edges of a burnt valve look very much like the edge of a piece of steel that has been cut with an acetylene torch.

Abnormal high temperatures in the cylinder are the result of a number of things; too lean a mixture, incorrect fuel and incorrect ignition and/or valve timing being the more important ones. (I am assuming, of course, standard Volvo engines which have not been hot-rodded, ie, too high compression and crazy valve/ignition timing, not to mention high rpms and exotic fuels.) Why are exhaust valves open too early or why do they not close completely? If the clearance is too small, or negative, between the lifter and the camshaft, then depending on the magnitude of the clearance error the valve can open too early, ie when the temp is still too high or the valve may not close completely. The other main reason for valve non complete closure is because of friction between the valve stem and the valve guide and or between the valve lifter and its carrier. Assuming the valve stem and guide are designed correctlty, proper materials, clearances, etc. the main reason for this is improper lubrication. Ditto for the lifter and its carrier. There are many, many ways of improper lubrication, but the end result is the same; the friction between the stem and the guide, or the lifter and its carrier, gets so large that the valve spring(s) cannot close the valve, hence it stays partially open. (The Mercedes 300 straight eight engine of the 50's and some motor bike engines still use desmodromic valves, ie, a camshaft/valve actuation system which not only opens the valves but closes them too; hence either no or very light springs. In the 300 Gull Wing you could spin the assembled camshaft/valve gear system by hand. They are not easy to adjust and need adjustment often.)

So it looks like this whole valve business is pretty simple. There is nothing for, "Joe Volvo Customer", to do but buy proper fuel, keep the valves adjusted and properly lubricated, and drive for half a million!

I will deal with the easiest first. Fuel. All you have to do folks is buy the highest octane fuel available from any name brand company and you should have no fuel related troubles. I have never encountered bad fuel and I have driven in every province and Territory in Canada and every state in the US except Florida and Hawaii. I do, however, try not to buy fuel that contains either ethyl or methyl alcohol or the ethers. How people can pay $50k for a car and then worry about the difference in price between 87 and 92 octane is beyond me! If you run anything but 91/92 or higher in a Volvo turbo charged engine you are asking for less power and eventual engine damage. After a certain number of occurrences of pre-ignition, the knock sensors and the computer will retard the ignition timing and reduce the manifold pressure to protect the engine; power and performance will degrade markedly.

The second easiest is lubrication. We are assuming that the Volvo engine is properly designed, with enough oil, under the correct pressure, going to all the right places all the time and that Volvo fully understood that oil both lubricates and is a heat transfer agent, ie, it cools. You can solve nearly 100% of lubrication problems, over the long haul, by having clean oil and a clean oil filter in your engine at all times! What is so difficult about that? I change my oil and filter every 5000 kms. My 850 engine looks as clean inside as the V70. In '94 Volvo recommended 8000 km oil changes for the 850. Today they recommend 12500 km oil changes for the V70. Go figure! I will change the oil in the V70 every 5000 km. For my 850 we are looking at 41 oil changes here with 5.3 litres of oil per change equals 217. 3 litres of oil at $2.50 per litre equals $543.25 over not quite seven years. I buy filters by the case from Volvo so 41 filters at $5.00 is a further $205. A little over $100. per year is very cheap engine damage insurance.

The lubricating oil environment in a modern high performance engine is complex beyond belief so I will only hit on a couple of things here. (To do this justice you would need a background in polymer and hydro carbon chemistry, fluid mechanics, high temperature physics and chemisry all of which a good lubrication engineer / engine design engineer will know at least some of.) The lubrication oil is, at various times and for various periods, in the engines operating cycle, mixed with varying amounts of, water, combustion products from oil and gas combustion including all additives, all the components of air, especially oxygen, small amounts of gasoline and dirt and for most of the time at high temperature, although some of the time in cold climates it is too cold for too long. The sump oil operating temperature normally is just below 100 degrees C. However, the oil in doing its job, is in contact with many engine parts which are of much higher temperature, for example the floating turbo charger bearing, the bottom of the pistons and the exhaust valve guides. This high temperature, over a long period of time, say more than 50 hours, changes the characteristics of the oil, produces gummy and / or carbon deposits on all manner of internal engine surfaces and will in time block or partially block small orifices and /or clearances around bearings. Some of the carbon material produced, along with the dirt which is collected makes a really great abrasive for all moving engine parts. The more abrasion that goes on the more abrasive is produced and so on. That is why a clean oil filter is so important.

You will notice that I have not mentioned synthetic oils here. Certainly the synthetic oils are more resistant to high temperature transformation than natural hydro carbon oil and they have lower coefficient of friction for equivalent grades. In my opinion, most of the junk that collects in mineral oil will also collect in synthetic oil. Therefore, use synthetic oil if you like, but change it often.

Now, for what I thought was a long solved problem and for which Volvo and I disagree: how to maintain the proper valve clearance. First a brief history to put it all in perspective. In the 1966 122S, my first Volvo, (in three days it will be exactly 35 years since I bought the 122s, which was assembled in Halifax, Nova Scotia.) the adjustment was simple; a small screw between rocker arm and push rod, adjusted with a screw driver, locked with a lock nut. Clearance measured and checked with a feeler gauge. Simple and effective. Checked and adjusted, if necessary, every 10,000 miles. (No kms those days in Canada.) Rocker cover came off with four screws. There was always some clearance left between the rocker and the valve stem end, generally around 0.008 inches. I could look it up if anyone wants the exact value. This clearance meant that there was never going to be any camshaft reason for non -valve closure, and it also allowed for valve train wear which used to affect the clearance much more than it does today. The '71 142E and 1800E were done exactly the same way. With the overhead cam engines for the 240 series cars it was almost as simple. The camshaft operated on shims sitting in bucket tappets. Measure the clearance with a feeler gauge, if out of range pull the shim, measure its thickness, if necessary put in new shim to give proper range of clearance. Always some clearance left. Same reasons as above. This system carried on throught the years. A '78 244GL, an '84 244GLTurbo and an '89 740GLTurbo+ all the same. You needed two Volvo tools, a bucket depressor and a shim removal plier. In the period 1978 to 2000 I think that I changed no more than 5 or 6 shims on all the cars. The new valve technology after the 1960's, stellite faced valves and seats and later, sodium cooled exhaust valves and for the most part very well designed engines by Volvo, made many of the earlier valve maintainence problems a thing of the past. We are now almost up to date.

Volvos five cylinder engines along with the 16 valve 4 cylinder and the 24 valve 6 cylinder, were a break with the past with respect to valve technology, they all used hydraulic tappets. All mechanical valve actuating systems described above need checking and adjustment from time to time and because of the clearance are noisy, the more clearance the more noise. More than 50 years ago, many automakers, especially in North America, decided that adjusting valve clearance was something that should be eliminated. They went to hydraulic or self -adjusting tappets or what were sometimes also called zero back-lash tappets and for the most part, are using them to this day. These tappets have several parts, essentially a piston and cylinder filled with oil which is pumped in continuously and bleeds out continuously through a bleed hole, by the engine oil pump and which applies no force on the valve until the cylinder part of the tappet is pushed down far enough in its carrier, by the camshaft, to block the oil bleed hole. Now the tappet locks up (oil is incompressible) and the tappet opens the valve, exactly the same as a solid lifter. It is not quite this simple, but you get the idea. Essentially the lifter is always in contact with the camshaft, hence the term zero back-lash or zero clearance. There is much less noise. If proper lubrication habits are not followed, see above, hydraulic tappets are sometimes prone to seizing problems, although in all the discussion of car problems in North America in the last 30 or 40 years I do not recall hearing about hydraulic tappets causing many difficulties, slow rpm engines or high rpm engines, especially if proper lubrication practices were followed. Dirty, old oil will ruin any angine in time; the only question is how long before damage occurs?

I did not know that Volvo had gone to solid lifters in 1999. When I got my new V70 three months ago, I thought that it was more noisy than the 850 engine. It sounded like valve lifter noise. A trip to the local Volvo dealer, where I bought the car and where I have been dealing with some of the personnel for more than 20 years, brought the response: "Oh no Bob you are mistaken! Your car has hydraulic lifters! What you are hearing is injector noise!" Finally I stumbled on an internal Volvo document for sales people only, on the S60, and it mentioned solid lifters, almost out of context, with no discussion at all. Needless to say the sales people do not know a solid lifter from a football. By this time I had purchased the 2001 Parts Fiches for the V70/S60 2001, the only literature I am able to buy for this car. There they were, 24 solid tappets, (not shims! tappets) of a whole range of thicknesses. The Volvo dealer still did not believe me. I guess that then they started some serious checking because they believe me now, but they think that I am flogging a dead cow.

Here is why I am concerned about this. The modern Volvo engines are designed quite differently from previous engines. No more simple cover removal to get to camshafts and/or rockers for valve clearance checking and/or adjustment. Since the hydraulic tappets do not need checking or adjustment there is no simple access to them so that if you replace them with solid tappets you have major work to check same. The top cover on these engines is the upper half of the cylinder head and is also the upper half of the camshaft carrier. Take this cover, or top half, off and the camshafts lie loosely in the lower half of their bearings. If you are familiar with Volvo tools; all 999 prefix: 5450, 5451, 5452, 5254, 5453, and 5454 and their use as described in Volvo manuals TP 31804/1 and TP 2101201 you will understand what I am talking about here. I have made a couple of sets of these tools, by the way. I have not had to use them yet on my cars. But we are not finished yet. Once we get the top off we need another tool(s), (I do not have a part number for this tool yet.) to clamp the camshafts back into the bottom half of their bearings so that they will rotate so that we can measure the clearance. You will also have to put the pulleys and belt back on. Of course, if there is valve and seat damage you will have to take the head off as well. I can see why it took Roger's shop 12 hours to replace two exhaust valves. I would suggest that this is not a home shop job unless you really know what you are doing. I would also suggest that it is not an "Average Volvo Shop That I Have Known", job either; that is why I am so worried. The chances are that what would have been a simple valve clearance adjustment in the old days will now not be discovered until engine damage occurs. Volvo has ignored the fact that there could be any potential problems here. My service book goes past the 160k km check. No mention is ever made of checking valve clearance. Remember that these engines have been on the road for a good two years.

What am I going to do? I am not sure, other than the things mentioned above regarding fuel, oil and general maintenance. These are very good engines; I may be concerned needlessly. However, I am, for the very first time since first owning a Volvo, thinking of buying the Volvo Extended Warranty, ie to extend to 7 years or 160k kms. The local Toronto dealers are having a sale until the end of December. I am going to inquire about the availability of hydraulic tappets but I do not have much hope in this regard because I have no good idea of why Volvo made this change in the first place. I can only assume that there were good, sound engineering reasons for it and that it was not dictated by some penny pinching bureaucrat, or by some silly nonsense such as reving the engine too much or too little, or because of the way North Americans drive.

I am more than a little bit pissed off at Volvo for essentially keeping this a secret from their own people and their customers. I think that we all deserve better!

All the best.

Robert A. Froebel