| Author | Message | ||
     Udo Hoffmüller Frequent User Username: udo Post Number: 73 Registered: 2-2008 |
Just a - hopfully - simple question: Introcar for instance offers hydraulic tappes for about 40 GBP each adding this comment: "This is a purpose-built tappet for the Rolls-Royce and Bentley V8 engine, not to be confused with lifters used in Chrysler and other engines, which are not correct to application and introduce the risk of engine failure." Why do they warn the customer? Is there any tecnical reason? Why are the tappets offered here poor http://www.summitracing.com/search/Department/Engines-Components/Part-Type/Lifters/Lifter-Outside-Diameter-in/0-904-in/Lifter-Style/Hydraulic-flat-tappet/Engine-Type/V8/?Ns=Rank%7cAsc&page=1 Would like to learn and understand. Best regards - Udo | ||
| Chris Browne Frequent User Username: chrisb Post Number: 66 Registered: 2-2010 |
Hello Udo, I recall reading about this a long time ago. I believe the difference is that in the "proper" hydraulic tappets there is an oil hole either to allow oil in or out of the tappet. On the cheaper American tappets, there is no such hole and although they will fit, they are not correct and are likely to lead to a failure.Hope this helps. Kind regards, Chris | ||
| Udo Hoffmüller Frequent User Username: udo Post Number: 74 Registered: 2-2008 |
Thank you, Chris, for your comment. But please have a look at the website (see link) and you will see that all the tappets offered there do have the hole. So this cannot be the reason  Best regards - Udo | ||
| Jan Forrest Prolific User Username: got_one Post Number: 282 Registered: 1-2008 |
I've seen this difference on other (smaller) engines. A few decades ago I had a Ford Escort Mk3 which used similar hydraulic cam followers. By having a seperate 'outflow hole' the oil would not pool inside the buckets thereby trapping any sludge and causing a hydraulic lock. Obviously the alignment of this hole has to be precise otherwise the operating oil pressure could (would?) be lost at just the time it is required to lift the valve(s). | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 2461 Registered: 4-2003 |
Some US tappets are OK if the seating for the pushrod is swapped over from the old one. The US generic tappets have a different radius in the push rod seat. The seating is readily swapped over by undoing the circlip at the top of the tappet. I have fitted a few from Summit in this manner without any problems. There is also sometimes an issue with the oil holes. Summit is probably the best source, but the oilways would need close inspection in case a new hole is needed to suit the Crewe tappet block. Introcar was caught out a few years back selling generic tappets under the proviso that customers swapped the pushrod seat, only to find that customers simply put them into the motor without swapping the pushrod seat, hence their higher price and explanation that they are ready to fit nowadays. Some other notable suppliers are less cautious about all this. Question: why are you replacing tappets, Udo ? It is highly inadvisable to replace any tappet unless it has a scuffed face. New tappets, or ones put back on the wrong camshaft lobe due to mixing them up, are very hard on the camshaft to the point that most manufacturers, including Crewe. warn against replacing tappets. If replacing a significant number, they always recommend a new camshaft at the same time. A cleaned-out original tappet is always preferable to a new one, and it must always be put back from where it came. Next best is good secondhand, and the worst choice is new. RT. | ||
| Udo Hoffmüller Frequent User Username: udo Post Number: 75 Registered: 2-2008 |
Thank, Jan and Richard for your explications. No, Richard, I do not replace the tappets on our cars (Shadow and TurboR). But in the german Bentley-Forum someone is going to change the tappets on the engine of a car he bought. The problem seemed to be that some of the valves did not close correctly. Whatever he did - only when lifting up the rockershaft the valves opened fully. He is going to buy from Summit. Richard, with your permisson, I would like to give him your advice in the german forum. Best regards - Udo | ||
| Jan Forrest Prolific User Username: got_one Post Number: 283 Registered: 1-2008 |
From your description Udo I would tend to think that the old followers (also called tappets or buckets) are full of crud and only need to be dissasembled for cleaning or at the very least washed in kerosene. As has been suggested this would be best done by removing them one at a time and returning each after a short soak in engine oil before removing the next. That way they can't get mixed up and put back in the wrong place. Don't forget that you can't get a full valve lift with these hydraulic followers until the engine oil is up to full operating pressure. Rotating the engine by hand or on the starter motor may give a little pressure, but hardly enough to fill them correctly. I'm a little confused by "some of the valves did not close correctly. Whatever he did - only when lifting up the rockershaft the valves opened fully". That last part sounds like the camshaft is able to move in its bearings. If it can move that much either the bearings are very badly worn or the bearing caps are loose. I would tell him to look there before blaming the tappets. | ||
| Udo Hoffmüller Frequent User Username: udo Post Number: 76 Registered: 2-2008 |
Jan, normally you are right. And I was confused, too, of his description of the symptoms. But after having opened everything he said that the tappets were not yet the original ones but already alternatives. And therefor we do understand what happened. His biggest problem is now that he will have new tappets - but without the correct stem seats because swapping of the tappets has already been done before he bought the car. And now? Best regards - Udo | ||
| Jan Forrest Prolific User Username: got_one Post Number: 284 Registered: 1-2008 |
Unless the seats are available seperately he will have to buy a full set (new or used) of replacement followers. As you and he seem to be aware Introcar have arranged for the remanufacture of many components that Crewe have stopped making. In many cases they aren't much dearer than used ones, although in this case used ones may be more desirable - if he can get them at all. | ||
| Udo Hoffmüller Frequent User Username: udo Post Number: 77 Registered: 2-2008 |
In this context another perhaps interesting question: How can I decide if the stem seat is originally Crewe or not? The background of my question: Some years ago the RR workshop in Lisboa was closed and a friend of mine bought all the stuff including RR, Bentley and Rover parts. I got a lot of parts for very cheap, among others a set of tappets. But how can I be sure that they are the Crewe ones resp. the ones with the correct stem seat? Regards - Udo | ||
| Chucky-x Unregistered guest Posted From: 91.2.176.163 |
Hi there, this is Chucky from Germany, I am the guy with the tappet issue. Udo was so kind to make me aware of this forum, maybe somebody can assist me. I found those aftermarket tappets inside my engine. One has failed completely (hole in bottom), 3 others show bottom wear, and a couple of the remaining tappets with good looking bottoms seem to have a bleed-rate of zero, so that when removing rocker-arms i.e. for servicing valve stem seals, the tappets expand and then never get compressed again. When installing the rocker shaft, those tappets never allow the valves to close, even after a week, no bleed. They seem to have the correct caps, push rods fit nicely, and when disassembled they are clean and show no wear from the inside. So I am a bit reluctant to keep the remaining tappets with good bottoms ... I found this drawing of the original tappets in the workshop manual and it looks like "4 - Valve" has a tiny hole in the middle, so I thought this hole is there to facilitate a controlled bleed-down. Is this true ? Thanks for input, Chucky  PS: tried to attach pics but did not work, sorry (Message approved by david_gore) | ||
| Alan Raggett Unregistered guest Posted From: 86.138.95.85 |
GM manufactured tappets (in Detroit) were utilised a lot as a cost effective replacement for RR V8 tappets in years gone by. GM out-sourced manufacture of these items a few years back, and quality seems to have taken a downturn. There are some excellent articles about these engines written by David Chaundy on the KDA132 website, (www.KDA132.com) and David specifically addresses this very problem of replacement tappets in his article "Problems with the V8 engine". (Message approved by david_gore) | ||
| David Gore Moderator Username: david_gore Post Number: 1047 Registered: 4-2003 |
Chucky-x, Guests cannot post images on the forum; only members are able to post images. In view of your future involvement with your car, I suggest you register as a member as soon as possible. | ||
| Chucky-x Unregistered guest Posted From: 91.2.176.163 |
Hi Alan, read the KDA article, however not helpful, only stating problems, no solutions. Hi David, yeah have registered, waiting for confirmation, Chucky (Message approved by david_gore) | ||
| Paul Yorke Grand Master Username: paul_yorke Post Number: 823 Registered: 6-2006 |
Udo, if they were original ones from a while ago, you will probably find they have a ground edge running from top to bottom. I think this allows extra oil to run from the tappet to the cam shaft. They may also have a blob of coloured paint as they were often sized to the tappet block. I would change all the tappets as failures are rare and to have so many with problems in one engine does not bode well for the rest. |
