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MG MGB GT V8 Factory Originals Technical - Valves binding
|Further to my recent query re rough running V8. I have started to remove heads and discovered that i have a problem with binding/sticking valves, evidenced by several valve stem heads that are badly marked in fact a couple are almost mushroom/rivethead like!! They are all inlet valves. Is this a known prob. The head is a stage two, with waisted stainless valves and comp springs running in bulletted valve guides. ?? Causes. Cure. HELP.|
|D R Smith|
|Sounds like your cam may have too much lift for the springs you're using. IIRC, the stock Rover V8 springs are only good for about .370" of lift. If the cam wants more than that, it will whump the heck out of the valve stems ... because of course the valves can't go down any further than the springs'll let 'em, and the cam will bash stuff out of the way until it has clearance!|
|Is there any indication that the valve heads have hit the top of their respective pistons? Are any of the pushrods bent? Can you tell if the spring retainer has hit the top of the valve guide? Or like Ted mentioned, the valve springs could be binding - but you mention "comp valve springs" so I infer that there is some more lift capability than stock.|
Typically, if the guide seizes the valve stem, there is more of a problem with the valve closing fast enough and the piston hits the valve head and bends it (the valve head).
|How long had you been running with this arrangement of heads and camshaft before this occurred ?|
| Thanks for comments and suggestions.The car has done around 16,000 miles since engine build. No problems until recently, then rough running. The engine was built by PO to Real Steel, Stage 2 fast road spec. Using a Viper Typhoon cam which isnt a wild cam. |
A friend picked up the fact that ive been running it on unleaded and strongly suspects that the binding is due to this and recommends an additive. Total number of valves showing "hammering" marks are two, one v. badly, the other showing heavy marking. (Both inlet valves).
Push rods,cam faces, relative rocker arm contact points and piston tops are fine, as are collett position on valve stem. Will use a build lube on fitting new valves and use a fuel additive from now. Fingers crossed!! Danny.
|D R Smith|
|Danny - if the heads have been rebuilt with valves and guides of the appropriate material, you should not need an additive. I suggest you get confirmation of this from the rebuilders. You may need to look for another cause.|
Most modern maintenance outfits have seen problems like yours and when they don't relate to broken drive belts - they are frequently caused by overheating. If your engine cooling system was still full before you dismantled it - have a good look at the oilways - make sure the block and head oilways actually meet.
|Any problems due to the use of incorrect materials and unleaded should occur at the seats. As Roger says with the correct materials there is no need for additives, and this goes for the original engine as well. Having said that during a recent top-end overhaul I noticed three of my inlet valves showed slight grooving and discolouration on the end of the stem so replaced them as a precaution. There was no stiffness in the guides and the guides and stem were coated in oil. The pads of the rockers showed no wear. 16k before it started happening doesn't sound like an assembly problem, which valves are they? If towards the back and/or the left-hand bank it could be oil starvation having developed. If the heads are still on is oil flow visible at all the rockers? If the engine isn't runnable but the heads are on put a variable-speed drill on the oil pump. If the valves are out were the stems and guides coated in oil? Were they stiff to remove? Maybe they are just defective material and too soft, but I would have expected any deformation to have used up all the tappet pre-load making them noisy before it started causing rough running.|
|Paul and Roger, Thanks for comments. The valves in question slid out smoothly and were coated in oil. They are showing definite signs of "blueing" on stems at guide areas. I recently fitted RV8 manifolds so no problems with cooling,:-). Will check oil feed holes mate up on reassembly, but i would have expected probs well before this if they were misaligned? Yes, i was getting a "worn cam follower" noise prior to rough running which was presumably excessive play in clearance/s. Inlet valve nos 1 and 5. Valve seats showed normal marks for mileage covered. PO was an engineer and blueprinted the whole engine and subsequently used it for sprints for some time, so i doubt if its anything to do with build quality. I will check for oilway blockages etc on that rocker arm. Danny.|
|D R Smith|
|With my top-end overhaul I was hoping to fix a cooling system problem as well as 'tappet clatter' when hot - just one or two not all. I was successful with the former but despite changing both cam and followers (the old ones showing less the 2 thou dishing) the noise is exactly the same - but getting worse. The pre-load of the new tappets was 48 thou minimum, and putting a 20 thou feeler gauge between valve stem and rocker pad with the engine running required quite a bit of force to buth push in and pull out and made absolutely no difference to the noise, even momentarily. Another suggestion has been loose valve guides in the head, although with the rocker covers off there is very little noise with a 'listening stick' (long screwdriver) placed on each rocker and the noise seems to be coming from lower down. I have the opportunity of getting a pair of SD1 heads complete, any idea of the effect of putting these on an otherwise standard factory MGB GT V8 engine?|
|Paul, does your noise(s) change under varying load conditions (e.g., accelerating or decelerating, steady load, rev up when idling, etc)? Never heard loose valve guides cause a tapping noise. The fact that you said the noise seems to be coming from lower down and that it's getting worse leads me to believe that there's a rod bearing going bad - even though the oil pressure may not be showing low when hot. Loose wrist pins and piston slap can be hard to pin point - but unlikely to cause a clattering noise, and timing chain slap is unlikely since I'm sure it's new. Not much else to make noise within the engine unless the crank is hitting on something.|
|Sorry Paul, Im very much a V8 virgin so cant help with SD1 heads query. I would put it up as a fresh thread, someone will know im sure. If your engine is out, id be tempted to check small ends.|
|D R Smith|
|Wayne - the noise is very variable. Sometimes I can change it by minute variations of the throttle, which has always made me think it is something to do with the rod bearings or pistons but others with more experience have said not. I have heard worn big ends on another engine and that was a much deeper noise than this, mine is a clatter rather than a knocking. The hot idle immediately after a run is 20, but if left idling so the fans start cycling can drop as low as 12. But if I then switch off for half an hour or so on a hot day and restart the temp can still be on N, the idle pressure is 35, and the noise can be terrifying. But after driving at 70 or 80 mph for several minutes then idling the temp in still on N, the pressure is back down to 20, and the noise is hardly audible. The chain and gears are new as you say. All ideas and suggestions gratefully received.|
I have fitted SD1 heads on what was originally a 1975 Range Rover engine in my conversion There are no difficulties at all.
I understand the advantages are slightly bigger valves and an improvement in flow, in either the ports or combustion chambers.
my money is on the hydraulic tappets - it is unusual to get a dud new one but it does happen - IF ? you changed some and not others - the others have given up or some swarf has found its way into the hydraulic inlet - as you say the noise is an alarming rattle but quite different to a big or little end.
|A crack or leak in an exhaust manifold or header can make a ticking sound. A crack in the water pump pulley can, as well. Vee belts can make funny noises, especially if the cabling becomes exposed. I've heard harmonic balancers make a banging noise - but not ticks or clatter. Perhaps the cam bearings are not getting enough oil - what did the old cam look like? Is your new cam a "new" cam or reground? |
Grasping at straws...
|From what I have heard, sticking valves are not uncommon on newer high mileage Rovers. The guides need to be reamed. If yours was built to new Rover spec, maybe they were not reamed out large enough.|
You may want to check with a dealer for a TSB.
A freind of mine had the problem with his Disco.
|Rover is indeed having a problem with exhaust valves sticking on later engines,even low mileage cars.They have come out with a revised guide(different material and they are .250" shorter) and replacement valves also.I did a few sets for the local Rover dealer then convinced them to let me put bronze guide liners in the existing guides instead of changing the guides.For many different reasons it is a much better fix.I've done at least 6 sets this way.I've taken some pictures of the process on the last set I did and am going to give Dan a tech article on the whole shebang for the newsletter.I've never seen an intake valve stick on a Rover so I don't think that is the problem here however.Although anything is possible if the engine has run lean or if there is a lack of oil to the top end.|
|Ian - thanks.|
Roger - I replaced all of them and the cam (new) and chain and gears. The noise is exactly the same as before I started. I have also pushed a 20 thou feeler gauge between each valve stem and rocker pad one at a time with the engine running, hot, and making the noise. In every case it needed a good push to get it in and pull it out, and at no time was there any change in the noise. Had it been a tappet I would have expected the noise to quieten, even momentarily if it were a very bad tappet, then get worse when I pulled it out. With the rocker covers off in this test the noise was noticeably louder.
Wayne - the exhaust manifold *is* ticking one side but clearly identifiable as such. I've also had a problem with the drive belt and the pulley in the past but fixed that as part of the rebuild. With the heads and rocker gear back on but inlet manifold off I put a drill on the oil pump and checked oil came out of every rocker, tappet and cam bearing. The old cam looks in good condition, just a slight shading on the cams and nothing on the bearings. The old tappets have a wear dish less than 2 thou.
Kelly & Dale - I had all the valves out for a seat check and light grinding and all slid out and back under their own weight - but that was cold, of course. I have heard of the sticking valve problems but frequently use Forte flushing treatment prior to an oil change which is said to prevent it. This engine has also done 180k and started making a slight noise about 30k ago, the problems I have heard of usually apply to new or newly rebuilt engines.
The noise definitely changes with ambient temperature, the 'terrifying' noise I referred to above was in ambients in the high 20s. Yesterday in the low 20s it was nowhere near as bad even though it had been for a bit of a blast then left to idle with the fans cycling on and off. Just for the hell of it I dumped a can of STP oil treatment into it just to see what happened. I know that if these additives were any good the oil manufacturers would be using them, but I was surprised to see the hot idle rise by 10psi just while it was idling, hot running is also a few psi higher. Whether it will last or not time will tell, but there was no change in the noise.
Many thanks for all the suggestions, any more straws gratefully received.
|Paul - are your plugs all the same colour after a run ? might it be possible to detect where the problem is from discolouration ?|
My money is still on the tappets but other possibilities:
- Uneven pushrod wear - should have been eliminated by the feeler guage
- failing spark plug or break in lead - is usually a much lighter tick.
- worn rocker shaft or broken spring on shaft - again much lighter and usually constant tick.
You know what has to be done - bad luck !
I have just picked up from your message to Kelly - that you use a flushing treatment - I don't know Forte but, - the advice favours a high detergent running oil and is against the use of flushing oil - for the record.
|Plugs very close in colour, just the back two a tad darker. Noise has continued through several changes of plugs and a new cap and rotor. Exhaust note is even when cold but there is definitely an uneveness when hot and noisy, and the hot compressions are weird (some higher than normal some lower) both of which still seems to point at tappets/valves. For the record cold compressions are much more even. Rocker shafts showed no wear grooves just polishing under the rockers, springs all good, pads all flat. With a screwdriver on each rocker and against the ear there is no one rocker or rockers that exhibits a loud noise, all sound very similar, more of a general hum, with just the same quiet tick on each, which tends to point me away from the valve gear! Noted on the Forte, although acknowledged V8 specialist Clive Wheatley has been a supplier for many years.|
This thread was discussed between 27/05/2003 and 04/06/2003
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