The V8 Owners Forum -

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wokingwedger wrote:

mgbv8 wrote:

wokingwedger wrote: Mike, I am not sure why valve lift will change.

The cam lift is the same the raio of 1.6 is the same,

I have just lowered the rockershaft and the push rod and top of the lifter.

Are you saying they will pump up more because there is less oil in them ?

I assume there is less oil in them, or it will be compressing the valve spring.

The lifters (if working ok) should pump up solid at X rpm. The lifters dont maintain the pre load gap when running fast.
This gives you the full lift from the cam at higher rpm. My Rhodes lifters pump up hard at around 3000 rpm. You can see this in a torque spike at that rpm on the dyno.
The pre load gives you more clearance (bigger tappet gap) at low rpm when the lifters cant pump up fully.

So its cam lift x 1.6 = ?? at low rpm for valve opening.
And Cam lift + your 100 thou x 1.6 at higher rpm for max valve lift.

Too much pre load can lead to bent push rods if you havent got all the clearances set right.

Ahh, so if they pump up every time its revved, they also bleed down every time the revs drop, so I should have the reduced amount of oil and increased pre comperession I expect (for good or bad) as its been revved a few times.

So are you saying that when revved the lifter will fill until the spring clip stops it ?

So are you saying that when revved the lifter will fill until the spring clip stops it ?

YEP!
Thats how it works...

wokingwedger wrote:I have been doing a bit of experimenting with preloads, trying to get rid of a 'rattle on over run' that I, and approx 50% of 5.0 litre TVR RV8s appear to have.

I have adjustable pushrods and set all preloads to 50 thou, but due to limited adjustment on the pushrod had to use a 35 thou shim under the pedestal. The rattle was still there (1200 rpm only as previously)

There may be other reasons for the noise but as I say I have been trying different preloads.

Question for all those in 'the know' :-

I have removed the shims thus increasing preload to approx 100 thou.
How long will it take for the lifters to evacuate their excess oil and settle at their new compressed height. Will each one do it whenever the engine is turned off and each lifter is left in its compressed state. I have barred the engine over a few turns, leaving a hour or so in between.

Before having the cam changed I noticed that when trying to measue lift at the rocker arm , the dti kept winding back, presumably due to bleed down of the lifter.

The noise is still there, but I without an answer to the above I am not sure things are operating as I intended. The car is running superbly by the way !

I just read this again!
You should not need to shim the pedestals if your pushrods are the right length to start with. you cant measure lift at the rocker arm unless you have a mech cam and solid lifters.

Hi
"Bag of bolts" and resonates at "1200 ish rpm" makes me think something is loose and rattling
Have you checked
Baffels under rocker covers are not loose?
that the flywheel flex plate bolts are tight?
Clutch cover/ torque converter bolts are tight?
That cover on the lower half of the bell housing is done up OK?
Are the oil pump pickup and strainer firmley attached and clear of the sump?
Have you a spanner/ socket, pair of pliers, tea spoon on top of the valley gasket under the inlet manifold?
Are all the heat shields, clamps and stuff attached to the exhaust manifolds done up properly and not broken?
Are all the front pullies bolted up tight and all the spacers on the mounting brackets pinched up properly?
Has it got catalitic converters? have they faller apart inside?
From what you have had done so far I would return the lifters to spec (drain them down and return then to the normal pre load, preferably slap in the middle) and after checking the can chain hasn't stretched to Bu&&ery leave well alone I don't think it is cam or lifters.
Check all tha above and anything else that bolts to the engine to see if it is loose.
Then it is either piston slap (quite likley as it is a 5 liter) in which case live with it or con rods rattling together (which personally I think a bit far fetched).
Best regards
Mike

kiwicar wrote:Hi
"return then to the normal pre load, preferably slap in the middle

It is definately related directly to engine revs. No doubt about it !

What would you consider to be best 'slap in the middle' pre load ?

V8D say .040 to .100
RPI say .020 to 0.050

Hi
I would say in the region of 60 to 70 thou, I don't tend to take notice of what RPI say, V8 Dev have a good reputation but what does the TVR manual say? because I would go with that or Rover who after all specked the lifter in the first place.
If it is engine rev related, not at 1/2 revs then it isn't tappets.
With regard the stethascope and isolating noises some times you can isolate them by using a sandbag or big rubber mallet to dampen the noise, stick the end of the stethascope on the block in the area you are investigating, with the engine running hold the sand bag/ big rubber mallet onto the block and see if you can make the noise in question dissappear/ reduce by holding the sand bag against an area of the block if you do get a reduction move the stethascope closer to that area and try again, if you get more reduction then you may well be close!
Best regards
Mike

mgbv8 wrote:

wokingwedger wrote:

mgbv8 wrote:
The lifters (if working ok) should pump up solid at X rpm. The lifters dont maintain the pre load gap when running fast.
This gives you the full lift from the cam at higher rpm. My Rhodes lifters pump up hard at around 3000 rpm. You can see this in a torque spike at that rpm on the dyno.
The pre load gives you more clearance (bigger tappet gap) at low rpm when the lifters cant pump up fully.

So its cam lift x 1.6 = ?? at low rpm for valve opening.
And Cam lift + your 100 thou x 1.6 at higher rpm for max valve lift.

Too much pre load can lead to bent push rods if you havent got all the clearances set right.

Ahh, so if they pump up every time its revved, they also bleed down every time the revs drop, so I should have the reduced amount of oil and increased pre comperession I expect (for good or bad) as its been revved a few times.

So are you saying that when revved the lifter will fill until the spring clip stops it ?

So are you saying that when revved the lifter will fill until the spring clip stops it ?

YEP!
Thats how it works...

Surely if it does this it has 'gone solid' as it cant expand further and wont compress due to the oil pressure and therefore is no longer acting as a 'hydraulic' lifter

Surely to 'take up the slack' as I thought they were intended to do, they need to act between the cam and the pushrod, not lock up against the retaining clip.

They are hydraulic and work as hydraulic for most of the time.... what the guys have been trying to explain is that at high rpm (and possibly with high oil pressure) the lifters finally pump up and start acting a bit like solid ones, therefore the valve is never fully shut because they've extended through the usual pre-load position which gives a closed valve, hence the risk of valve/piston contact in extreme cases when running very high preload..... or you compress the valve springs so much that they become coil bound and then you bend your pushrods...

This is also why running a small lifter preload is good because you can minimise the amount the lifter can pump-up... allowing exploitation of higher rpm etc, however in a std engine having some pre-load can be good (well you need some regardless else you'll have clearance and valve train noise) because the pump-up of the lifters acts as a crude rev limiter....

I think what I've described is correct.... that's how I understand it anyway.

Remember this is not a static system, at 6000 revs the lifter is being loaded and unloaded 50 times per second, it's height is dictated by how fast oil can flow out of a hole about 1mm in diamiter while it is hit by the rising slope of the cam lobe. If the lobe is aproximatly 90 degrees in duration but it sits in it's bore for about 440 degrees so it has no issue getting oil into the lifter. Getting it out however is another issue. . . It has about 0.0025 of a second to get about 1/8 cc of oil out of that hole, that is about 50cc/sec through a hole about 1mm in diamiter, that is one h3ll of a flow rate for a hole that size, that is why I said above that oil viscosity was one of the primary funtions of how much height the tappet has at higher revs (and why I find it so frustrating when people change to aa lower viscocity oil and expect it all to just work as normal without thinking about what they are doing).
You can also see from the above that engine oil pressure has virtually no influance on lifter pump up, the pressures involved to get 50cc/sec through a 1mm hole make a few tens of PSI from the oil pump insignificant, oil flow and a constant supply are esential but pressure is not.
Best regards
Mike

Oh and just to make life interesting the oil, when under these pressures, is compressable, it is allowed for in the cam lobe design but it means that when cam grinders recommend a certain valve/ piston or retainer / guide clearance, they mean it and it is why people are prepared to push these clearances further with a mechanical cam and lifter.

mk1storm wrote:They are hydraulic and work as hydraulic for most of the time.... what the guys have been trying to explain is that at high rpm (and possibly with high oil pressure) the lifters finally pump up and start acting a bit like solid ones, therefore the valve is never fully shut because they've extended through the usual pre-load position which gives a closed valve, hence the risk of valve/piston contact in extreme cases when running very high preload..... or you compress the valve springs so much that they become coil bound and then you bend your pushrods...

This is also why running a small lifter preload is good because you can minimise the amount the lifter can pump-up... allowing exploitation of higher rpm etc, however in a std engine having some pre-load can be good (well you need some regardless else you'll have clearance and valve train noise) because the pump-up of the lifters acts as a crude rev limiter....

I think what I've described is correct.... that's how I understand it anyway.

I agree in principle with the above. But it depends how you set the valve train up and what type of lifters you use. The stock Rover 3500 V8 in the factory built MGB V8 is an example. At 5800 rpm my factory engine would flutter when the lifters pumped up fully as the valves were being held slightly open. A crude rev limiter. I ditched these and fitted Rhodes lifters with a bigger cam, adjustable push rods and some head work. I set it up so the valves would hit full lift and still give me about 10 thou pre load. This got the engine to rev easily to 7000 on the dyno (for testing only I might add, and to well over 8000 rpm for a couple of seconds when an axle let go)

The idea is to understand a few basic things. For what I use my car for all I'm interested in is what goes on when the engine is flat out for 10 seconds on the drag strip. The last thing I want is valves not closing fully when I'm running boost and nitrous.
At hot idle my valve train does not rattle. It makes a noise that sounds like a handfull of ball bearings being rolled down a thin 10 foot steel tube which is inclined at 45 degree's. a sort of metallic rushing noise ???
I hope you can imagine that sound?

I use 20/50 oil as well.

As your issue seems rpm related. what oil pressure do you read at the problem rpm ??

Is this car driveable??

If so I would be happy to have a listen to it if you have the time to drive to a small town near Silverstone. I'm about 20 mins from M40 J9.

I'll be happy to have a poke around with you to see if we can find the problem.

I'll be back in the UK in early November.

regards
Perry

mk1storm wrote:They are hydraulic and work as hydraulic for most of the time.... what the guys have been trying to explain is that at high rpm (and possibly with high oil pressure) the lifters finally pump up and start acting a bit like solid ones, therefore the valve is never fully shut because they've extended through the usual pre-load position which gives a closed valve, hence the risk of valve/piston contact in extreme cases when running very high preload..... or you compress the valve springs so much that they become coil bound and then you bend your pushrods...

This is also why running a small lifter preload is good because you can minimise the amount the lifter can pump-up... allowing exploitation of higher rpm etc, however in a std engine having some pre-load can be good (well you need some regardless else you'll have clearance and valve train noise) because the pump-up of the lifters acts as a crude rev limiter....

I think what I've described is correct.... that's how I understand it anyway.

I also think that they work in the way that you have described, I don't think that the pre-load will make any difference to how the valves operate whilst the lifters are operating in 'normal mode'

I don't think the the oil system is capable of knowing when the revs are approaching 5800 RPM so that they can pump up the lifters, I think that the valves start to float with the standard Rover setup at this RPM and it is this that is allowing the lifters to pump up. Basically the oil pressure will immediately pump the lifter as soon as there is no valve spring load on it, this then holds the valve open which kill the engine power so that the engine will rev no higher. This is when the lifter preload gets important, if it is set to 80 thou then it will hold the valve open 80x1.6 thou (3.2mm)....This could easily be enough to allow a piston to hit a valve in a modified engine. I run adjustables and have set my preload to 20 thou.

AJMHO!

Apologies if he above has already been posted up in this rather long thread!

sidecar wrote:

mk1storm wrote:They are hydraulic and work as hydraulic for most of the time.... what the guys have been trying to explain is that at high rpm (and possibly with high oil pressure) the lifters finally pump up and start acting a bit like solid ones, therefore the valve is never fully shut because they've extended through the usual pre-load position which gives a closed valve, hence the risk of valve/piston contact in extreme cases when running very high preload..... or you compress the valve springs so much that they become coil bound and then you bend your pushrods...

This is also why running a small lifter preload is good because you can minimise the amount the lifter can pump-up... allowing exploitation of higher rpm etc, however in a std engine having some pre-load can be good (well you need some regardless else you'll have clearance and valve train noise) because the pump-up of the lifters acts as a crude rev limiter....

I think what I've described is correct.... that's how I understand it anyway.

I also think that they work in the way that you have described, I don't think that the pre-load will make any difference to how the valves operate whilst the lifters are operating in 'normal mode'

I don't think the the oil system is capable of knowing when the revs are approaching 5800 RPM so that they can pump up the lifters, I think that the valves start to float with the standard Rover setup at this RPM and it is this that is allowing the lifters to pump up. Basically the oil pressure will immediately pump the lifter as soon as there is no valve spring load on it, this then holds the valve open which kill the engine power so that the engine will rev no higher. This is when the lifter preload gets important, if it is set to 80 thou then it will hold the valve open 80x1.6 thou (3.2mm)....This could easily be enough to allow a piston to hit a valve in a modified engine. I run adjustables and have set my preload to 20 thou.

AJMHO!

Apologies if he above has already been posted up in this rather long thread!

I agree entirely with Sidecar.

My standard lifters don't bleed down even when the engine is stopped and the open valves stay open almost indefinately when stopped. If they didn't, you would get an enormous rattle on start up every time, which I don't and nor do most RV8's.

The Rhodes lifters have a constant bleed down hole which reduces valve lift until the point where the bleed is not large enough to release the oil quickly enough and then give full lift.

I'm not sure how high rev lifters deal with the valve float matter.

I am keen to find out the cause of the rattle on the TVR 500 lump but cannot see that bleed down of the lifters for a few seconds is the cause, given that mine stay pumped when the engine is stopped and when there is no oil pressure. My guess is that its a chatter/resonance within the engine and could be related to the fact the these engines are externally balanced, but just a guess.

Cheers Denis

I don't think the the oil system is capable of knowing when the revs are approaching 5800 RPM so that they can pump up the lifters, I think that the valves start to float with the standard Rover setup at this RPM and it is this that is allowing the lifters to pump up.

Its not really oil related... Its time / rpm related depending on the viscosity of the oil you are using and the temperature of the oil at that time as this effects viscosity.

The lifters take oil in and let oil out in their up and down cycles. When the cycle gets too fast for them to drain they cant let oil out fast enough and they stay pumped up. As the engine rpm increases so does the oil pressure. This means that each shot of oil from the lifter gallery contains oil at a higher pressure. When the amount of oil going "in" to the lifter equates to more than the lifter can drain at that rpm it stays full !!!


I think that the valves start to float with the standard Rover setup at this RPM and it is this that is allowing the lifters to pump up

You are saying that the relief in tension on the lifters due to valve bounce allows the lifters to fully prime and give full lift which in turn allows the valves to stay more open than they should ??

Maybe thats the way Rover designed it ??
Either way, on the stock setup the valves being held a bit open at this rpm does the job of limiting rpm??

I think we need to do the Math on this one.
The internal area of the lifter plunger is about 0.2 sq inches. Therefore at say 50 lb/in2 gallery oil pressure, the upward force is 10 lb. The valve spring fitting load is 75 lbs which gives pushrod resistance load of 75 x 1.6 = 120 lb.
Therefore the normal pushrod load far exceeds the pump up force/ability of the lifter and pump up therefore cannot occur until the push rod load is removed/reduced by valve float action at high revs.

An effective rev limiter designed by Buick for the RV8 back in the 50/60's and we still depend on it.

Cheers Denis