The V8 Owners Forum -

TVR Beaver wrote: .
I though all cast pistons were oval (wider over the skirts) and they expanded more round as they grew over the area that had the thickest section.. IE along the pin so expansion side to side.... I'm no expert but this is what I've always thought to be correct??

With regards to the above you maybe getting confused with them being tapered. i.e they have a bigger diameter at the skirt than the crown, this is because the crown will expand more due to the heat. They are also oval because of the way that they expand round the pin. Pistons with a high silicone content expand less and can therefore run tighter clearance, this is something that you might need to consider if you do change them. (Hypereutectic).....

http://www.hoon.tk/tech_tips/pistons.html

Yes... they expand to round and as you say.. smaller at the top as this part expands more...
But that is a point.. why dont 4.6 units do it (actualy some do but its not as common).. ?
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Another theory.. as the pistons bed in a bit and get a bit looser in the bore... how close does the con rod get to the skirt as it swings out sideways... I don't suppose it could start to kiss it as it's all expanded and hot could it?.. any whitness marks on the inside of the skirt??....

TVR Beaver wrote:Yes... they expand to round and as you say.. smaller at the top as this part expands more...
But that is a point.. why dont 4.6 units do it (actualy some do but its not as common).. ?
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Another theory.. as the pistons bed in a bit and get a bit looser in the bore... how close does the con rod get to the skirt as it swings out sideways... I don't suppose it could start to kiss it as it's all expanded and hot could it?.. any whitness marks on the inside of the skirt??....

In the case of the TVR 500, the con rod doesn't get close to the skirt.

Thinking about the small end theory, it is possible that because of the long stroke, short conrods and therefore greater angular movement of the pin in the piston, these engines may suffer greater small end wear than the other RV8's

Regards Denis

Can you get rods / pistons where the bearing is like a normal small end, so the bearing is in a bush in the rod and not the Ali piston... would this help??
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But It cant take much to make the noise happen... when they are cold they feal like a good fit so only a few microns? and obviously when new they still have to be a clearance fit when cold..
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and it still don't explain why when you use better / thicker oil (but slippier) the noise increases?

TVR Beaver wrote:Can you get rods / pistons where the bearing is like a normal small end, so the bearing is in a bush in the rod and not the Ali piston... would this help??
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But It cant take much to make the noise happen... when they are cold they feal like a good fit so only a few microns? and obviously when new they still have to be a clearance fit when cold..
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and it still don't explain why when you use better / thicker oil (but slippier) the noise increases?

I don't know of any combination of piston and rod with a bushed small end that will fit the TVR 90mm crank and block height. It is no doubt possible but considerable research would be needed and possibly some custom pistons/pins would need to be made.

On the subject of the thicker oil making the rattle louder, it is possible that the flow through the big end bearings is less and less splash is getting to the underside of the piston/pins.
The TVR rods are different to the 3.9/4.2 rod as they don't have a direct oil jet squirting at the underside of the piston through the bearing cap.

Regards
Denis

Speed 6 share same conrod design than TVR 500 and are also well know to break rods.

It is the same MCD design but machined to suit correct C/C.

Small end is so heavy and put a lot of side load on piston skirt at bottom.

May be it is possible to machine SJ SBC rods to TVR rod width ?

Getting a bit deep there I think machining width to fit.. it would take a bit of working out

the pistons as you say are only splash fed... but any oil getting there is going to get in I would have though... Millers also has the ester base so it will stop in the gap?.. I'm not sure on that one... I think I favour the fully Synthetic making it much easier to move??? Or are you meaning more for the oil cooling the underside??
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one thing I have noticed is that it takes longer to get to temp now with the full synthetic... so it must be reducing friction a lot??

I am having SBC 6 inch rods machined to TVR500 big end width. These rods have bushed small end and will be used together with Real Steel stroker pistons. They are forged Icon brand pistons.

I'll let you know if the machining works.

TVR 500 engine configuration is stupid: long stroke, short rod, tall piston...

minorv8 wrote:I am having SBC 6 inch rods machined to TVR500 big end width. These rods have bushed small end and will be used together with Real Steel stroker pistons. They are forged Icon brand pistons.

I'll let you know if the machining works.

TVR 500 engine configuration is stupid: long stroke, short rod, tall piston...

Yeah! Agree with you about the TVR configuration.
Your plan for the rods and stroker pistons sounds good and will keep it in mind for when I need to re build with my TVR 90mm crank and block.
I believe the stroker pistons are +20 thou so not a simple solution for TVR Beaver.

Regards Denis

Think I would be inclined to build a short stroke 5.0 if the size as to remain as is (V8 Dev do this) if mem serves it uses an offset ground 4.6 crank (stronger) with diff rods and pistons makes for a much sweeter rev RV8 IMHO cant say the TVR 5.0 as any appeal to me whatsoever I don't like the way they achieved the displacement along with the external balancing

SimpleSimon wrote:Think I would be inclined to build a short stroke 5.0 if the size as to remain as is (V8 Dev do this) if mem serves it uses an offset ground 4.6 crank (stronger) with diff rods and pistons makes for a much sweeter rev RV8 IMHO cant say the TVR 5.0 as any appeal to me whatsoever I don't like the way they achieved the displacement along with the external balancing

I agree if the budget permits, but often we have to use what we already have available.
In my case I sorted the external balance problem with £30 worth of Mallory metal and £200 balancing costs.

Regards Denis

I do like the look of the V8D or Rob's shorter stroke option.. but how do they get the extra dia without getting thin / close?..
Obviously they do work well as I know a few who have them and the 5.2's
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but what is the cost? (V8D's site is down)... just for a 5 ltr short engine?? .. lets face it... its only a bit of chatter... £300 for pistons would cure that??

DEVONMAN wrote: On the subject of the thicker oil making the rattle louder, it is possible that the flow through the big end bearings is less and less splash is getting to the underside of the piston/pins.
Regards
Denis

What exactly causes the 'splash'?

I doubt Counter Balance weights actually dip into the oil do they ?

Is it just oil coming out of the big end being flung about ?

"Is it just oil coming out of the big end being flung about ?"

Some of it, but over half is from the top of the engine as it makes it's way back to the sump via the valley. . .
Best regards
Mike

Of course !

That would 'splash it all over' as the great Henry Cooper said !