One for the RV8 engine buffs.
Discussion
When rebuilding the top end it is quite well accepted that you should measure and correct the pre-load on the hydraulic lifters. The most commonly listed figures being between 20 and 60 thousands of an inch.
When required shims can be fitted under the rocker pedestals.
However I have an engine where the combination of new cam, skimmed head, cut and ground valves and some replacement valves means that some preloads are as low as .015" and others over .080". This now means I will fit adjustable pushrods.
The engine is TVR 400 with an MC1 cam so nothing extreme or race about it just a road car.
That's the preamble, now the question.
Now that I have the ability for fine adjust of the preload where should I set it?
I have read, but not fully understood, that setting it tight (.020") will improve the engines ability to rev high. The opposite being setting it loose (.060) will allow/cause the lifter to bleed down effectively acting as a rev limiter.
Your thoughts?
Steve
When required shims can be fitted under the rocker pedestals.
However I have an engine where the combination of new cam, skimmed head, cut and ground valves and some replacement valves means that some preloads are as low as .015" and others over .080". This now means I will fit adjustable pushrods.
The engine is TVR 400 with an MC1 cam so nothing extreme or race about it just a road car.
That's the preamble, now the question.
Now that I have the ability for fine adjust of the preload where should I set it?
I have read, but not fully understood, that setting it tight (.020") will improve the engines ability to rev high. The opposite being setting it loose (.060) will allow/cause the lifter to bleed down effectively acting as a rev limiter.
Your thoughts?
Steve
In an ideal world, valve seats should have been cut same height, so all installed valve heights are the same, or damn close.
I would be more inclined to aim for a higher pre-load setting rather than a low one. With a low number there is perhaps more risk of some bleed down and ending up with some lash rather than preload ?
I would be more inclined to aim for a higher pre-load setting rather than a low one. With a low number there is perhaps more risk of some bleed down and ending up with some lash rather than preload ?
stevieturbo said:
In an ideal world, valve seats should have been cut same height, so all installed valve heights are the same, or damn close.
I would be more inclined to aim for a higher pre-load setting rather than a low one. With a low number there is perhaps more risk of some bleed down and ending up with some lash rather than preload ?
I've been thinking about this. I don't think you'll get lash because there will be a spring in the follower but I know where you're coming from. The important thing is to have preload as this allows for wear in the valvetrain. I'd aim for a mid way point but wouldn't get hung up about it.I would be more inclined to aim for a higher pre-load setting rather than a low one. With a low number there is perhaps more risk of some bleed down and ending up with some lash rather than preload ?
stevieturbo said:
227bhp said:
Puma would have known.
Undoubtedly, but no sense coming to Pissheads to look for real technical content now when the admin have pushed one of the most competent members out.So the rest of may as well make s
t up.Pupp said:
Had a fairly busy week so had taken my eye off Pumagate but have just been shaking my head in disbelief at the 'we want him back' thread - talk about an own goal.
He's gone, he ain't coming back....so lets just make stuff up for technical content instead.And change thread topics while we're at it. A good thread isn't a good thread until it's been derailed lol
Pupp said:
Had a fairly busy week so had taken my eye off Pumagate but have just been shaking my head in disbelief at the 'we want him back' thread - talk about an own goal.
Indeed - just read up myself. Always a shame when you loose decent people with actual knowledge.My late father who gas flowed heads all his life wouldn't of lasted long on here either - as he tended to speak his mind and call it as he saw it!
Here's a little snippet from a magazine from the 90's on my dad:
eliot said:
Indeed - just read up myself. Always a shame when you loose decent people with actual knowledge.
My late father who gas flowed heads all his life wouldn't of lasted long on here either - as he tended to speak his mind and call it as he saw it!
Here's a little snippet from a magazine from the 90's on my dad:
I'd hate to be an engine builder, the amount of muppets wanting the moon on a stick would drive me postal! Idiots wanting massive power, total reliability, asking you have it built up ready to in the morning and then moaning about it being expensive would have me reaching for the 3/4" breaker bar...My late father who gas flowed heads all his life wouldn't of lasted long on here either - as he tended to speak his mind and call it as he saw it!
Here's a little snippet from a magazine from the 90's on my dad:
A hydraulic lifter can be thought of as a tiny hydraulic jack. Its sole purpose is to take up any slack in the valve train so the cam lobe presses directly on the follower and hence the valve. Its operation relies on the force generated inside the lifter from the engine's oil pressure being less than the valve spring pressure when the valve is shut otherwise the lifter will hold the valve open. Assuming the engine designer has done his calculations properly this will only happen if the oil pressure is abnormally high or the valve springs abnormally weak but in general it's something you can ignore.
So all you really need to ensure is that the lifter is operating somewhere inside its range of movement of the internal piston inside its bore. Shimming tight or loose will NOT make a scrap of difference to how the engine revs or generates power. Oil pressure will move the piston until it contacts the cam lobe and that's all it can do. Most engines have no provision for changing preload. The lifter should compress a bit when it's fitted and only if valve seats or other things have been changed very radically will the lifter fall outside its range of piston movement. In that case you have to machine something to bring things back into tolerance. The V8 has a preload range specified so people fret about it but with engines with no preload specified no one even thinks it's an issue.
I'd aim for 30/40 thou as a minimum and 100 thou is considered just safe at the bottom end of the piston travel but if you have adjustable pushrods then go for 60 thou and you should be right in the middle of the piston travel and safe against any eventuality.
So all you really need to ensure is that the lifter is operating somewhere inside its range of movement of the internal piston inside its bore. Shimming tight or loose will NOT make a scrap of difference to how the engine revs or generates power. Oil pressure will move the piston until it contacts the cam lobe and that's all it can do. Most engines have no provision for changing preload. The lifter should compress a bit when it's fitted and only if valve seats or other things have been changed very radically will the lifter fall outside its range of piston movement. In that case you have to machine something to bring things back into tolerance. The V8 has a preload range specified so people fret about it but with engines with no preload specified no one even thinks it's an issue.
I'd aim for 30/40 thou as a minimum and 100 thou is considered just safe at the bottom end of the piston travel but if you have adjustable pushrods then go for 60 thou and you should be right in the middle of the piston travel and safe against any eventuality.
KiaDiseasel said:
A hydraulic lifter can be thought of as a tiny hydraulic jack. Its sole purpose is to take up any slack in the valve train so the cam lobe presses directly on the follower and hence the valve. Its operation relies on the force generated inside the lifter from the engine's oil pressure being less than the valve spring pressure when the valve is shut otherwise the lifter will hold the valve open. Assuming the engine designer has done his calculations properly this will only happen if the oil pressure is abnormally high or the valve springs abnormally weak but in general it's something you can ignore.
So all you really need to ensure is that the lifter is operating somewhere inside its range of movement of the internal piston inside its bore. Shimming tight or loose will NOT make a scrap of difference to how the engine revs or generates power. Oil pressure will move the piston until it contacts the cam lobe and that's all it can do. Most engines have no provision for changing preload. The lifter should compress a bit when it's fitted and only if valve seats or other things have been changed very radically will the lifter fall outside its range of piston movement. In that case you have to machine something to bring things back into tolerance. The V8 has a preload range specified so people fret about it but with engines with no preload specified no one even thinks it's an issue.
I'd aim for 30/40 thou as a minimum and 100 thou is considered just safe at the bottom end of the piston travel but if you have adjustable pushrods then go for 60 thou and you should be right in the middle of the piston travel and safe against any eventuality.
This assumes oil pressure is always consistent and stable, and the lifter will never bleed oil too fast etc etc.So all you really need to ensure is that the lifter is operating somewhere inside its range of movement of the internal piston inside its bore. Shimming tight or loose will NOT make a scrap of difference to how the engine revs or generates power. Oil pressure will move the piston until it contacts the cam lobe and that's all it can do. Most engines have no provision for changing preload. The lifter should compress a bit when it's fitted and only if valve seats or other things have been changed very radically will the lifter fall outside its range of piston movement. In that case you have to machine something to bring things back into tolerance. The V8 has a preload range specified so people fret about it but with engines with no preload specified no one even thinks it's an issue.
I'd aim for 30/40 thou as a minimum and 100 thou is considered just safe at the bottom end of the piston travel but if you have adjustable pushrods then go for 60 thou and you should be right in the middle of the piston travel and safe against any eventuality.
It does seem some hydraulic lifters can be troublesome for RV8's given the wide range of units available claiming different things for them. And they would probably need matched to spring pressures, oil pressures etc ?
stevieturbo said:
And they would probably need matched to spring pressures, oil pressures etc ?
There should never be a need to do that. The average pushrod type lifter has an internal area of about half a square inch or a tad less. With normal engine oil pressures of say 60 to 70 psi flat out the force generated inside the lifter will only be about 30 pounds. Closed spring rates for stock 2v engines of UK size usually range from about 60 to 80 pounds. This would always be increased with performance cams so it's never going to be less than this. It takes oil pressures of well over 100 psi to cause problems whereby the lifter pressure can overcome the valve spring although this can occasionally happen with thick oil at first start up in cold weather.Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff