Ring seal and flat tappet cams
Discussion
I have a question that's really around getting more of a 'feel' for things...
I've built an engine, it runs, and fortunately is a hydraulic roller cam, so although this doesn't apply to me, I'd like to understand better anyway.
So general advice if it's a new engine with a flat tappet cam, is to run it at 2,000 - 2,500 rpm for 20 minutes with no load on the engine upon first fire up.
The point of this being to break in the camshaft properly. That's fair enough.
My question is how this impacts ring sealing? Assuming it's a newly built engine, so a new cross hatched hone and new rings, most advice is to vary rpm a lot and ideally fairly soon to get some load on the engine to help ensure the rings seal, the extra combustion pressure of it being under load helping press the rings into the cylinder walls, and let the fresh hone do its job...
So is this initial 20 minutes of no load not going to have a negative impact on the ring seal?
As I understand it, the initial hone surface is relatively abrasive and will help 'file fit' the rings over the first 100 miles or so to ensure they seat properly and seal well. It seems that getting some load on the engine is an integral part of this, but you'd be stuck with 20 minutes of low load and relativelly little rpm fluctuation if you also had a flat tappet cam to break in... My impression is that too much low load running means you end up 'using up' this initial abrasive hone surface without taking full advantage of it because the rings didn't have enough force behind them
Or am I over thinking this, and 20 minutes isn't that important in terms of break in, and it's more like the first couple of hours of running say which is important...?
The way this relates to my build is that I'm trying to understand how critical it is to avoid running the engine at all basically until I can get it on a dyno to subject it to some load (no MOT now so need to get it run in off the road).
I'm thinking obviously it'll need to be transported to the dyno, which will mean driving on / off a trailer most likely, getting into position on the rollers and so on... How critical are we talking here timescale wise?
It's my first engine build and I'm shooting for a relatively decent specific output (for a pushrod V8) so I've been sweating the small stuff throughout the build.
Really appreciate any advice.
I've built an engine, it runs, and fortunately is a hydraulic roller cam, so although this doesn't apply to me, I'd like to understand better anyway.
So general advice if it's a new engine with a flat tappet cam, is to run it at 2,000 - 2,500 rpm for 20 minutes with no load on the engine upon first fire up.
The point of this being to break in the camshaft properly. That's fair enough.
My question is how this impacts ring sealing? Assuming it's a newly built engine, so a new cross hatched hone and new rings, most advice is to vary rpm a lot and ideally fairly soon to get some load on the engine to help ensure the rings seal, the extra combustion pressure of it being under load helping press the rings into the cylinder walls, and let the fresh hone do its job...
So is this initial 20 minutes of no load not going to have a negative impact on the ring seal?
As I understand it, the initial hone surface is relatively abrasive and will help 'file fit' the rings over the first 100 miles or so to ensure they seat properly and seal well. It seems that getting some load on the engine is an integral part of this, but you'd be stuck with 20 minutes of low load and relativelly little rpm fluctuation if you also had a flat tappet cam to break in... My impression is that too much low load running means you end up 'using up' this initial abrasive hone surface without taking full advantage of it because the rings didn't have enough force behind them
Or am I over thinking this, and 20 minutes isn't that important in terms of break in, and it's more like the first couple of hours of running say which is important...?
The way this relates to my build is that I'm trying to understand how critical it is to avoid running the engine at all basically until I can get it on a dyno to subject it to some load (no MOT now so need to get it run in off the road).
I'm thinking obviously it'll need to be transported to the dyno, which will mean driving on / off a trailer most likely, getting into position on the rollers and so on... How critical are we talking here timescale wise?
It's my first engine build and I'm shooting for a relatively decent specific output (for a pushrod V8) so I've been sweating the small stuff throughout the build.
Really appreciate any advice.
God alone knows how many Rover V8s have had their initial start-up in the same way.
If there was an issue then I suspect we'd have heard about it.
Although having replaced the cam & followers on my 3.5EFi a couple of years ago it does seem a bit harsh!
Can't see any issue with driving it around on & off a trailer & onto the dyno as the engine will be under load.
No idea about running the engine in fully with no load at all though.
If there was an issue then I suspect we'd have heard about it.
Although having replaced the cam & followers on my 3.5EFi a couple of years ago it does seem a bit harsh!
Can't see any issue with driving it around on & off a trailer & onto the dyno as the engine will be under load.
No idea about running the engine in fully with no load at all though.
Edited by paintman on Tuesday 26th April 15:50
paintman said:
God alone knows how many Rover V8s have had their initial start-up in the same way.
If there was an issue then I suspect we'd have heard about it.
I mean that is a fair point, the recommendation wouldn't exist if it was the wrong thing to do...If there was an issue then I suspect we'd have heard about it.
I suppose my question is perhaps more theoretical with a flat tappet cam, how that initial cam break in would impact quality of ring seal, more so I can get a better feel for the initial ring seating process I suppose.
Mine is in fact an LS engine, so largely similar, but yeah as I've gone with a hydraulic roller cam, I'm only concerned with the ring seal side of things but thought it'd give me a bit more insight in to the initial part of the process, as obviously all the bits I've read stress getting some load on the engine early on, and definitely not to let it idle excessively or just rev it about with no load.
General concensus seems about 100 miles and the rings are as good as they're going to get, so either they've seated well or you've worn off the abrasive edge of the hone and they're never going to seal any better sort of thing.
The intial burst of revs from startup is what starts the ring sealing process.
One driving then as suggested, vary the load and lift off for oil to get sucked onto the bores. Making the engine do some work is important.
As for the RV8, at those rpm's there will be cylinder pressure acting on the bores.
One driving then as suggested, vary the load and lift off for oil to get sucked onto the bores. Making the engine do some work is important.
As for the RV8, at those rpm's there will be cylinder pressure acting on the bores.
Edited by Boosted LS1 on Tuesday 26th April 20:42
The cam break in simply requires an "above idle" engine speed, because at low speed on a new cam, a lack of oil film (caused as a result of poor oil entrainment and high leakage due to the low speed / long time period of wiping) can result in scuffing which then develops into pitting and a rapid failure of the mating surfaces.
The rings on the other hand don't care quite so much about what speed they run at, because even idle speed is plenty fast enough in terms of velocity for them to slide on the oil held in the honing pattern.
I ususally run an engine at fast idle under no load for around 5 min just to check all is well and there are no leaks or anything untoward then i get some load on the engine asap. not WOT or anything mad, just say 25% to 50% BMEP at say 2,500 rpm.. If you have a chassis or engine dyno this is pretty easy, otherwise make sure you can drive the car right away. 20 to 30 min is enough and i'd shut off for a check of the engine and maybe an oil filter change if i was being very picky.
The rings on the other hand don't care quite so much about what speed they run at, because even idle speed is plenty fast enough in terms of velocity for them to slide on the oil held in the honing pattern.
I ususally run an engine at fast idle under no load for around 5 min just to check all is well and there are no leaks or anything untoward then i get some load on the engine asap. not WOT or anything mad, just say 25% to 50% BMEP at say 2,500 rpm.. If you have a chassis or engine dyno this is pretty easy, otherwise make sure you can drive the car right away. 20 to 30 min is enough and i'd shut off for a check of the engine and maybe an oil filter change if i was being very picky.
Max_Torque said:
The rings on the other hand don't care quite so much about what speed they run at, because even idle speed is plenty fast enough in terms of velocity for them to slide on the oil held in the honing pattern.
I ususally run an engine at fast idle under no load for around 5 min just to check all is well and there are no leaks or anything untoward then i get some load on the engine asap. not WOT or anything mad, just say 25% to 50% BMEP at say 2,500 rpm.. If you have a chassis or engine dyno this is pretty easy, otherwise make sure you can drive the car right away. 20 to 30 min is enough and i'd shut off for a check of the engine and maybe an oil filter change if i was being very picky.
Thanks M_T, I was hoping you'd chime in if I'm honest but didn't want to pester you via PM I ususally run an engine at fast idle under no load for around 5 min just to check all is well and there are no leaks or anything untoward then i get some load on the engine asap. not WOT or anything mad, just say 25% to 50% BMEP at say 2,500 rpm.. If you have a chassis or engine dyno this is pretty easy, otherwise make sure you can drive the car right away. 20 to 30 min is enough and i'd shut off for a check of the engine and maybe an oil filter change if i was being very picky.
Car will be on a dyno on the 14th May and has only had a few minutes of various unloaded rpm to check all is well and not leaking, so all is hopefully in good shape still in terms of the hone and rings.
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