Citroen C1, Peugeot 107, 108 & Toyota Aygo Owners Club. (Discount code for CityBugStore: C1OC)

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PostPosted: Mon Mar 09, 2020 3:27 pm 
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Cam Timing

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Theory:


I began experimenting with cam timing about a year ago, when I first had a go at the exhaust ports.

I got the idea reading about tuning the 1.8 engine in an MX-5 where the cam sprockets can be rotated to make use of a different timing slot intended for another engine, marginally altering the timing on the MX-5 to increase performance at the expense of fuel consumption & smooth idle characteristics.

Unfortunately the cam sprockets in the 1KR-FE don't offer such trickery but their 36 teeth do allow a decent enough resolution to explore the idea...


These are the standard timings for the 1KR-FE:

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Toyota has published a useful description of the VVTi timing conditions on the 1KR-FE, which does a much better job of explaining the variable intake side of things than I can:
https://toyota-club.net/files/faq/16-01 ... _4_eng.htm

The timing of the inlet cam varies based on engine condition and is controlled by the ECU;
the exhaust cam timing is mechanically set so we can in theory play with this fixed value.

By moving the exhaust cam back a tooth (on the timing chain) you're retarding the cam by 10 degrees.

The engine timing is stated relative to the crank so, as the engine rotates twice for every full rotation of the cam, this 10 degree change in cam angle equates to 20 degrees of exhaust timing retardation - This is quite a drastic change to the timing but it doesn't render the engine inoperable.


What retarding the exhaust cam does is cause the exhaust valves to stay closed for longer into the power stroke so the engine generates more torque lower down in the rev range - the explosion is pushing on the piston for longer, at a time when the engine is turning slowly with little momentum.
Conversely, generating top end power relies on engine speed & momentum (pushing the piston in quick succession lots of times); requiring the ability to clear the combustion chamber of exhaust gasses in a short space of time before the next intake. It does this by opening the exhaust valve earlier in the latter half of the power stroke and using the end of that explosion to force the exhaust gasses out past the valve quicker, before pushing the remainder out with the piston during the return (exhaust) stroke. By latening (retarding) this valve opening event you are both increasing low down torque as stated above and decreasing the engine's ability to clear the chamber of spent gasses at high rpm, with a resulting loss of top-end power.

The application of this effect is used in Toyota's Dual-VVT engines: https://toyota-club.net/files/faq/16-01 ... al_eng.htm


By moving the exhaust cam back a tooth I basically set the timing in the 1KR to crudely resemble operation mode no.4 of the Dual-VVT table; further increasing torque across the middle of the range at the expense of idle characteristics and high-rpm exhaust gas evacuation.


When tackling hillclimbs I find the standard gearing:engine output is alright til you change into 3rd. Shifting on the limiter at 62mph the engine falls just outside the useable power band and doesn't pick up again til doing 65-70mph, so you end up plateauing around 60 when going uphill, or even slowing down and having to drop back to 2nd depending on the gradient. Obviously for competing in hillclimbs this isn't ideal but the venues I've competed at don't allow you to gather much more speed anyway so I found it preferable just to buzz the limiter in 2nd til the braking point for the next corner.

By retarding the exhaust cam a tooth and increasing the mid-range torque I managed to overcome this problem - the car is a lot pokier on the throttle and acceleration out of low-speed corners is better; I'm hitting 3rd gear a lot sooner on particular sections when climbing my local road and the car continues to accelerate in 3rd gear when I do reach it. The trade-off is that I'm now robbing the top end of power which you notice in 3rd gear approaching 90mph - the car plateaus here instead and there's no obvious point at which to change into 4th; finding the limiter seems to be slower than shifting early but shifting early you haven't got enough low down torque even with the improvement to really move the long gears. It'll still do 105mph with a bit of a tail wind but it's not so keen at the higher rpm's.

With all this said; as you gradually retard the exhaust timing it will improve things to a point then once that point has been passed the potential to generate torque will fall off steeply. I feel that peak performance point has already been passed with -20 degrees of exhaust timing - and that's not to mention having to drive through town in 2nd gear because the car will kangaroo in 3rd at anything below 32mph & stall below 1200rpm. I think there's potentially a much larger gain to be found somewhere between the teeth, one that both increases the torque across the range and still allows the engine to breathe reasonably well at high rpm given the airflow improvements I've made to the exhaust & cylinder head.


So...


Application:


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The sprocket bolts to the cam. It has a slot which corresponds to a dowel on the camshaft - this aligns the sprocket with the cam, setting the timing at the manufacturer-specified interval.
The slot (therefore the dowel) aligns with the tip of the tooth and there are 10 degrees between teeth (20 degs of timing).
To find the middle ground between the standard timing and the -20 degrees I've tried already I need this dowel to line up with the centre point of the dip between the teeth.


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What I've done is milled the locating slot in the sprocket slightly to allow me to rotate the cam 5 degrees counter-clockwise.
This was achieved by removing exactly 1mm of material as shown.
The locating dowel forms a 24mm PCD on the sprocket with a circumference of 75mm; so 1mm of this circumference accounts for ~5 degrees of the circle.


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There's a caveat to doing this which takes the form of the play that I'm adding between sprocket & cam. This play is what's allowing me the 5 degrees of adjustment but the problem would arise if that potential for movement allows the sprocket to slip under load..

My thoughts on this are; the locating dowel obviously locates the sprocket to give the correct timing and will prevent the sprocket turning on the cam, however given the dowel's size and how little it actually pertrudes into the slot in the sprocket I don't believe it's load-bearing. By this I mean the sprocket stays in place due to the pressure applied by the retaining bolt and not because that dowel is there. This is at least what I'm telling myself to justify the notion that even by widening the slot as I have the cam isn't going to slip under deceleration so long as the sprocket retaining bolt is torqued properly. It's spec'd at 47Nm but I'll be torquing to 55Nm now just to be sure.

So assuming all is well my new timing specs will be:


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The exh valve opening later (closer to bdc) will increase torque across the range and in conjunction with improvements to exhaust port flow, the chamber should still evacuate the gasses at high rpm at least as efficiently as it did as standard, or close to it, so the high-rpm power shouldn't suffer as it did when setting the cam back a whole tooth.

In addition to this, I will still be getting valve overlap at High-RPM which should allow the momentum of the escaping exhaust gasses to help pull a greater amount of fresh intake into the chamber just as the inlet valve is opening and the exhaust valve is closing, a feature commonly seen on longer duration competition cam profiles - This may or may not be effective with the standard manifold but the effect should be improved with a 3-1 tubular manifold if I ever try making one.


In summary;

Throwing the concept of fuel consumption, smooth running and intended application out of the window; you could think of the retarded exhaust timing as like a torquey road/rally setup and the standard timing as a peaky circuit setup. In fact, if I do end up raising the rev limit or even turn my attention to circuit racing; unless this thing suddenly goes like a scalded cat with the modified sprocket I'll likely revert to the standard timing to make more use of the top end.


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That's us caught up with the progress here anyway. Hopefully now I don't have a backlog of material to write I'll feel a bit more inclined to progress with actually putting the thing back together!
..and get out of this damn house I've been stuck in all winter :thumbs:

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PostPosted: Tue Mar 10, 2020 9:55 am 
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I like your theory, skeptical of how it might actually improve any or give any noticeable benefit.

But as always I’m really interested in your work and what the outcome of this may be

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PostPosted: Tue Mar 10, 2020 2:57 pm 
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Cheers man. You are welcome to the skepticism and I will certainly be keeping my own judgement objective.

I can empirically state though that retarding the cam a full tooth completely alters the power band and in use has been a noticeable improvement in the part of the power band in question - I've done considerable mileage & testing with the setup - it's no quicker when considered across the entire band though so it's not like it can suddenly outdrag a bigger engine (you take from the top & add to the middle).

Cam timing is like a tightrope, slipping past the threshold a few degrees makes a big difference, at -10 degs of cam that threshold has been well and truly passed. I'm confident that reigning it back a bit will see a bigger gain.

It also pops and crackles on the overrun 8-)

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PostPosted: Tue Mar 10, 2020 5:45 pm 
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Good stuff, would a remap achieve the same results on standard engine, even if it does good to see a different approach. If you moving the power band to more useable area then I can see benefit of that. I had a fairly standard remap on my Mondeo V6 and even I noticed the everyday in gear shove was noticeably improved as apposed to top end BHP figures that are nice to have but barely useable with day to day driving.


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PostPosted: Tue Mar 10, 2020 7:24 pm 
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"It also pops and crackles on the overrun 8-)"

Love it...
Cant wait for more..

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PostPosted: Tue Mar 10, 2020 11:20 pm 
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Steve107 wrote:
would a remap achieve the same results on standard engine

Sort of but not really.


Remapping is the process of adjusting the fuel table values that determine the air/fuel ratio at a given engine speed under a given load, in conjunction with advancing the ignition timing; to achieve the highest output possible without causing knock.

In other words: It makes the most of what the engine can already physically do.

Quote:
I had a fairly standard remap on my Mondeo V6 and even I noticed the everyday in gear shove was noticeably improved as apposed to top end BHP

The maximum output achievable is limited by the amount of air the engine can physically flow through the head, intake & exhaust etc; so for that reason you might see more of an improvement in the middle of the range on a standard engine than at the top where the airflow causes a restriction.


All other things being equal; remapping a standard engine to optimise the fuelling would make the car faster over it's given power band - you might see an improvement to torque low down in the revs where I'm seeing one here but the power band itself is always going to be determined by the cam timing.
I'm just changing where the engine makes it's power, not how much power it's making.

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PostPosted: Fri Mar 13, 2020 12:21 am 
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Well I just stripped the head down for the last time so I can give it another bath to get rid of any contaminants before the final assembly.

Lost count of how many times I've had the valves in & out now..


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I also got some slightly better Elring stem seals to replace the one's I'd already fitted.

I'm not just being picky here - I actually damaged the first seal from the original FAI gasket set a while ago by trying to tap it home with a socket.
I was expecting it to put up a fight & sit on there snug; it didn't need it & I burst the rubber top open :roll:

I couldn't have a rogue Elring on there with the rest of the FAI's, so it's off with the lot! - The Elrings do look markedly better in design & construction too.

You really don't need much force when fitting these, they're deceptively easy to push on and they wobble about a bit on top of the guide til there's a valve in there.


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For reference: The lighter grey seal with the black spring (right) is for the inlet side. The silver spring on darker grey (left) is the exhaust seal.

That'll do for today. It's pretty late and I still need to check for anything I've missed before it gets deep cleaned.

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PostPosted: Tue Mar 24, 2020 6:36 am 
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The Unexpectedly Arduous Process of Pre-build Inspection & The Altogether Relevant Idea that Destruction Presents an Opportunity for New Creation...




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This is the kind of stuff I was looking for: Remnants of the old oil seals hidden behind the lip of the valve guide.


This is what being a dumbass looks like:



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I'd managed to catch the edge of the camshaft journal slightly with the valve tool.

Obviously I was a few beers into the job when this happened as it wasn't the only victim.

It's easily done.


If I ignored a problem like this and assembled the engine anyway, the camshafts would be way too tight - turning the engine over could destroy the journal & bearing surface sending metal around the oil system, possibly even locking up the engine and bending a rod or something catastrophic.

At the very least it will add friction and score the bearing, leading to excessive wear and premature failure.


In hindsight I'm glad this damage happened because it effected a repair that brought with it a huge improvement...


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First I chamfered all the journal edges carefully with 220 grit paper to remove the damage - making sure to sand away from the polished face so as not to pull the material up into a ridge.
We're talking thousandths with the tolerances here so even the sanding direction is important.

A thorough cleaning and a test fit of the camshafts revealed the inlet side was turning ok but the exhaust was still a little tight, so I went back for a second round of 220 then finished up with wet 400 grit.


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(The camera does a good job of making cosmetic surface scratches appear far worse than they are)

I also gave the caps a wet 400 grit chamfer to be sure there was nothing to catch -
The bores are all cut and polished into the casting on a single axis leaving sharp edges, rounding them off slightly is the extra touch that'll prevent added friction if any have taken a knock.

Think of it like skiing on planed flat planks vs. skis with the slightly upturned leading edge..


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You gotta wax those skis if you wanna go fast dude - so whilst I was at it I gave the main no.1 & 2 journals a polish as they were looking pretty scuffed.

Hand polishing with Autosol is never going to achieve the same frictionless micropolished finish that gets done at the factory, so if the journals weren't already particularly dull or scratched I'd be leaving them well alone.


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A second test fit showed improvement - the inlet cam turned well but the exhaust was still tighter than ideal and there was friction just about audible.

A pretty novel approach - In an attempt to trace the cause of the problem I put an extension bar against each cap and listened to the end of it like a stethoscope.. It actually worked, the sound was coming from no's. 3 & 4.

Removing the caps revealed dirty oil from the abrasion and there was slight marking in the cap corners.


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This is where you kind of have to look at the evidence and trust what it's telling you. The journals looked fine to my eyes but the cam obviously wasn't happy in there so I went back again with the 400 grit on the edges that saw an accumulation of dirty oil.

I was only going to polish the no. 1 & 2 journals but after some contemplation I decided to do the lot, including the caps..

Man I am glad I did! It's taken considerable effort but the results are sweet.


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Turning the cam now it's like butter. Better than that even.
Just super smooth and effortless, there is absolutely no resistance to movement except the drag from the assembly lube

- That's a huge improvement to how it was even before I battered the journals.


Hand polishing with metal polish will remove measurably no material - you'd have to be there a long time to really mess up the bore shape - but it does a great job of taking the tops off peaks at a microscopic level and that makes all the difference to bearing performance.

This is probably the most worthwhile bit of polishing I've done to the engine.


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Anyway with that done,

This is also what being a dumbass looks like:


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This happened overnight. Rusty valve guides are not what you want - caused by overspray from cleaning the journals.

Fortunately some genius invented cotton buds & the guides cleaned up with a swab of WD40 but I might not have been so lucky if it'd sat there a few days.

It's important to oil any machined surfaces as soon as they've been cleaned or seen any degreaser - especially ferrous metals.
The same thing happened to the tappets within 30 mins of using the engine degreaser and rinsing them - as well as corrosion to the skimmed faces of the aluminium casting.

I've had to polish the tappet bores for the same reason, though they'd obviously seen some surface wear too.


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It's interesting to consider how much mileage it would actually be possible to get from one of these engines... I've heard people refer to them as 'throwaway' when talking about the feasibility of an engine rebuild;
it isn't a term I particularly like on account of the wastefulness but I think what it refers to is the engine being soft cast aluminium with steel running gear & no bearing inserts;
naturally the wear is going to occur to the head casting itself so once it reaches it's serviceable limit the entire cylinder head needs replacing.

The wear caused by the camshaft is mostly a product of timing chain tension, appearing on the bottom insides of the timing-end no.1 & 2 journals and on the no.3 & 4 caps.
The oil clearance for the bearings has roughly .04mm of margin, I'll assume they began life at the tighter end of that margin: Although there is wear present after 120k miles (visible by the banding left from the oil cutouts in the camshaft) it doesn't look anywhere close to the .04mm serviceable limit.


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The weakest link however is the bottom of the tappet bores, as the tappets see lateral loading from the rotating cam lobes whilst being pushed down -
There's a palpable indentation in the wall here & this is likely why these engines begin to make the characteristic cold-start tapping noise as the mileage creeps up...

This sound is something I see questioned a lot on the forum - It's not really an issue.
It would take a considerable amount of wear for the tappets to stick in the bores & they'd become obnoxiously loud before that happened.

Fixing the tapping noise would require replacing the cylinder head but a thicker oil will help to quiet it down.


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The camshaft and tappets themselves are made of a much harder material than the head casting they interface with, so they don't see much wear under normal circumstances - good news if you're looking to source these parts second hand.


Inspecting these areas after 120k miles of hard use with good maintenance I would hazard a guess that things here will start to get a bit sloppy around 200k miles but (assuming the bottom end is up to it) I imagine the engine will still operate beyond that given the work I'm doing here. I'll keep an ear on those tappets for the next 80k and see how that develops.

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PostPosted: Tue Mar 24, 2020 10:50 pm 
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Nice one Bunkey, What Engine oil are you going to use in this rocket ?

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PostPosted: Wed Mar 25, 2020 7:48 pm 
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SlackGarry wrote:
Nice one Bunkey, What Engine oil are you going to use in this rocket ?


Haha. I'll be sticking with the 5w-40 C3 oil I've been using for a while.

I'm going to run the engine in using 5w-30 for the first few hundred miles though to make sure it easily flows through all the nooks and crannies where its supposed to be and flushes everything out.
Then I'll do an early filter change and switch back to the 5w-40.

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