Camshaft replacement/swap: Does the engine need to be dropped?

[Fit]

Hi guys!

I am currently considering changing my cams to aftermarket cams.
However I would like to find out from members who have worked in replacing or tearing apart their engines if I need to drop the whole engine out in order to replace the cams?

Can it be done with the engine still in the car and just removing the cylinder head cover?

Thanks in advance.

[inuvik]

Hi guys!

I am currently considering changing my cams to aftermarket cams.
However I would like to find out from members who have worked in replacing or tearing apart their engines if I need to drop the whole engine out in order to replace the cams?

Can it be done with the engine still in the car and just removing the cylinder head cover?

Thanks in advance.

You do not need to remove the engine but is the new cam MIVEC compliant?

Variable valve control systems optimize power and torque by varying valve opening times and/or duration. Some of these valve control systems optimize performance at low and mid-range engine speeds, while others focus on enhancing only high-rpm power. The MIVEC system provides both of these benefits by controlling valve timing and lift. The basic operation of the MIVEC system is altering the cam profiles and thus tailoring engine performance in response to driver input.[8]
In essence, MIVEC serves the same function as "swapping cams", something that car racers might do when modifying older-design engines to produce more power. However, such swaps come with a compromise - generally yielding either greater low-end torque or more high-end horsepower, but not both. MIVEC achieves both goals. With MIVEC, the "cam swap" occurs automatically at a fixed engine speed. The Cam Switch operation is transparent to the driver, who is simply rewarded with a smooth flow of power.[8]
Two distinct cam profiles are used to provide two engine modes: a low-speed mode, consisting of low-lift cam profiles; and a high-speed mode. The low-lift cams and rocker arms - which drive separate intake valves - are positioned on either side of a centrally located high-lift cam. Each of the intake valves is operated by a low-lift cam and rocker arm, while placing a T-lever between them allows the valves to follow the action of the high-lift cam.[8]
At low speeds, The T-lever's wing section floats freely, enabling the low-lift cams to operate the valves. The intake rocker arms contain internal pistons, which are retained by springs in a lowered position while the engine speed is below the MIVEC switchover point, to avoid contacting the high-lift T-shaped levers. At high speeds, hydraulic pressure elevates the hydraulic pistons, causing the T-lever to push against the rocker arm, which in turn makes the high-lift cam operate the valves.[8]
MIVEC switches to the higher cam profile as engine speed increases, and drops back to the lower cam profile as engine speed decreases. The reduced valve overlap in low-speed mode provides stable idling, while accelerated timing of the intake valve's closing reduces backflow to improve volumetric efficiency, which helps increase engine output as well as reduce lift friction. High-speed mode takes advantage of the pulsating intake effect created by the mode's high lift and retarded timing of intake valve closure. The resulting reduced pumping loss of the larger valve overlap yields higher power output and a reduction in friction. The low- and high-speed modes overlap for a brief period, boosting torque.[8]
From the 4B1 engine family onward, MIVEC has evolved into a continuous variable valve timing (CVVT) system (dual VVT on intake and exhaust valves).[9] Many older implementations only vary the valve timing (the amount of time per engine revolution that the intake port is open) and not the lift. Timing is continuously independently controlled to provide four optimized engine-operating modes:[9]

• Under most conditions, to ensure highest fuel efficiency, valve overlap is increased to reduce pumping losses. The exhaust valve opening timing is retarded for higher expansion ratio, enhancing fuel economy.
• When maximum power is demanded (high engine speed and load), intake valve closing timing is retarded to synchronize the intake air pulsations for larger air volume.
• Under low-speed, high load, MIVEC ensures optimal torque delivery with the intake valve closing timing advanced to ensure sufficient air volume. At the same time, the exhaust valve opening timing is retarded to provide a higher expansion ratio and improved efficiency.
• At idle, valve overlap is eliminated to stabilize combustion.

[Fit]

Yes it is mivec compliant.

[Qrush]

Here's the Engine Overhaul/Camshaft Removal DIY, from the 2015 Mitsubishi Mirage Service Manual:
















Here's a link to some vids of M's Racing Development, installing cams on the 3A92 engine:
https://m.facebook.com/pg/Msracingca...ernal&mt_nav=0

Hope this helps.

[Fit]

That’s nice info! I didn’t know they had a video as I don’t have Facebook.

[Loren]

I didn't spend enough time looking at this, and I didn't take any significant photos. But, we did a 20-minute autopsy on my over-revved engine a while back. To get the cams out, you have to remove the timing chain. To remove the timing chain, you have to remove the front timing cover. And I'm pretty sure we learned that you have to remove, or at least loosen the oil pan to remove that cover. We just took things far enough apart to pull the chain and ultimately remove the head for inspection. (bent exhaust valves, all of them) To get everything properly sealed upon reassembly, I'm pretty sure you'd want to drop the oil pan completely. But, again, didn't look at it that closely. Just removed enough bolts to yank it apart and get the head off of the block with no intention of it ever running again. It was returned as a core.

You can probably replace the cams in the car, but it's really not difficult to pull the engine. 30 minutes has the front bumper, core support and radiator out. Lower dog-bone mount, two upper mounts... plus the usual hoses, wires and cables.

I would raise a really big question about valve springs, though. The stock valve springs are barely sufficient to do their job. They are designed to produce no more friction than absolutely necessary. You can compress these valve springs by hand, they are VERY soft.

I'm no expert on cams and valve springs, but I think upgrading the cam would be wise to include stiffer valve springs. Might get away with it as long as you keep the stock rev limit. Going beyond that, though... DEFINITELY stiffer valve springs.

[inuvik]

I would raise a really big question about valve springs, though. The stock valve springs are barely sufficient to do their job. They are designed to produce no more friction than absolutely necessary. You can compress these valve springs by hand, they are VERY soft.

I'm no expert on cams and valve springs, but I think upgrading the cam would be wise to include stiffer valve springs. Might get away with it as long as you keep the stock rev limit. Going beyond that, though... DEFINITELY stiffer valve springs.

I thought of this also after reading about your tear down after over revving. Since the 3A92 and 4A92 are the same motor with just 1 less cylinder I can't help but wonder if the 4A92 valve springs are stiffer.

[Loren]

The 4A92 is just a 3A with an extra cylinder. I would expect the valve springs and every individual cylinder-related part (piston, connecting rod, bearings, valves, valve springs, lifters, etc) to be exactly the same. That's the whole point of an engine family: share parts and reduce the number of parts in inventory.

There would be no need for the 4A to have stiffer valve springs unless it has more valve lift, or revs higher.

[inuvik]

The 4A92 is just a 3A with an extra cylinder. I would expect the valve springs and every individual cylinder-related part (piston, connecting rod, bearings, valves, valve springs, lifters, etc) to be exactly the same. That's the whole point of an engine family: share parts and reduce the number of parts in inventory.

There would be no need for the 4A to have stiffer valve springs unless it has more valve lift, or revs higher.

I'm not sure whether the 3A92 has softer valve springs to maximize efficiency? The 4A92 has a listed compression ratio of 11:1 where the North American 3A92 compression ration is 10.5:1. In some markets the 3A92 has 11:1 compression (same as the 4A92). The 4A91 is listed as having 10.5:1 compression. So for North America at least it appears the 3A92 is using the 4A91 pistons and in some markets the 3A92 uses the same pistons as the 4A92?

[Loren]

There are a lot of little things they could do to account for a half point difference in compression. Bore and stroke are the obvious, but even if those are the same, a slight change in piston top design, difference in head gasket thickness, combustion chamber shape, etc.

Wouldn't be too hard to look up part numbers if you really wanted to know which parts are the same. But, we're straying from the topic at hand.