2.4 Piston Durability

[MT-2.4]

I have read in several posts that the stock 2.4 Omega engines use cast pistons which are fragile and should be limited to about 6000 RPM's and that this is a problem will all of the pistons fitted to the various 2.4 engines.

“be careful with the std 2.4 pistons they are quite fragile,
don't go beyond CR9.5 & 6000rpm,
if you plan to improve your head flow then forged pistons are advised.
HTH,
Hiro”

“The 2.4 pistons are supposedly weak for high rpm use or boost. But I am wondering if this is true for all 2.4l engines. I've found information that indicate not all years had the same pistons and that some of the years were stronger than others.
they are all weak above 6000rpm & about CR9.5
I think linear speed is bordeline for a cast piston because of increased stroke
(6500rpmx85mm = 18.4m/s)
this problem in enhanced by of the bad rod ratio (1.57) that puts huge lateral load on the piston & bore.
Hiro”

However when reading the description of the 2.4 engines for sale by OGTS they clearly say that they are “a very special Opel performance engine” fitted with “Opel's most wanted forged steel crankshaft, special heavy duty rods and forged pistons”.

So is this description some sort of typo, or is OGTS actually selling a performance engine? And do you guys think the forged pistons in those motors should be limited to 6000 RPM redline as the standard cast units?

[Gumby]

The 2.4 motor isn't really a high reving motor to begin with. I can't speak from experience on what OGTS is selling but you might try just giving them a call to see if they are replacing the pistons with aftermarket parts. My last discussion with them leads me to believe they are not replacing the pistons since they no longer stock forged aftermarket pistons for the 2.4 engine. If you had them rebuilt a 2.4 motor for you I am sure you could specify that you wanted forged pistons.

[jeff denton]

I'm not real "up" on details about the 2.4 specifically, lately I'm trying to learn all I can about a certain 2.2 part...
But I would take the catalog's wording as gospel, you can count on dealing with very honorable people at OGTS. By all means call them and ask questions. You can learn a lot in a minute on the phone with Gil.

[wrench459]

Your right about the piston speeds. With a cast piston you're going to grenade the motor anything over 6 grand.
What are you after anyway? Low rpm torque which the 2.4 is good for, or a high H/P motor?
I'm not saying you can't make a 2.4 twist and turn but it will take some high end parts to keep it alive.
Better yet lets make a torquer with some serious H/P all in one package.
Pay close attention to what Hiro has to say. My two cents for what ever its worth.

[lamchop77]

I'm in the process of building a 2.5 motor and have pulled apart 2 of the 2.4 engines fitted to the Frontera in the UK. These i'm led to believe have forged steel crank/rods as standard (Hiro will probably enlighten us to any differences in the build of these from the factory).

The pistons that are fitted are MAHLE and are cast pistons which are dished slightly. Both the 2.4's i've taken apart have scuffed piston skirts and the top 5-10mm of the bores have a huge step. All the forums i've been on come up with the same problems for the 2.4 which are bore wear and piston scuffing!!. The good thing is that uprated parts are fairly easily available for the 2.4 in europe (pistons, rods, light flywheels,etc)

I'll see if i can get a part no off the piston so you can check it against the pistons on the motor your looking at.

HTH

Chris

[First opel 1981]

Hey, I will admit to not knowing Jack Schmidt about the 2.4s but I have to ask if it has cylinder oilers? The little squirters from the sides of the rods.
I was just enlightened to their existance a week or so ago and can't help but wonder if that is a weak point in the engine design.

[Hiro]

Hi to all,
So here is a summary of what I've seen with the 2.4/2.5 CIH:

My first race 2.4 CIH was a near-stock one:
Std crank + rods + pistons,
Balanced short block
CR was 8.8
Mild ported 2.4 head with a small cam (276° @ 0.3mm)
This version revved nicely upto 6000rpm without problem,
I've raced it during a year or so.

First upgrade of this near-stock 2.4 included:
CR 9.8
Better ported 2.2 head with slightly bigger cam (294° @ 0.3mm)
Bob's roller rockers.
This version revved very nicely upto 7000rpm,
But after 2-3 races I had ring land failure on 3 cast pistons.

Second upgrade goes this way:
Wossner forged pistons (96mm bore)
CR is now 11
Same ported 2.2 head with bigger cam (310° @ 0.3mm)
Bob's roller rockers.
This version spins upto 8000rpm in spite of its bad rod ratio (1.57)
No failure after one year of racing.

In paralelle to this second upgrade I've built another similar engine this way:
Wossner forged pistons (97mm)
Much lighter short block with better balancing
CR 11.3
Same head as above with Bob's roller rockers.
This one takes 8500rpm like a blitz,
No failure to report yet,
This year I will set the rev limiter to 8000rpm for added safety
(the FW is still a cast reworked one).

So my end conclusion about the 2.4/2.5 are:
very good steel crank
very good steel rods
fragile cast pistons above CR9 & 6000rpm
crappy rod ratio results in fast bore wear @ high rpm
good head for further porting jobs.

A budget 2.4 with std pistons is very nice if you stick to my first version,
But don't go to the first/second & third upgrades without forged pistons!
HTH,
Hiro

[lamchop77]

Hiro

Did you re-use the std 2.4 rod bolts on the first couple of engines or did you get new ones? Do you have the part numbers of these?

Also i want to use the std rods for the 2.3 motor as it is a stop gap engine until i can afford to properly finish the 2.5. Looked at the pictures the rods you prepped up and it looks like you have polished all over. Where is it best to remove material from safely and how did you do it( die grinder, emery cloth, wet n dry, etc). i have got access to calibrated accurate scales but should is there anything else i should do other than weight match?

Thanks

Chris

[jeff denton]

Nice report, Hiro!
So he's saying that the 2.4 shouldn't be over-revved unless the quality of the piston is improved. Not unusual, huh?
So when going to the trouble of improving the piston a guy might as well go the next couple steps here and get the rod length improved. Which can bring the weight of the piston way down (pin height is higher so skirts can be less).

[lamchop77]

Jeff

Yeah you can do that, got a quote from Mike at R & R Racing products to do it, $933 for a set of 4, forged steel items with ARP rod bolts, 12 weeks to make them. Just a bit too expensive at the moment!!!!! I think i would be interested if the price could be brought down a bit.

Anyway you should be thinking about 2.2 stuff shouldn't you!?!?

HTH

Chris

[RallyBob]

Originally Posted by MT-2.4 However when reading the description of the 2.4 engines for sale by OGTS they clearly say that they are “a very special Opel performance engine” fitted with “Opel's most wanted forged steel crankshaft, special heavy duty rods and forged pistons”. So is this description some sort of typo, or is OGTS actually selling a performance engine? And do you guys think the forged pistons in those motors should be limited to 6000 RPM redline as the standard cast units?

I really don't like to undermine OGTS if I can help it, as they are very knowledgable about what they do, as well I know the owner and employees fairly well.

However, the 2.4 CIH engine (normal production CIH, not the Cosworth-developed DOHC engine) has cast pistons, not forged.

As far as whether or not the engine *should* be revved above 6000 rpms, keep this in mind: The engine's peak power occurs at 4800 rpms. By 6000 rpms the power has fallen drastically (IIRC it's almost 40% below peak). Why would you want to rev it that high? You will in fact only accomplish two things: You'll actually go slower, and you'll increase wear of the engine at an exponential rate.

Now, if you have the appropriate supporting mods, such as a VERY big camshaft, multiple sidedraft carbs and/or larger EFI system, larger valves and head porting, etc....then you can make power at 6000+ rpms. But if you are going that route you need higher compression to compliment the bigger cam anyway, so you need aftermarket (forged) pistons.

Bob

[RallyBob]

Originally Posted by First opel 1981 Hey, I will admit to not knowing Jack Schmidt about the 2.4s but I have to ask if it has cylinder oilers? The little squirters from the sides of the rods. I was just enlightened to their existance a week or so ago and can't help but wonder if that is a weak point in the engine design.

Word is that some DO, and some DON'T. I have personally only seen them with oil squirters over the past 14 years of my dealing with 2.4's, however Hiro assured me some time ago he has seen some engines without them.

[Hiro]

Originally Posted by lamchop77 Hiro Did you re-use the std 2.4 rod bolts on the first couple of engines or did you get new ones? Do you have the part numbers of these? Also i want to use the std rods for the 2.3 motor as it is a stop gap engine until i can afford to properly finish the 2.5. Looked at the pictures the rods you prepped up and it looks like you have polished all over. Where is it best to remove material from safely and how did you do it( die grinder, emery cloth, wet n dry, etc). i have got access to calibrated accurate scales but should is there anything else i should do other than weight match? Thanks Chris

I have new 2.4 rod bolts from Risse Motorsport.
The rod beams are worked with a big rotative stone (I don't know how this tool is called in english...),
The rest of the rod is deburred with my airdye grinder & carbide tips or small diameter rotative stones,
No real polishing but a fast work with abrasive paper & oil.
I try to remove material evenly on all sides of the rod,
Also removing sharp edges/cast marks etc that could cause failure.
For the 2.4 rods I didn't weight-match the big ends/small ends,
But at least all the caps were the same weight & the rod bodies also,
So I hope there is no major big end/small end off-balance.
For my 2.7 rods I had to look to the big end/small end weights,
Because apparently one of the rods came from a different set.
Hiro

[Hiro]

Originally Posted by jeff denton Nice report, Hiro! So he's saying that the 2.4 shouldn't be over-revved unless the quality of the piston is improved. Not unusual, huh? So when going to the trouble of improving the piston a guy might as well go the next couple steps here and get the rod length improved. Which can bring the weight of the piston way down (pin height is higher so skirts can be less).

Yes Jeff there is room for improvement with the 2.4/2.5 CIH,
But as the std piston cd is already 31.5mm we very fast bump into the piston design issue...
Still possible to get a 1.63 rod ratio but that's probably the upper limit with the CIH block height.
Hiro

[Hiro]

Originally Posted by RallyBob Word is that some DO, and some DON'T. I have personally only seen them with oil squirters over the past 14 years of my dealing with 2.4's, however Hiro assured me some time ago he has seen some engines without them.

In fact the "without hole" 2.4 rod is shared with the 24V 3.0 6 cylinder CIH.
Now racers have different opinions about this:
Some racers prefer the "without hole" rod because they say it is less prone to failure @ high rpm,
Others argue that this oiling hole is usefull to reduce bore wear,
Because the CIH piston takes the combustion pressure asymetrically during the power stroke.
I don't know how far all this is true,
Uptill know I've been using 2.4 rods "with holes" (already present or post-drilled in the body).
Among 6 sets of 2.4 rods I have 4 sets "with hole",
Apparently the "without hole" 2.4 rod is more frequent in German 2.4 engines.
Cheers,
Hiro

[DennisGardiner]

I think the issue/s are honestly revolving around street engines verses racing engines.

'Hiro' is definitely responding to the racing aspect.

Race engines, (that regularly see 6000+ rpm),... yes, you will want to install forged pistons. That rule of thumb applies to any race engine or 'boosted' engine.

Even Hypereutectic pistons will not withstand 6000+ rpms for a very long time.

Street engines, (especially old-school engines, such as the Opel CIH family of engines), have a Opel specified factory upper red-line limit of 5800 rpm with 6200 rpm (as opel calls it) a 'burst limit'.

Personally, (owning and driving my 2.4L for over 19 years) I have to say the stock 2.4L pistons have been just fine.

I have read on these forums before that quote, 'the 2.4L pistons are 'very fragile'.

I personally think this is too harsh of an assessment for a "Stock" engine, naturally aspirated. (Ie. not boosted {turbo or super charger})

I have owned my 2.4L since 1990 and have put many miles on the engine since. I have revved the engine to 6000 rpm before, and have run her up to 131 mph on numerous occasions. {Opelwasp beware, you may write me a ticket.}

I think it would be better to state, "2.4L pistons are not suited for racing use", and that for racing-use the pistons should be replaced for forged units.

Dennis

[MT-2.4]

Wow what good information.
I wanted to let everyone know that I didn’t mean to question OGTS or the veracity of their descriptions, I have always had really good experiences dealing with Gill and I certainly couldn’t have done the conversion with out all of his help.
As for the redline question, I don’t intend to exceed 6000 as this is an unmodified 2.4 street motor that I bought mainly for the torque, I have just always been confused by the discrepancy. Plus it’s nice to know exactly what is in the motor, just for piece of mind.

[Gumby]

Originally Posted by MT-2.4 Wow what good information. I wanted to let everyone know that I didn’t mean to question OGTS or the veracity of their descriptions, I have always had really good experiences dealing with Gill and I certainly couldn’t have done the conversion with out all of his help. As for the redline question, I don’t intend to exceed 6000 as this is an unmodified 2.4 street motor that I bought mainly for the torque, I have just always been confused by the discrepancy. Plus it’s nice to know exactly what is in the motor, just for piece of mind.

For a low reving street engine you should be more than fine. Even in a built engine I wouldn't want to rev the thing (bad ratios). My goal was to go no farther than 6k with forged pistons anyway. I think high RPM peak HP in a street engine is for most purposes useless since under most circumstances you'll never tap into that power. The HP the engine makes between 2k - 4.5k has always been the most important to me personally since that is where I'd use it most (gives the feeling that the car has a real strong motor compared to something that has to be spun up to make power). I have a buddy with a dodge that has a modified cummins turbo diesel that has spanked more than a few Honda's when he prespools the turbo up to about 30lbs of boost at a red light. It's an automatic too O_o that will set you back in the seat nicely off the line simply because of the huge amount of torque it produces in just about its entire RPM range.

Do you already have a 2.4 or are you planning on getting one from OGTS? My recommendation if you go the OGTS route would be to have them rebuild it simply because they'll know the engine far better than any engine builder or machinist is likely to know it. If you are looking for just a used engine procuring one from Germany will be cheaper than buying from OGTS (by a lot) BUT it does come with potential headaches from the department of homeland security (asking me how I know :/). So that is just a matter of whether you have the money or you want to deal with the potential holdups of importing engine parts.

Best of luck with your 2.4!
-Levi

[Hiro]

Originally Posted by DennisGardiner I think the issue/s are honestly revolving around street engines verses racing engines. 'Hiro' is definitely responding to the racing aspect. Race engines, (that regularly see 6000+ rpm),... yes, you will want to install forged pistons. That rule of thumb applies to any race engine or 'boosted' engine. Even Hypereutectic pistons will not withstand 6000+ rpms for a very long time. Street engines, (especially old-school engines, such as the Opel CIH family of engines), have a Opel specified factory upper red-line limit of 5800 rpm with 6200 rpm (as opel calls it) a 'burst limit'. Personally, (owning and driving my 2.4L for over 19 years) I have to say the stock 2.4L pistons have been just fine. I have read on these forums before that quote, 'the 2.4L pistons are 'very fragile'. I personally think this is too harsh of an assessment for a "Stock" engine, naturally aspirated. (Ie. not boosted {turbo or super charger}) I have owned my 2.4L since 1990 and have put many miles on the engine since. I have revved the engine to 6000 rpm before, and have run her up to 131 mph on numerous occasions. {Opelwasp beware, you may write me a ticket.} I think it would be better to state, "2.4L pistons are not suited for racing use", and that for racing-use the pistons should be replaced for forged units. Dennis

Dennis I basically agree with you.
The only important thing to remember with the std 2.4 piston is to stay as close as possible to the stock setup,
Including CR & rpm redline.
As Bob said the 2.4 peak power is only @ 4800rpm so there is no need to rev it beyond.
For pure race use there is no question: forged pistons are mandatory,
Now what about a mildly tuned street 2.4?

IMO the safety margin of the std 2.4 piston is relatively small,
This is quite different from the 1.9/2.0/2.2 where std cast pistons can cope with a broader rpm & CR increase.
This is what I mean by "the std 2.4 pistons are very fragile",
Because IMO they can't be used as safely as the 1.9/2.0/2.2 pistons in a mildly tuned street CIH,
I think this deserves a special "caution note" just to be on the safe side.
Hiro

[hrcollinsjr]

Originally Posted by Hiro IMO the safety margin of the std 2.4 piston is relatively small, This is quite different from the 1.9/2.0/2.2 where std cast pistons can cope with a broader rpm & CR increase. This is what I mean by "the std 2.4 pistons are very fragile", Because IMO they can't be used as safely as the 1.9/2.0/2.2 pistons in a mildly tuned street CIH, I think this deserves a special "caution note" just to be on the safe side. Hiro

Basically you're saying the 2.4 std. cast piston is up to the task of a stock application, which makes sense on a production engine, but not much beyond that. Whereas the 1.9/2.0/2.2 pistons are more than "just"up to the task and can be utilized in higher performance engines. I'm also guessing the quality of pistons is probably the same regardless, that the main difference is the extra stress or load placed on the 2.4 piston because of the rod ratio that keeps being referred to as not the most desirable.

Harold

[Hiro]

Originally Posted by hrcollinsjr Basically you're saying the 2.4 std. cast piston is up to the task of a stock application, which makes sense on a production engine, but not much beyond that. Whereas the 1.9/2.0/2.2 pistons are more than "just"up to the task and can be utilized in higher performance engines. I'm also guessing the quality of pistons is probably the same regardless, that the main difference is the extra stress or load placed on the 2.4 piston because of the rod ratio that keeps being referred to as not the most desirable. Harold

this is my understanding too Harold.
rod ratio & piston speed are the problems with the std 2.4
suggesting the 85mm stroke upgrade was a tad farfetched from the original CIH design.
probably a 80-82mm stroke is better to get both a bigger displacement & a reasonable rod ratio,
we are several CIH builders here to consider this route now,
can be done quite easily by offset grinding a 2.2 crank.
Hiro

[RallyBob]

Originally Posted by hrcollinsjr Basically you're saying the 2.4 std. cast piston is up to the task of a stock application, which makes sense on a production engine, but not much beyond that.

I'd even go as far to say that while they are plenty strong for the stock engine's power and rpm range, they will not tolerate detonation nearly as well as a 1.9/2.0/2.2's pistons can. I think, based on inspection, that it's a fact based on the lightweight piston design, and the crappy rod leverage/rod ratio which puts tremendous side-loadings on the skirts and ring lands. This can be seen by inspecting a higher mileage 2.4, the cylinder bore and piston wear is tremendously higher than it would be if the engine were a 1.9/2.0 litre engine.

If those same 2.4 pistons were used with a longer rod and a shorter stroke, they may in fact prove to be suitably durable for higher rpms and power.

[jeff denton]

I still think a "spacer plate" between the block and head could fix the rod length issue...
Did anybody catch the recent issue of Hot Rod Mag, the guys from Montana who built a 1928 Dodge w/flathead 4-cylinder, didn't get the record at Bonneville but had fun trying. Rods were nine inches long.

[Hiro]

Originally Posted by RallyBob I'd even go as far to say that while they are plenty strong for the stock engine's power and rpm range, they will not tolerate detonation nearly as well as a 1.9/2.0/2.2's pistons can. I think, based on inspection, that it's a fact based on the lightweight piston design, and the crappy rod leverage/rod ratio which puts tremendous side-loadings on the skirts and ring lands. This can be seen by inspecting a higher mileage 2.4, the cylinder bore and piston wear is tremendously higher than it would be if the engine were a 1.9/2.0 litre engine. If those same 2.4 pistons were used with a longer rod and a shorter stroke, they may in fact prove to be suitably durable for higher rpms and power.

I agree Bob,
Hey maybe I will not sell all of my 2.4 cast pistons!
Hiro

[lamchop77]

Originally Posted by Hiro In fact the "without hole" 2.4 rod is shared with the 24V 3.0 6 cylinder CIH. Now racers have different opinions about this: Some racers prefer the "without hole" rod because they say it is less prone to failure @ high rpm, Others argue that this oiling hole is usefull to reduce bore wear, Because the CIH piston takes the combustion pressure asymetrically during the power stroke. I don't know how far all this is true, Uptill know I've been using 2.4 rods "with holes" (already present or post-drilled in the body). Among 6 sets of 2.4 rods I have 4 sets "with hole", Apparently the "without hole" 2.4 rod is more frequent in German 2.4 engines. Cheers, Hiro

Hiro/Bob

Just dug out my 2.4 rods to work on getting them balanced/ shotpeened for the 2.3 motor. I noticed that both sets have no oil squirters in them. Don't know whether to use them as they are or drill the oil ways into them (was just going to copy the 2.2 rods oilway positioning). Do you think i may run into bore wear problems considering that i'm using total seal rings as well?

The rod ratio is 1.729 with 97mm pistons on this engine just to remind you. The engines that the rods/crank i'm using came from the Vauxhall Frontera 4x4 so looks like all these motors have rods without oil squirters.

Cheers

Chris