The temperature isn't very extreme in this application. There are other rubber products that have better mechanical properties. There are 2 part pourable polyurethane rubbers. Belzona 2141 comes to mind.

Chockfast Orange is pourable epoxy grouting compound, that could be applicable here. It costs about $1 per cubic inch.

Those are both really interesting, thank you for the recommendations.

Chockfast Orange has quite a nice thermal expansion rate, and other really nice ratings... I wish I had more blocks to experiment on. I'm surprised I haven't heard of this before.

Thanks again

Silicone rubber elastomers have a much lower modulus than metals. Probably wouldn't offer sufficient support.
Adding chopped carbon fibre or glass fibre to epoxy produces high-modulus, lightweight resins. Popular for 3D printing.

je suis charlie

You are certainly right about the lower modulus. However, my thinking here is that if you use something that has "enough" modulus, but has very high damping, it would do the job "better" by reducing stress build up from differential thermal expansions. Nothing will expand quite like aluminum will, especially won't conduct heat well. I think the aluminum epoxy and pc 9020 is working well because it's basically over expanding that gap, while in it's glass temperature state. So it is sort of squishing and filling the coolant jacket. But I suppose I don't quite know how much the sleeve actually expands in this situation, and how much stress is added by this.

I was looking at some neoprene rubbers that can handle the temperature as well.

It certainly depends on the block design, but these small blocks aren't cracking initially under higher cylinder pressures, they tend to crack after an amount of use at those higher cylinder pressures. Unlike the more open deck blocks of the imports, which start breaking almost immediately at increased cylinder pressures.

Another thought is to run one of these epoxies in that glass transition state (at operating temp), in sort of beams parallel to the bore. Adding passages parallel to the circumference of the sleeve to allow coolant to fully circulate rather than solidly filling the area. But again, how much the sleeve expands, and how much the epoxy squishes is something I'm unsure about. As this could just concentrate stress where the epoxy slows expansion (since it will be effectively trapping the heat), and distort the bore in specific areas...

I do like the idea of adding an aggregate of sorts. Personally though I have been leaning towards aluminum powders rather than carbon fiber for more homogenous thermal properties...

Another idea I have considered is some kind of low temperature solder. The similar thermal expansion rate and conductivity to aluminum of one of these solder mixes is more appealing than epoxy. Some of the solders would be workable just above operating temp, so they shouldn't realistically hurt the heat treat of the casting. And I'm fairly certain this would be cheaper than epoxy as well. Hardest part is having some kind of oven big enough for a block (which is not too hard to figure out).

But that would sort of be a more "support" strategy than damping. Which is sort of why I came here to pick some brains...

I know what I'm asking is overly vague because I haven't put an example into the conversation. Is it mostly just a lack of strength do you think that would cause an aluminum block to crack (when an iron block of the same design doesn't)? Or could it actually be more about the damping and fatigue strength?

I can only make a few observations, I don't have knowledge here.

Block fill is at the bottom of the bore where the cylinder is not exposed to firing pressures.

Steel sleeves and cast iron bores in diesel engines experience cavitation on the coolant side in the middle portion of the cylinder due to extreme vibration. I don't know if this is caused by the firing pressures or other dynamics of the piston in the cylinder. Perhaps aluminum engines aren't as tolerant of the high stress from vibration?

Diesel engines with wet liners retain the liner at the top, The bottom of the liner sits in o-rings s is free to move like a piston in the lower cylinder entablature. There is clearance between the liner and block with o-rings to seal it up.

Most epoxies shrink when they cure. Grouting epoxies such as chockfast are uniquely low shrinkage. If you need your epoxy to expand to help retain the liner perhaps you should be looking for an epoxy that won't leave a gap after it cures.

Wet liner gas engines in the 60s used the same architecture.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

Very interesting to hear about the cavitation in diesels in the coolant area. Never heard about that. I feel these vibrations in cast aluminum are what kill the block. Likely just seek out stress in the casting... As HIP is a very popular and quite a successful treatment for aluminum blocks...

Makes me wonder about deep cryo treatment of aluminum blocks. Obviously this would have to be done without the iron sleeves.

My block when re-sleeved had interference fit steps added, but is mostly retained with a sleeve retainer (620 etc).


Chockfast Orange seems to be the best product overall... Linear thermal expansion is most similar to aluminum. I'll look for a good price on it.

Which direction do the cracks run, longitudinally or circumferentially? Longitudinal cracks I would suspect to be pressure related, circumferential cracks may be temperature related.

They are all longitudinal. They all also happen intermediate of the structural support to the block deck, at the top of the sleeve.

Not my pictures but this is what we are talking about. Almost all of the ones I have seen (online or in person), the crack is at the top of the sleeve, just inside the support. To me, it looks like the vibration builds up stress there, more than anything. The lack of "support" just abuses the modulus of the material and it cracks I believe.

Next the two casting materials should be the same; 319 t5

The second pic is what's really interesting; the crack has broken the aluminum casting but not the spun cast iron, yet. Which to me is even more evidence that this is a vibrational issue.

My follow up...
I ended up going with pc 9020. I feel this is actually the better solution over chock fast orange. It reaches the glass transition temperature much sooner (38c vs 60c), so it will act much like what I was describing earlier. With some relief holes in place, I am not worried at all with higher CTE than the block material. It will effectively begin to rubberize at about 100* F.

The other product I came very close to buying was PC 9416. It has a 15 cte under TG, and then 40 over. But the TG point is much higher at 63c. So with the CTE being under that of the aluminum, and being at rather warm operating temperature, I felt it would be more detrimental to the bore expansion. Also, I found pc 9020 for cheaper than the floor repair option.

Chockfast Orange still is worth considering. However, there is no data on the TG point... Which I assume is 60c just judging by the TDS. More importantly, I don't know what the CTE is at that point...

I estimate that the 38c TG point will end up causing the least amount of stress on the aluminum portion of the sleeve. Thus making a more durable block. I know this has been a popular product for this application, and it finally clicked as to why.

There are other solutions that will work here, I know this. But this is my train of thought, and is not reflective of the previous use of such a compound, but of my understanding of this problem at hand.

Hopefully this information will be useful to someone in the future.