rmdhawaii

iTrader: (4)

The last time I ran this engine, it ran just fine. No problem tuning it. Lots of power. When I opened it up today, I see this mean gouge down the side of the piston and I'm like, "What's up with this?"

What are you thoughts on this and how did it get this way? Why is it still running okay? What could happen if I continue to run it?

I'm assuming I can't continue running it like this ... or can I?

Roelof

Something did go through the engine?
A plugwire or a pistonpin clip?
Or else check the bearings.

The piston is damaged but there is nothing to loose to build up the engine and give it a try, I have seen this before after a plugwire and the engine did run fine afterwards.

CurveTracer

iTrader: (5)

The top of the piston looks pretty pitted. Does the surface of the head button look pitted also? I would think that the pitted surfaces would have a negative effect on combustion efficiency.

Hey Roelof, how much engine performance do you estimate will be lost due to the piston and or head button pitting?

brc358

iTrader: (18)

You should just change out the piston,rod and sleeve.
Once the engine warms up and there is expansion in the sleeve, you will loose a lot of compression.
I have tried to get by during races with pitted piston and sleeves, and even sanded the top of the pitson with 1500 wet/dry sand paper to remove some of the pitting, but I barely made it through the day. Plus you have the deep gouge in the side of the piston which will lose even more compression.
Looks like you made have lost the snap ring for the wrist pin.

Roelof

It is depending the status of the P/S set, if it stil had some pinch it could hold up just fine.

Indeed use some sandpaper to get rid of the piiting als also in the combustion chamber.

If the engine holds his idle easy the engine will run fine, maybe not that powerfull als a new one but for sure good enough as training and spare. As mentioned before there is nothing to loose to try this, afterwards you can still decide to get a new one or a new P/S set.

musti72

Off the topic;
I saw some of the racers changing PSR sets, and breaking in the engine again, but they wouldnt be as fast as they were at the first PS set.

Anyone knows why?

rx7ttlm

iTrader: (30)

Suggestion, carefully inspect the rest of the engine. That damage was caused by something being ingested into the engine or a wrist pin clip coming off. If there are other parts, case, bearings(which I would guess where shot) , head button. that need to be looked at. Check the crank, the crank case, back plate, everything. THEN its time to evaluate the engine. If the rest of the parts are ok, you might just go for a piston sleeve, if your conrod doesn't have to much time on it. you might use that for break in. then throw a new rod in it. But your piston has a LOT of pitting on it from what I can see in the pic. The fissure on the side of the piston is now the stress riser and it will fail from there. Find out how much a new piston sleeve and rod are. and go from there. That's what I would do. That gap in ring seal will make the tuning inconsistent and it would annoy me. lol.

Cheers

rmdhawaii

iTrader: (4)

First, thanks everyone for your helpful comments.

This is the second piston/sleeve for this engine. I did a WOT break-in and it ran good for 8 months with no problems. The pinch is still really good. This is my number 3 engine that runs in whatever third car I'm running - so MTX-4 and then NT1. Like I said before, the engine was running good, no problems, so I didn't have a reason to take it apart. Most of my time was spent working on my other two engines.

I took this engine apart at about 11:30pm and I still had to work on my other engine, so I missed some tell tale signs on the piston sleeve that would have given me a better idea of what happened. You know how it is - if you don't know what you're looking for, it's easy to miss things. You guys really helped me pin point the problem.

As you can see from the photos below, a part of the piston clip broke off. See the other gouge going toward the top of the piston? And the pin created a bur on the intake port. Then it looks like it it got caught on one of the other intake ports as the piston was going up, which resulted in the gouge you see on the side of the piston. Rest of the engine looks fine, well - except the button head which I've known about for a while - ha ha, but that's just me being lazy about doing something about it.

I wonder how long this has been here. Maybe months - maybe it happened more recently. Hard to say.

Thanks again. I always appreciative the help I get from the smart guys who hang out here. Enjoy the photos.

Roelof

The piston pin clip must look like a G but now it looks like a C , a tiny piece must have broken off.


Several reasons.
- play on bearings and crankpin
- leak through worn crankshaft
- different portheights on the new P/S set.

DS Motorsport

iTrader: (2)

Something I have experienced which really determined how fast an engine is going to be is the fit of the sleeve into the crankcase.
I have no way to explain this but when the sleeve fits very tightly and it is almost impossible to get it out, the engine is very fast and lasts a long time.

I have had three engines (JP P3L tuned, RB R3 RC, and MF12) which had an extremely tight fitting sleeve, the sleeve of the RB is the worst need to heat the engine before I can get the sleeve pried out with a screw driver.

I had two engines with a very loose sleeve (JP eagle tuned, RB v12 rody) and both of them were paperweights, no power and completely useless.

rmdhawaii

iTrader: (4)

That tightness helps maintain the intended compression, so that you get the maximum downforce after combustion to push the piston down. As you lose the tightness due to engine wear, the compression decreases on the upstroke and that is how you lose power. Compression gauge is a good tool to have if you suspect you're losing too much compression.

The longer you maintain that tighness (aka pinch), the longer your engine "lasts" so to speak.

This is why some people believe that WOT is the best way to break-in an engine if WOT is an option. Not all are designed for WOT break-in. WOT breaks in the metal way different than if you just let it sit there and idle. The theory is, that WOT maintains the pinch longer.

I broke in my Sirio STI and OS TZ (photos) using WOT with excellent results, although the STI is slowly losing it's pinch. I also have the Orion CRF and it is not a WOT eligible engine. That engine is super tight and they don't recommend that you take it out the piston or clean the surfaces either - ha ha.

Hope this helps explain things a bit.

DS Motorsport

iTrader: (2)

I'm not talking about the fitment from the piston to sleeve, that's something i understand.

I do mean the fitment from sleeve to crankcase.
And to me there is no logical way to explain how this affects performance.
The only thing I could think of is a better heat transfer and better support for the sleeve if there is a very tight fitment.

Roelof

A loose sleeve wil have some space for expansion. I had some JP Kangaroo 2003 teamspec engines and bothe sleeves were very easy to take out and both were running great. I think whent the temp is going higher on high RPM with a tight sleeve the piston will expand, the sleeve not and so there will be friction and wear on the piston. When the sleeve will expand with it it will give the piston a better room.

rmdhawaii

iTrader: (4)

I misread that. Sorry, my bad.

CRF sleeve is like that. Nearly impossible to remove cold.

Are you thinking the sleeve expands less outward because there is no clearance between the sleeve and the crankcase versus a sleeve that just pulls right out? If so, perhaps its more significant as the engine reaches the higher end of the temperature range of the engine. But conversely, wouldn't it make sense to allow room for expansion?

rmdhawaii

iTrader: (4)

He he. You beat me to it while I was still composing.