severly stumped 2tg/13t hybrid build

[Born-Enthusiast]

Hey guys,
Just to recap I started building a 2tg/13t hybrid in about feb 2006. After a huge delay I finally got the kick in the pants to finish the job. (now i know how project cars can just be left in a shed for years) Any way I was well on my way I got new pistons and then got the pistons flycutt, got a lightened flywheel, proffessionally reconditioned the head, bored the block one stage, honed and faced it of course, got all the peices together and started assembly. I was very carefull to get it right as money is quite tight so I didn't want any mistakes I completed the build and did a check to see if there was any hitting of valves or anything grabbing by turning the crank with a spanner. It was all good! I was exstatic and really exciting to get it in i'll put photo's up when I can, I have the whole rebuild snapped. Sorry a little of the subject. My dad was very particular about the timing and was watching over my shoulder when it came to getting it right, he wanted to make sure detonation was definately not going to be an issue. I ran the engine in for 974KM, never going over 3000rpm (this was torture I just wanted to DRIVE IT!!! ) before changing the oil and oil filter. Now this is where the problem began. After I changed the running in oil out I took the car for a drive I was in it for about two hours still not really driving hard as I didn't want to push it too soon. I only took it up to about 4000 RPM after picking up my mate we went for a little drive due to traffic and me trying to merge I took the engine to 5000RPM it was great! Then a noise developed, curious I pushed in the clutch to see if it was happening at idle and my engine stalled WTF! I pulled over and popped the hood couldn't see anything so that was a good start then I tried to start it . . . nothing... so we push started it the noise was horrible I knew something had broke. I got home and did a compression check. I had lost compression in chambers 1 AND 3. I took the engine out. After pulling it out i checked the cams, no all in line so it didn't slip and hit valves, i pulled of the sump and checked bearings, no everything is fine! I pulled off the head and my heart dropped. Piston one had blown a chip off the inlet side. When i pulled out the pistons i noticed a crack in piston1's ring seperators and piston3's ring seperators where both cracked twice! Without any bent vavles, detonation, piston hitting the head or any other visable signs I am stumped. Who's fault is this and why did it occur?!? Is it a piston failure? I've taken photos and will post them as soon as I can please any help will be very appreciated I can't rebuild my engine till I find the cause so it won't happen again thank you for your help I hope to hear from anyone who can give me an answer

[TheToyman75]

Please post detailed photos of the broken pistons and pics of the combustion chambers.

what pistions are you using

What fuel system are you using ? Carbs efi etc - Detailed

What was your base ignition timing

What compression ratio was it built to

what spark plugs ?

What fuel ?

[Rinmax]

This sounds very familiar to a hybrid i built a little while back. Went throught the same type of build up, ran it in to my liking and then had it dyno'd. All was fine so i hit the race track. First outting I broke the number four piston, with a chunk missing from near the flycut section.

The big differance with mine is that I belive it was fuel related. Mine started to ping at high revs (7000) and within a second of the pinging starting she broke. I think that I just didn't get the enough fuel in the engine. This has now been sorted with a new fuel pump for the new engine.

I belive that your problem is different than mine, but each may shed a little light on the others. I look forward to seeing some pictures to try and give you some advice and/or opinions. It's a bit hard to take a stab at the cause just yet but I'm sure the people on here will be able to nut it out for you.

[Born-Enthusiast]

i only use 98 ron fuel i have some issues with my technology at the mo so i can't get the pictures up yet i have taken them tho

uh the exact ignition timing i'd have to ask my dad as he help well did the timing mostley i held the tools ha ha

uh im running twin sidey solex's i think they are 40mm

the sparks are i think the brand is KNG they are the quad spark type with the 4 prongs in them

compression i hadn't built it to anything i just put it together and was unsure what comp it would be

the pistons i ordered thru dave at sleeka spares as with everything else i also used their machine shop worker and the fly cutt was done to previous build that runs fine producing i think they said 80 or 90 KW ATW

[Born-Enthusiast]

thanks rinmax yeah its a bit hard to judge withou my photo's up im trying to get them up asap

[Rinmax]

most hybrids will do 80 - 90 rwkw. so your right on with the power mark.

Lets just try to help you get this thing going again. There aren't enough 2tg's on the road

[Born-Enthusiast]

your not wrong mate they are a beautifull thing

[thechuckster]

pics of the plugs would also be helpful as they'll show if you were running lean or rich or other.

is there any shallow pitting (might look like small nail hs gently tapped the surface) on the top of the pistons or the head - these would be detonation


you original post suggests your took it very easy on the engine while bedding in the rings and running the whole engine in - did you:
-put it under varying amounts of load (a good thing) like a highway drive over underlating roads
-avoid long periods of idling (also a good thing)
-run it very rich to avoid detonatioon (bad)
-do lots of free revving in the garage (not very helpful)
-go gently on it and not make it do any reasonably hard work (also not helpful)
?

[Born-Enthusiast]

I tried to get it to do a bit of work. i drove it with only me in it and with a full car i don't think i was driving rich my dad tuned it for me didn't do a lot of free reving only when we tuned it i didn't want to do it too much the only real idling periods was warming up and at traffic lights of and the tuning process i also varied the speed i took it to 3000RPM :/

[merc-blue]

deffently sounds like detonation, not valve hit or poor assembly
put up more details on comp ratio/timing/fuel setup
how was the timing setup?

[Born-Enthusiast]

ok so i got my thechnology working with me took a bit sorry about the delay but yeah sorry if the pics are blurry i sprained my wrist and it was hard holding both piston and camera still enough ok so this is piston 3 with the cracked ring seperators (i don't know what to call them)
heres a closer shot
this is the peice missing

this is piston 1 oh its a sad thing
this is it from the exhaust side
sorry there isn't more off piston 1 the others were too blurry


so this is the head on chamber 1

this is chamber 3
and as a comparison chamber 4

don't worry about the silver dots they are carbon or where carbon isn't one of the two its what the flash did without the flash its too dark

[Born-Enthusiast]

for example this is chamber 1 without a flash but the others are blacker this barrel looked as tho it was not getting as much fuel it cleaner but that may have occurred after the problem as i did have to drive it home

[Rinmax]

The picture of the no 1 piston with is missing bit at the flycut, is identical to my damage. Basicly I have put it down to detination.

Looks to me that you will need a new set of pistons and have another go at the timing and fuel delivery.

[jeffro ra28]

I noticed the piston crown have not been blended at all. Still all very sharp edges.
The section which has broken away from the fly cut section is very thin and sharp. This area although right next to the fresh charge from the intake valve, was probly creating a hot spot in the chamber and causing pre ignitio/detonation. The Duralite ACL pistons (which is what they look like) are hopeless for detonation resistance so this is a very important factor to consider.

May i also add that it was probly run in a little on the soft side. If you did it how you have described. They shouldnt be babied to much, it wont hurt them to give them a little more revs, it should actually help with the run in.

[Born-Enthusiast]

Looks to me that you will need a new set of pistons and have another go at the timing and fuel delivery.

you are not wrong ha ha only thing is i don't want this to happen again as why im trying to figure out the cause thanks for your help guys