severly stumped 2tg/13t hybrid build

[Born-Enthusiast]

yeah i did tighten the clamp enough to still be able to turn the dizzy then after we were content i tightned it properly

[TheToyman75]

Did you find the bits off the pistons ? If so where ?

Its possible that the piston that broke first (possibly Piston 1) sent its debris back up the intake manifold and into the other cylinder damaging the other piston. This would explain the damage to piston 3 as its location suggests impact damage. Piston 1 is most likly detonation.

YOu really should ask your Dad what your base timing was set too and before putting it back together you should really calculate what compression ratio you have built.

[jeffro ra28]

Rod, Im pretty sure its carbied with side draughts, so the debri cant really exist the carbies and then re enter into another cylinder?

[TheToyman75]

Sorry Jeffro, I thought he was running Stock EFI. Good call.

It could do it if he had the factory airbox but is allot less likely

[The Witzl]

This is definitely the result of detonation. I've done this twice with my various 18R-G engines, and they were all because of pinging.

Rod, you should remember the piston i brought around to your place - it had the exact same broken ring lands as the pics posted above. I think i even have one or two of those broken pistons in the garage too, just to remind myself how NOT to do things

Unfortunately, you're going to have to start again with a fresh set of pistons and rings.
Make UBER sure you get the ignition timing right - set the base timing at 5*BTDC and work your way up progressively until you get the right spot. Might also help to check what the total advance is (usually marked on the distributor advance plate that holds the weights). I used to run the 11.5* plate on my 18R-G.... but it eventually leaned out and that caused it to ping and then die.

Can i suggest going EFI?

[TheToyman75]

Karl,

There is no question that Detonation was the problem, I play with 3T-GTE's remember I have seen more than my share of broken ring lands. Thankfully not in my engines

[The Witzl]

A HEMI chamber however is the most detonation proof chamber of them all, however the piston dome is what creates the problems. Thats why it is so important to blend the domes.

So is this a nicely blended piston dome then??

http://www.18rg.com.au/RA28/pistons-001.jpg
http://www.18rg.com.au/RA28/JMR%20Goodies%20017.jpg

** SPS custom make, for my 18R-GTE.



Rod - your brother must be worse than me with regards to breaking pistons!

[jeffro ra28]

Hey Karl,
SPS?

They are of the better ones iv seen! however there is still some work to be done!...lol

[The Witzl]

Specialised Piston Services, in melbourne i believe.

Bah - they are forged so they can handle it

[Born-Enthusiast]

thanks guys, well mistakes are always made with these things i guess, Yeah ha ha i definately need new pistons anyone got some for sale . Don't worry i found all the pieces half of the blow out is fused to piston one . the other half was bouncing around the chamber . Yeah its twin side's so piston three must have been the same issue just without the severity thankfully. My mate asked me why i never went EFI as there are a few i could get my hands on (but then he also wanted me to turbo it ). being under 25 i don't want $3000 insurance so i'm staying N/A as for the carb's my answer . . . What sounds better then twin carb's sucking a volitile mixture of fuel and oxygen into four chambers at high revs down a highway EFI just doesn't produce that same beautifull "I'm killing the ozone with this, and im loving it!" sound.

[oldcorollas]

so.. what do you need to do to negate the requirement of having the pistons flycut?

do the stock pistons fail in the same place? even without flycuts?

[TheToyman75]

Stu,

Even the stock pistons are flycut, just not as deep. I really wouldn't be too concerned about the flycutting. Jeffro has a valid point with the hot spots BUT its something that 999 out of 1000 engines live with at this level of the game. The bigger question is still.

What was the base timing
What does the advance curve look like
Whats the fuel supply and state or tune (afr's at RPM) like
Did anyone check fuel flow
What fuel pump are you using

It really comes back to the two basics, its fuel or timing or both. Its only with these problems that the fly cuts sharp edges will become and issue.

As for why did it take so long to break, clearly at 3000RPM and below it wasn't detonating. The first time it got a decent squirt it failed.

I'd be interested to see pics of all 4 spark plugs actually.

[jeffro ra28]

I think Rod is spot on, my point about hot spots definantly isnt the cause of the problem, just why it decided to fail in that area. Sorry if i mislead anyone with all the jargon i rabbled on about

And yes 999 out of 1000 cases this would be fine. Something else would have to be wrong.

[sillycar chick]

Ive only read through about half of this thread so far, as its a bloody long thread and im at work... but i'll read through more as I can. Sucks about your engine, but im sure we can get it up and running again

Firstly I should ask you, did you do a compression test before you put the engine in your car? If so, can you post up your results? And you said you did another test when it died and 1 and 3 were down, can you tell me what you got on each cylinder?

Speaking from experience, when I built my hyrbrid 12 months ago (my god its been that long?), before I assembled it I took all the measurements I could - bore, stroke, head cc and worked out the dome cc of the piston (this was tricky!), and I also worked out the volume of the compressed gasket. According to my calcs, the engine would have had a compression ratio of about 11:1 or a little over from memory, might have been 11.2. Anyway, it was a bit high as I was going to run standard cam timing.

What I did next was assembled the engine and cross referenced the compression pressure which came up at about 215psi. This probably isnt the way an engine builder would do it, but they would probably have better ways of measuring the piston dome volume than me, and I wanted to check this every way I could. Remember, compression pressure is whats going to detonate your fuel. You can have a high compression ratio but set up your cam timing so that the compression pressure is acceptable.

So, being a tightarse and lazy, and knowing approx what compression ratio and pressure I wanted, I decided to use a head shim. You have to be a little careful and make sure they seal up right, but they do the job. I just used my calcs again to work out what thickness to use. After a few trial and error runs, I ended up with an 0.8mm thick head shim, which got me around 10.2:1 ratio (still a little high but fairly ideal) and around 195 psi on each cylinder. Consequently, If I use anything less than 98RON fuel, my car will ping. If I was to build the engine again, I would probably machine down the piston crown instead, as I have been advised they have enough in the top to do it (mind you I would probably cut apart and old piston first to check).

If you havent checked compression ratios or pressure before you installed your engine, im banking on the fact that detonation has caused this and you need to solve your compression issues before you put this engine in the car again. Your cam timing when you put together the engine is also going to play a bit part in your final compression pressure. Im speaking on my experiences with building one of these engines, but others have also raised some valid points that will also need to be looked at. The more info you can give us about your engine the more help we can give you getting it going again

[jeffro ra28]

sillycar chick,
Did you use stock 3t pistons?
Just curious because i shaved .040"(1mm) of the deck of my block and i got a compression ratio of 11.2. The head has also been shaved but i havent cc'd it yet. So yhe compression is probably higher. There must have been a fair amount shaved from your head block?