my 5 let go today - whos going to guess what it is

[gttjames]

had a few months use out of her this year anyway and done about 2000miles in it. Have had it running 20psi on a tomcat for last 500miles, standard main, 1.3mm 2nd stage, 1.1AC, phase 1 'uprated' fuel pump, fuels well, 11.8's sometimes slips to 12.0 WOT

Today a few blasts all day been fine, then suddenly started misfiring on low down revs and see the white smoke behind - took it straight home, temp gauge creeping up higher than normal so lucky didn't have to go far.

symptons - white smoke lol, exhaust fumes in header tank, coolant below min, and mayo in rocker. Whos going to guess what it is then, cracked head, headgasket, cracked liner?

Il do a compression test tomorrow and whip the head off and see what it looks like

vid of it recently
http://www.youtube.com/watch?v=h7Vc8cFtJiQ

[Nottswoody]

Just out of interest. What did you do your head lots to? Torque wise that is.

[R5MJH]

sounds like hg has let go matey to me

[Brigsy]

H/g or liner. Possibly down to det, did you listen for knock when setting up?

[GTphil]

All being well it will just be the gasket, at least the sump can stay on then.

Whatever has happened the most important thing is obviously to find out why

if it's been detting it will be easy to tell.

Pissed me right off when my 3k old lump went pop!

You could always fire bomb it and have done with it

[Pigsnake]

Gutted for you james.

[gttjames]

I know, oh well il get it off asap and see whats what, hopefully I don't have to do bottom end.

notsowoody - standard torque was 60nm, and seen people say upto 90nm so i did mine at 75nm

yer i did listen for det with some stethoscopes from work, they wernt long enough so i extended the pipe through to engine bay, wasn't the best tool but all sounded ok to me on set up. Yer just need to find fault and cause so it doesn't happen again

[kial]

Had the same symptoms happen to me last time mine went. Ended up being hg failure down to det.. Was getting all the right reading on afr so was clueless when it popped. Couple of guys on here mentioned it could be cause i was using 95 rather than 97 fuel.

Hope you get it sorted soon mate

[VALE46]

Sorry to hear that James

[gttjames]

It happens just keen on sorting it so it doesn't happen again

Flywheel end 1 2 and 3 where all 155psi - 4th water pump end was 145psi

Head came off and was clear where it's blown the gasket apart between the fire ring and water way. No signs of det on piston or head but been told still could be det.
Liner protrusion all good.

If fueling was ok but it still dets how do you stop det?

The head is from a member on here and has had the squish are shaved to regain oe area compression from being skimmed. I also have got a oe thickness head. Which shall I use?

[R5MJH]

as i said yesterday sounded like hg let go, what does the head measure matey

[R5MJH]

also are those pressures WOT

[Matt@CodeRedMotorsports]

Is that a crack?

[gttjames]

as i said yesterday sounded like hg let go, what does the head measure matey

I knew it was going to be that area, liner/gasket/head - glad its not bottom end as they where all new liners a year ago

[gttjames]

also are those pressures WOT

no there just cranking pressures with plugs out

[gttjames]

Is that a crack?

good eyes matt but no its a scratch

[gttjames]

what do the oe knock sensors that bolt on the head do? as I still have it in place but if its no good il bin it, less junk in the engine bay.

In a dilemma now. which head to use

head that came off - measures 73.0mm - modified squish area as you can see from pics, and polished throats in the head

head no2 - 73.5mm - so never been skimmed

what to use?

(obviously which ever I choose to use will be getting tested 1st)

whats going rate for a pressure test and skim these days?

[R5MJH]

think there abit on the high side mate, the psi on mikes are all 130 psi but when the throttle is held at wot they are all 145 what they should be, we had your psi on old head which was over skimmed, we had 155 and 185 wot which kept blowing hg, we now use a 73.3 ml head and a 1.9 blue meillor to get the above results 130 and 145 wot perfect matey

[Brigsy]

I would use the 73.5mm head matey. I imagine the compression is higher than standard at 155psi.

Check it with a straight edge, might not even need a skim

[GTphil]

A wise man said said to me that high comp and pulling timing generally makes more power than low comp and adding timing.

More chance of det with higher comp so harder to tune with really good det detection,

Standard comp is right in the middle, plenty of people have ran 22psi plus on standard comp with no issues.

I would also be checking the vac capsule in the a.e.i

[gttjames]

think there abit on the high side mate, the psi on mikes are all 130 psi but when the throttle is held at wot they are all 145 what they should be, we had your psi on old head which was over skimmed, we had 155 and 185 wot which kept blowing hg, we now use a 73.3 ml head and a 1.9 blue meillor to get the above results 130 and 145 wot perfect matey

Well it's strange because after I'd done about 1k miles I did a compression check on it just to check and was getting around 135psi. This time I used a different kit but got above readings. Would having water in the bores give a higher reading?

[gttjames]

I would use the 73.5mm head matey. I imagine the compression is higher than standard at 155psi.

Check it with a straight edge, might not even need a skim

Yer I'm thinking so as well. Checked all the head here with a straight edge and all are down in the middle. Is there a tolerance? It's about 0.15mm

[Matt Cole]

IMO, it doesnt look like detonation. Theres somthing iffy looking about that head? The mating face around the combustion areas doesnt look even and by looking at the compression marks on the fire rings, i would say it hasnt been set to the correct torque?

IMO of course

[R5MJH]

IMO, it doesnt look like detonation. Theres somthing iffy looking about that head? The mating face around the combustion areas doesnt look even and by looking at the compression marks on the fire rings, i would say it hasnt been set to the correct torque?

IMO of course

agreed matt also like brigsy said put new head on with a blue meillor 1.9mm gasket and tighten to 80nm as james5 told me, mikes is flat out most days with no problems mate, also check piston comps before running ours were 130 without pressing the accelator and 145 with pressing WOT, without ht lead on of course, report back once done boss good luck mick

[gttjames]

the 73.5mm head is at machine shop getting skimmed, its a shame it needed a skim but hopefully they don't take much off.

old head was torqued up fine, but will go to 80nm this time

also the guy at machine shop said it looks like det to him, cheers for all replies so far

[DaveL485]

Looks like something I did a few years ago when experimenting with higher compression. I went to almost 9:1 at 17psi and it popped the HG just like that. Same as you, no sign of other damage.

If you get det, or pre-ignition (they're different don't forget) the sudden, massive spike in cylinder pressure does this. The det shockwave of 2 flame fronts colliding or from a pre-ignition event with the piston on the upstroke will be more than the seal can cope with.


My heads go on at 75lb/ft, btw (Just over 100nm), but then it is a 21 lump.