[Mk2] [Turbo] Pist'on broke

[MATTURBO]

After my car making a "pop" last week it was to be the turbo down so i invested in a nice stage 2 hybrid .

Thought better check the compression ratios and to my ever bad luck the 4th piston was down took the head of and there is a hole in the side of the piston ,the engineering guy said "overboosting"

Strange bearing in mind : Its a rev3 50.000 mile car only run on 1bar in the past 6months out of the year iv had it. With all cooling in place and run on the right oil warm up warm down in the mornings.

So i have no money due to christmas and the hybrid, but then came across these they look good have the right names but im not to clued up so what do you guys think.

http://cgi.ebay.com/ebaymotors/ws/eBayI ... 156&rd=1,1

[Quigonjay]

seems like a good price for the parts
the engineer is probably right, too much boost is a killer of pistons, probably caved in on the ringlands

[Grajey]

Seems a common pison/rod combo.

However, stock rods should be OK providing you aren't building some sort of high revving monster. Deffo worth considering if budget is tight.

The extra cash may be better spent on bore/hone and new bearings etc.

HTH

[MATTURBO]

Ok thanks guys yes budget is tight but its knowing where to get the rest of the bits cheaply form else where e.g big end shells etc...

I thought maybe just the pistons would be ok as iv heard the stk rods are good for high power.

[matt_mr2t]

Dont 86.5mm pistons require some honing of the head to accomodate them?

[TBDevelopments]

yes you don't want to just drop a set of pistons in, you want to check all your bores for signs of scratches, make sure the correct clearances are there for forged pistons and give the bores a light hone to get them upto specs.

If it helps i've got a whole line up of pistons of different makes and sizes instock that i can probably help you with. After you add tax to that us price i bet i'm not far off the price either. Plus you can have them asap if needed.

Hope that helps.

Tim
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[matt_mr2t]

So am I right in thinking that if I wanted to get a set of forgies I would need to take my engine appart first before I even know what's best to buy?

Or could I just buy 86.5mm pistons and get the head worked on to accomodate them?

[TBDevelopments]

its always best to fit the smallest piston bore you can get away with for block stength.

The other way is to just buy 86.5mm pistons as you said and machine the block to fit them but this is a backwards way of doing it really because 99% of the time if the bores aren't damaged you can drop 86.00mm straight into the bores, or if there a little tight a small hone which can easily be done with a drill and honing stones which can be bought from most places, even halfords i think.

With the 86.5mm you'll need to strip the engine and have it rebored so much bigger job.

The 86mm can be done with block in the car if your careful and make sure everythings clean afterwards, not ideal way but certainly possible for just a piston upgrade.

Tim
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[matt_mr2t]

Cool, I'll keep that in mind Tim, thanks.

[Grajey]

If the bores do need as re-bore you can consider 86.25 pistons. I used these in my rebuild. Car now running well at 1.4 bar thank you.

I used Clevite bearings, from Tim, for big end and mains.

HTH

[llenrub]

I have this combo on my vehicle. I paid much more than that. This combo is as good as any.

At that price...... go for it !

[TBDevelopments]

yeah the 86.25mm is a good comprimise, i've got some coming over soon for this reason.

Tim
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[Jimbob]

I've got that exact same set-up in my car mate, from that guy. The pistons are lovely, my builder was well impressed. The pistons were so good he said theres no point in even trying to balance them.

Those rods are a fairly standard option and good allrounder.

My advice is to buy from the US, I also got main studs and a cometic HG from this guy. He is very good, cheap, and delivery is very good.

Lets put it this way it IS a heck of a lot cheaper than buying them here. I paid tax's and shipping through fedex and it was still considerably cheaper

From a reputable UK reseller a rod/piston package is about £650. At the current exchange rate those ones are about £400 inc shipping, IIRC I paid about £100ish for import taxs. So all in all your looking at no worse than a £100 saving and they were here in 3 days!

Secondly you CANNOT hone with a honing stone from halfords. A hone is basically a fancy drill bit. After boring you will still have machine marks in the bores. A hone runs inside the bore and basically cleans it. They can be staged as well, getting ever closer to the actual bore size, hence cleaning more and more, getting a really nice surface finish. A skilled engine builder may then chose to hand finish. If you use a honing stone there is no way you will keep the bores circular, and there is no way the rings will seal.

Jim

[TBDevelopments]

not seen the halfords type jimbob but a honing stone are centralising, you can't oval a cylinder using them. This would be the same type a engine builder uses to hand finish them.

When i was refuring honing this is what i ment, stepped stone coursness and accuratly measuring all the way.

Didn't mean just throw some old stones in there

Tim
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[Jimbob]

A honing tool looks something like this tim



or this



Not this, which is what you get from halfords and fit to a drill!



With a honing tool you start at just under your desired bore size and slowly adjust to get it absolutely spot on with minimal machine marks. But if you know a way of fitting a 3 axis support to a block whilst it is in a car and then honing to an adequate level of tolerance I would give up selling the pistons and take up engine building

Jim

P.S When I said buy hand I meant by hand with some fine emery paper, you cant hold one of those bits between your hands and twiddle it like your starting a fire, ray mears syley!

[MATTURBO]

Well i have checked my finances i really cant afford them so im getting all the pistons checked tommorrow if its just the one then thats all ill replace is the cheapest option that will do the job fine, Ill also need to replace all big end shells and all Gaskets.

Total with Gaskets, one piston and shells around £300

Total with Gaskets, forgies and shells around £700

Any thing else i could replace for upgrades for little extra cost while im doing the job ??

[Jimbob]

If it helps I have a set of used Rev2 Pistons? They are in good nick and only covered 30,000miles, have no rings but are just laying around, yours cheap if you want them mate

Jim

[MATTURBO]

Mines a rev3 matey and i think if its gonna be replaced ill try and scrape for a new piston

Thank you for the thought anyway

[TBDevelopments]

PMSL jimbob, that bottom picture isn't even a honer its a grinding bit on a drill attachment.

You can get a honing machine for a hand tool identical to the centralising tyre pictured above, which does exactly the same job. I know a few engine builders don't even use the bench tool version as they proper the hand tool version of this.

Tim
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[TBDevelopments]

like this for example.



the idea of giving the cylinders a hone isn't to remove imperfections and machining marks as you call them (although they can be used for this) is to create a cross hatch pattern in the bores to prevent a vacuum seal from the rings to allow oil to collect in the cross hatch to provide greater lubrication during engine running.

The type above is self centralising so a solid axis isn't needed to give a good job, the drill can move around while doing this job and it will have no effects of the way the stones impact the cyclinders. Like i said i know alot of engines builders who don't even use the vertical honing machine and profer this method, the only advantage to the honing machine is the up and down rythm which can easily be mastered to the same level by hand with some practice.

There is also ball type honers like this



although these are more used for small cylinders like that found in brake calipers where the other tool is to big to use.

just because i don't sell built engines jimbob doesn't mean i haven't built my fair share in the past

Tim
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