jim_robson

After the ends letting go on my 205 block engine in my saph I decided to use my spare 200 block engine.

Stripped it down last night, crank looks good, going to get it polished while I'm there and fit new shells. But there seems to be too much movement in the Pistons in my opinion. The block is on a standard bore from what I can work out on the vernier. No real lip on the bore either.

I suspect I'm going to have to go for a rebore and new Pistons, what's everyone else's thoughts?



http://s44.photobucket.com/user/jimrobson/media/E86282CD-6ECE-497F-8484-2A2847743E0F_zpsf7oqminu.mp4.html

Rob_DOHC

iTrader: (4)

They aren't standard pistons to begin with, you won't know whats going on until you remove a piston, measure it and then measure the bore. It does look like too much movement but people often leave a large bore to piston clearance when using forged pistons (can't see what pistons they are from the vid, other than the valve cut outs). Have a measure mate and compare it to fords quoted clearance to see how reasonable (or not) it is.

Also, if the crank looks good then don't have it polished. Polishing increases clearances unnecessarily and can often leave a slightly oval journal.

Rob,

jim_robson

The Pistons do look fairly new, there's no markings on the top of them at all, so I just assumed they were standards with the valve cutouts machined in

jim_robson

Pictures of the Pistons

Rob_DOHC

iTrader: (4)

Looks like they got the valve cutouts in the wrong place lol!

What sort of spec/power are you hoping for Jim, that will probably dictate what to do next.

jim_robson

Will be running t34 on blues mate so around 380-390, can't ever see myself pushing it more than that with the amount of other cars I have.

Is it worth sticking a fresh set of rings in to see if that will take up some of the slack?

My vernier is fucked but managed to get rough measurements

No1- 91mm
No2- 91mm
No3- just over 91mm
No4- 91 mm

Il grab a better vernier and double check it tomorrow

Rob_DOHC

iTrader: (4)

You won't be able to measure to the accuracy you need without a bore type vernier:

Like this: http://www.ebay.co.uk/itm/Draper-027...wAAOSwu4BVuJz1

Cheaper used verniers are available, or more expensive (and better).

That gives you the bore measurement, then you need to measure the piston skirt using standard type verniers (or better!!! a micrometer).

Piston rings don't set the piston to bore clearance, but they would/could allow movement as the ring moves in the piston ring groove, but only movement up to the piston/bore clearance.

jim_robson

I think at the end of the day the only way to get it sorted properly so it lasts a good few years is going to be a rebore and new Pistons? I may as well get it all done and sorted now rather than having to pull it all out again in a years time.

Do you know anyone who can do the machine work rob?

Rob_DOHC

iTrader: (4)

And we are talking about a target bore to piston clearance of 0.05mm for a YB, so I would say your clearance is pretty liberal! and would probably suggest that your engine has previously been built with very wrong clearances.

The standard YB bore is 90.8ish mm, if you are confident about your 91mm bore measurement they might even have installed standard pistons in an oversized bore

I would be stripping the bottom end and having a proper measure.

Rob,

jim_robson

I've text you rob

Rob_DOHC

iTrader: (4)

I would not recommend any body else but HT Howards and co. I have used a fair few places in the past and they are by far the best. Buy the pistons BEFORE you take the engine to them. Specify a piston to bore clearance and leave the block/pistons with them. They will hone each bore to perfectly match each piston and then number them for you (like in the picture above).

I am very picky about engine measurements and when I say they were cock on I can't emphasise enough how accurate their machining has been for me.

Rob_DOHC

iTrader: (4)

PS, ht can also do the long stud conversion, probably wouldn't be a bad plan whilst the engine is in pieces together with a light block reface.

For that power, standard rods with ARP bolts and a new set of standard pistons should be more than ok, just depends on what your future plans are power wise.