big end cap direction

[tubbyG]

can someone tell me the orientation of the big end bearing caps?.... ie are the notches on the bearings meant to be on complete opposite corners, or both notches at the same end of the rod?

reason I ask is that I picked up my pistons today from getting new rings and bearing fitted....and they have put on some of the conrod caps wrong. some have the bearing notch on the diagonal corner opposite, others have both on the one side :scratch::mad:

The caps are with the correct piston/rod as the tippex I had put on it is still there

thanks

[youngscottie]

Same side
If the caps have been mixed up I'd get some plastigauge in when fitting the crank

[tubbyG]

cheers buddy. much appreciated Crank is already in.......and turns freely :agree::agree:.

the caps are definetley with the right rod though. as they were numbered :)

thanks again

[youngscottie]

For the time it takes I'd still check the clearances on it
If you've no plastigauge a page of the sun newspaper will do

[Tony Walker]

you can see when they fit together and when they dont with them being snapped.

[tubbyG]

thanks for the info :niceone:

just ordered a plastiguage set:)

[youngscottie]

you can see when they fit together and when they dont with them being snapped.

It's been a while. But I can't remember the rods on my 5 being cracked caps
I only mentioned measuring running clearances as I think it's good practice yet often
Overlooked bit like liner protrusion
Spinning freely only means the gaps aren't to tight (read could be to big)

[youngscottie]

It's been a while. But I can't remember the rods on my 5 being cracked caps
I only mentioned measuring running clearances as I think it's good practice yet often
Overlooked bit like liner protrusion
Spinning freely only means the gaps aren't to tight (read could be to big)



That looks cheeky but it's. Not ment to be;)

[Tony Walker]

lol no its fine :agree:

[tubbyG]

so today I was cleaning up the top of the pistons before they go back in.......

I cant believe I never noticed before but 3 pistons from my old (destroyed) engine are dished in the centre.... whereas the one replacement piston is slightly raised in the centre :rolleyes:

so am I right and thinking that the 3 are low comp pistons? and the one replacement is standard?

[GTphil]

Yes that would be the case, you really want to make sure they all match either all standard or all low comp, as you will have higher compression on that on cylinder, and that cylinder will det sooner than the others.

Not sure if the piston can be machined whilst still on the con rod, maybe someone with some engineering skills could tell you for sure.

If it has to come off it can be hard work not damaging the piston during removal, might want to look at getting hold of a single piston then getting it machined and put on the Conrod or getting hold of three standard comp ones. I would be measuring my cylinder head height first tho.

All this is assuming that you were planning on using the pistons in the new build.

[Alastair]

so today I was cleaning up the top of the pistons before they go back in.......

I cant believe I never noticed before but 3 pistons from my old (destroyed) engine are dished in the centre.... whereas the one replacement piston is slightly raised in the centre :rolleyes:

so am I right and thinking that the 3 are low comp pistons? and the one replacement is standard?

Yes = det issues on the high comp one if you advance/boost too much.

[tubbyG]

Thanks for the reply's :).
My initial thoughts/what previous owner told me was that the 5 originally had a standard engine in when i bought it. so all i planned on doing was replacing the fubared piston with another standard one and chuck in the cam.

So next step is to measure the head then will go from there.

Thanks again

[tubbyG]

just had the head measured..... it comes in at 73.292mm

im in new territory here when it comes to comp ratios etc so whats peoples opinions on this?....ok for standard pistons?

im just about to use an online compression ratio calculator, and will try and get my head round it :D

[GTphil]

I would have said that is ok for standard pistons, standard head height is 73.5 if memory serves me right.

It means that of course you will have slightly higher compression than standard so it will det sooner depending on set up/tune. Not by an awefull lot to be fair.

I mean there surely can't be many compleatly o.e height heads around anymore anyways. I think most people say anything under 73mm and you would have to change something be it piston Crown or the chamber in the cylinder head.

And don't forget the uprated head gasket is slighly thicker than standard also.

[tubbyG]

cheers, I was thinking 73.5 was standard depth too

cant quite get the comp ratio calculator to work, wtf is deck height? :scratch:

my carb was set up for 18psi before engine failed and was around 11.7 @WOT... so should be ok once ive run the new one in at the same boost level - but will be extremley cautious when re-tuning

[GTphil]

To be honast mate I haven't worked my compression ratio out exactly so I'm just as much in the dark as you when it comes to the maths. :wasntme: