Engine REBUILD DIY
 

So what's an acceptable level , I don't mean scores , I mean just barely perceptible with finger nail test and maybe 20mm long , not more than one per bore.

Any one with experience of rebuilding an F20c or other Honda with FRM bores ? Did you have the bores honed ? And was that to an oversize piston

Honing thickness is 0.02mm if the scratches can't be taken out with this then it can be bored to 0.25mm which Honda do an over sized piston for at considerable expense. the workshop manual has all the data and tolerance's for what is acceptable and the procedure for honing,,

Cross-hatching.

Yep the manual has all the specific data , and a set of new Pistons is not cheap for sure , so the questions remain what is acceptable in the way of marks /scratches in the bores , there certainly hasent been a rod failure , piston failure , dropped valve or other misdemeanour suffered by the engine.

Honda also are very specific about the hone and one gets the feeling that even a small over bore is not good , I think it's all down to the initial cast FRM bore with a very high silica content aluminium which forms the hard liner in the rest of the secondary cast block . I recall some where that that's how the bores retain lubricant rather than the normal hone with cross hatch , it's the relatively rough surface of the hard surface of the Ali bores that hold oil!

Its the the hard surface that I dare say limits the rebore , which at 0.25mm means a max depth of cut of 0.125mm including hone . Also one would have to consider any oval in the bores to in the cut depth of 0.125mm

​​​​​​​nightmare re all around really , does one take a chance on these very minor imperfections in the bores ?

Doesn't, sound like it's that bad, you could try just honing it and fitting a new set of rings, firstly depends if the bores are out of round.
Had good success honing and new rings, not tried going over sized, mainly because genuine oversized Pistons are next to impossible to find, they stopped supplying them a long time ago.

Wouldn't it be quicker, cheaper and safer to drop a secondhand complete engine in and sell the existing one?

The net cost to me of doing that with a supercharged Jag engine is about 500 quid and I end up with a motor with half the mileage

Pain in the arse taking modern engines to bits

if you can feel it with your fingernail then it needs dealing with. It'll leak oil and compression otherwise.

a used s2000 engine is minimum £2k and people will want low miles / good compression for that. No cheap options really.

fittimg I guess chip could do but it's a pain in the ass if you don't have a ramp as it's easier to drop than lift

First , it's not my engine sitting in my shed , it's my sons !
It popped out of the top easily with an engine hoist ,

we we are trying a re-build because we can and want to , been talking about it for ages , not interested in a 2 nd hand lump

the engine failure seems to have been a failed oil cooler spewing coolant into the oil , no sign of metallic debris in the oil/coolant mix

Quite possibly if the cooler was changed , engine flushed , new oil and coolant it would have been fine , but he didn't want to risk doing more damage so out it came for rebuild.

Then , maybe hone , maybe Darton dry liners , main and big end shells , rings , maybe Pistons , con rods , oil pump, cams, stem seals and other miscalleneos bits and bobs.

So far looked at bores and found these 3 or 4 very minor scratches , the 2 bearing journals so far exposed on the crank are perfect , odd one set of cam lobes is covered in serious rust with serious pitting

Need to survey/measure bores for wear and oval

Next problem is removing the crank pulley , his snap on impact gun wouldnt touch it , and that didn't even notice my rear hub nuts , so it's 6 ft bars and poles next !

Google research suggests the scratches are not significant, but that's Toby,s call

I'm in a similar position myself at the moment and the info i have read and from past experience on other engines very slight marks won't be a problem so long as they aren't nail deep and don't extend the full length of the stroke, The block i'm using passes both these with just very fine marks on 1 bore, but as it's the first S2000 engine i will have rebuilt it will be interesting to see if it has any effect ,

Interesting read about your cams, i had a hydro locked S2000 in a few months ago, the owner drained and flushed the engine almost immediately and i think did 2 flushes but the cams corroded horrendously to the point of them pitting very badly and rendering them useless, it left the engine with a bad rap until up to temp , so we removed the sump expecting to find the same as the cams but they were in excellent condition,