Patches in bores in freshly machined block.

[JonnyWowsers]

Hi Guys, I'm wondering if someone can either A: put my mind at rest or B: have me scrap this lump off before I throw any money at it.

I recently overbored an A series Engine to Vizards supposed maximum of 74.7 as the 1380 was tired.. With all due respect I'm not really here for a debate on reliability issues, the bores are offset and I have as much meat between the bores almost as an un-offset 1380 and they do the job. anyway that's not why I'm here..

Having machined the block ourselves(me and the proverbial my mate) on a 2 year old Hurco cnc, everything went lovely, nice finish leaving a couple of thou in for honing. When we examined the bore there are odd shall we say extra shiny patches as if either a change of material or the like. We at first thought because they are on the side wall it cud be any vibration caused whilst machining is dampened as it passes where one cylinder 'touches' the next, ie less vibration causing a change of finish but these patches arent all the way down as you might expect if this was the case.. I know it's not due to thin wall as again they are only there where it is a solid casting not a water jacket..

I would appreciate if someone else has encountered this that they could enlighten me..

Also there is no geometrical change at all (not even a flicker on the clock) using a micron bore comparator.. Regards...

Edited by JonnyWowsers on Monday 11th March 12:27

[cmsapms]

I believe that when the blocks were cast, various lumps of metal (steel) were embedded in the casting sand as a way of tying bores together. One of Vizard's books mentions these (including a picture, IIRC) as a potential pitfall of extreme overbores. The advice is not to worry as they're unlikely to give a problem - certainly less of a problem than your rings are going to have trying to seal against your floppy bore walls; but you didn't want to discuss that

Good luck.

[PeterBurgess]

The inserts for supporting the castings are called chaplets.
It would be better to have some pictures of the aforementioned 'nasty'

[JonnyWowsers]

Thanks guys. I'll get sum pics on in a bit. So would these rods 'be as one with the casting' or should I assume due to the dissimilarity in materials and melting point etc. there is no penetrative fusion between the steel and cast block? Its basically just encased..? Sorry about the 'not here to discuss reliabilty' comment I didn't mean to sound like a tw#t.. Its just a bit of a cheapo pet project if it's a bag of unreliable crap. I'll transfer all (except pistons obviously) to a fresh 73.5mm 1380 block.... Regards Jon.

[PeterBurgess]

I have only seen chaplets showing up in the bores of B series engines ( usually when we up the bore from 80.26 to 83.5 to get a 1950 cc), probably as we do not build many A series engines, I guess about 30 all the time I have been engine building. We have probably built 300 B series engines so have seen more chaplets, maybe a dozen blocks. They usually look like a capital H with casting material around them, I have never seen one move and have never seen a failure caused by the chaplet breaking into the bore.

[JonnyWowsers]

[JonnyWowsers]

Photos of machined bore prior to honing... I'm getting the general consensus this will cause no problems...?' ( ps. have been trying post this for days "piston heads said no posts from' 'new' members due to online abuse?!?)

[Boosted LS1]

I can't see there being a problem with that. Those marks would be below the ring pack anyway? I once had an overbored block which had water marks on it. On reflection I think it was porous.

Your 'marks' have straight ages and as Peter has suggested look like metal inserts placed into the sand cores at the casting process. They'll provide stability to the cylinders as the metals poured and cools.

Edited by Boosted LS1 on Saturday 16th March 09:29

Edited by Boosted LS1 on Saturday 16th March 10:43

[JonnyWowsers]

Thanks boostedl1.. 👍

[PeterBurgess]

As Mike says, looks like chaplets, hopefully all ok.
Is that just a bored finish ready for honing?

[Mignon]

PeterBurgess said:

As Mike says, looks like chaplets, hopefully all ok.
Is that just a bored finish ready for honing?

Maybe where he said "Photos of machined bore prior to honing" would be a clue to the observant.

[PeterBurgess]

The poster said a couple of thou left for honing didn't say he didn't hone it did he?

[PeterBurgess]

You are quite right about the photo bit Dave. I should have gone to Specsavers (other brands are available).
Put it down to post leading then losing Rugby England vs Scotland
Then England back from the dead!!!!

[PeterBurgess]

Then a draw!!!!!

[finlo]

Not much meat between the bores for the head gasket!

[Boosted LS1]

There's not much meat between the bores for a head gasket.

that said there's probably plenty ;-)

[PeterBurgess]

It is a fairly common practice to place a strip of copper or even stainless wire between the bores on the overbored A series to help with the gasket integrity.