Welcome to the Austin Seven Friends web site and forum

As announced earlier, this forum with it's respective web address will go offline within the next days!
Please follow the link to our new forum

http://www.austinsevenfriends.co.uk/forum

and make sure, you readjust your link button to the new address!

Welcome Austin seven Friends
This Forum is Locked
Author
Comment
View Entire Thread
Re: Cylinder Block Failure

There are ways of causing this without lumpy cams and powerful bangs: It the crankcase top/block bottom is not flat as is so often the case, extra strain can be put on the brittle material where studs are pulling down and pistons kissing the head can also create big forces here. My own block lifting trouble was caused by pistons nipping up during running in. It turned out the pistons i had bought were round and a bit meaty round the gudgeon pin bosses so expanded too much there. W

Re: Cylinder Block Failure

Winston Teague
There are ways of causing this without lumpy cams and powerful bangs: It the crankcase top/block bottom is not flat as is so often the case, extra strain can be put on the brittle material where studs are pulling down and pistons kissing the head can also create big forces here. My own block lifting trouble was caused by pistons nipping up during running in. It turned out the pistons i had bought were round and a bit meaty round the gudgeon pin bosses so expanded too much there. W


A number of years ago when some of the early Australian pistons appeared in the UK I had similar problems for the same reason.

Location: New Zealand

Re: Cylinder Block Failure

Austin in the Shed,

"Even though the block had been bored out as much as to leave 1mm around the lower cylinder area, given the whole area including the tappet chest material I can't see how it would break up like this in such a short time unless something mechanical had happened."

I think from recent advice it was also a supercharged engine.

"If it was a repro block what was the need to liner it?"

For some unaccountable reason it appears the Renault wet liners may have been fitted to a new reproduction block - perhaps to see how far a block would go before failure.

If the pistons were hitting the head I would have thought the diesel like noises might have alerted the builders- perhaps this couldn't be heard above the supercharger noise.

The picture does seem to show the nearside (cam side) studs may have pulled out - possibly first, although this could have happened after the very thin offside of the casting failed.

Tony.

Location: Malvern, Melbourne, Victoria, Australia.

Re: Cylinder Block Failure

us traction engine boys have problems with crank whip and pistons hitting the ends of the cylinders. On a steam engine both ends have heads!

2 bearing cranks, 2 1/2 foot + between bearings.

Re: Cylinder Block Failure

I have only had one instance of block/crankcase joint failure and this was studs pulling out of the crankcase complete with part of the casting.
I'm pretty sure this was caused or at least aggravated by the nuts working loose which I noticed happening on that engine. In this case the forces increase dramatically.
If my memory of Mechanical Technology lectures serves me right serves me right the force of applied loads varies dramatically depending on how this is done.
It's easily demonstrated with a spring and a weight. If a weight is suspended from a spring and the spring allowed to take up the weight gently it simply stops at the extension of the spring that exactly balances the weight. If the weight is then lifted until the spring is just relaxed and then let go the weight will descend twice as far as in the first instance. ie The force is twice as large. However if the weight is raised even higher and then allowed to drop the distance it drops will be very much greater indicating that the force is very much larger. I believe that this increase is exponential.
With the block firmly bolted down I imagine the forces are somewhere between the first two cases. ie Somewhere between the calculated force from springs and power stroke and twice that figure. However if the block is loose we're in the third case and the force increases dramatically. I'm sure this would strain the block casting.
I no longer use the paper gasket between block & crankcase but stick it down with Threebond 1184 and use new spring washers. This makes a very strong joint indeed that is very unlikely to work loose. The only problem comes trying to dismantle it.
As an aside I'm wondering how close nos 2 & 3 pistons would come to a high compression head. I also have an 1-1/8" Phoenix crank which I suspect may whip more than a 1-5/16". Does anyone know how much clearance it would need?

Location: Melrose, Scottish Borders

Re: Cylinder Block Failure

Tony,

My last Austin was bored out to +80 to take R4 pistons which I thought was fairly marginal in terms of the remaining wall thickness, but it still seems to be holding up on an original block. The Usual mods were necessary including skimming the crowns down and the skirts, although to help get round the longer pistons I also took out the cocoa tin lids in the crankcase - evidently this then meant the plugs oiled on a regular basis and not particularly advisable with a splash fed engine! This is all fairly irrelevant, if you do what that numpty engineer has done.. but thought I'd add my thruppence worth.

Nick

Re: Cylinder Block Failure

Another theory,The engine has run hot,especially if supercharged,running weak or tight due to rebuild and the pistons have nipped up in the bores and tried to pull the block off the crankcase..

The A7 JP pistons were bad for that sometime ago and needed relief around the gudgeon pin area to stop them picking up..

I managed to bore a block 4mm oversize,It was great for about 150 miles until the side of one bore fell out.

Re: Cylinder Block Failure

The interesting pinterest page (R. I have logged in as you suggested and can now see all again- thanks!) shows the ten base stud Grasshopper block in great detail.
As well as being chromidium as noted, the five block base holes on the offside are in line - with the three centre holes noticeably in from the edge when compared to the standard block, as well as having substantial vertical ribs on each cylinder.
R, in an earlier forum exchange on boring cylinders you note that in your experience 80 thou re-bore is usually the safe maximum, with potential problems over this especially on later blocks.
Discussions on the internet on sleeving suggests that glued in dry liners can be used - but I would think that this could conflict with the need for good heat transfer between the liner and block.

Tony.

Location: Malvern, Melbourne, Victoria, Australia.

Re: Cylinder Block Failure

hi tony

Agreed, glued in liners seems a diabolical idea. The piston crown represents a large proportion of the heat absorbing area. Some transfers via oil drops but the bulk flows out through the skirt and rings, particularly the latter.
A glued liner would offer erratic heat transfer resistance leading to distortion and worse.

Bob Culver

Location: Auckland

Re: Cylinder Block Failure

I guess you are just behind the times. Over the last several years it's become common practice, actually.

Re: Cylinder Block Failure

I suppose an abiding interest in Austin Sevens strongly suggests a slight tendency to be 'behind the times'

Tony.

Location: Malvern, Melbourne, Victoria, Australia.

Re: Cylinder Block Failure

I am about to place for sale on ebay an Austin Seven engine block. This block has been previously bored to take + 4 pistons. I assume that it will be ok to rebore further up to + 6 without the problem of failing like the ones mentioned in this thread. Your views will be appreciated.

John Mason
Nottinghamshire

Location: Nottinghamshire

Re: Cylinder Block Failure

Should be fine.

Re: Cylinder Block Failure

I agree with Alan, subject to thorough inspection, and provided that there are no deep scores or lips in the bores.

Re: Cylinder Block Failure

John Mason
I am about to place for sale on ebay an Austin Seven engine block. This block has been previously bored to take + 4 pistons. I assume that it will be ok to rebore further up to + 6 without the problem of failing like the ones mentioned in this thread. Your views will be appreciated.

John Mason
Nottinghamshire


john, sell it as is and dont worry about it.

the truth is each block is different.

from new the castings had movement in them, ie if you look in the valve chest some are machined behind the springs, some are not. this is due to movement in the castings.

the centreing on the bores can also be different, due to movement.

then some blocks will corrode in the water jacket more than others. witch means a block is not always garanteed to bore to +60

i`ve even had blocks that were poorus from standard, and leeked water into the bores.

then take in the fact that when your block was bored to +40 it may not have been done centre to the bore.

then when you start machineing/reconditioning. you start to find were the cracks are.

the buyer takes his chances.

Location: back in the warm

Re: Cylinder Block Failure

And presumably can be sleeved back to standard (glued in or otherwise ) if the worst happens.

Tony.

Location: Malvern, Melbourne, Victoria, Australia.

Re: Cylinder Block Failure

Mention was made of pistons binding across the gudgeons. Some newcomers may not have seen or taken note of the original equipment Austin made wide ring solid skirt pistons. These were turned circular but relieved in a semicircular pattern around the gudgeon so that the full diameter was retained immediately above the 3rd skirt oil ring. Thus crank flex and imperfect alignment accommodated. I had noticed that aftermarket pistons of the same pattern omitted the relief, and used to file it in.

I note the wrecked engine had steel oil rings. In response to a previous enquiry I was advised that very low oil consumption is routinely achieved with modern narrow comp rings, including without baffles, without resort to steel oil rings. Many used to reckon steel oil rings sapped excessive mouse power out of stock engines.

Bob Culver

Location: Auckland

Re: Cylinder Block Failure

Renault 4 pistons often have a spiral back up spring behind the oil control rings. I always leave this out when putting Renault pistons in a A7 engine. It does exert quite a large pressure on the cylinder walls, which as Bob says can't do the power output any good. I never noticed a problem with oil consumption or plug fouling doing this.