Cracked (newish) B18 pistons

[mocambique-amazone]

Ok Sam, a too wide gap is no problem. A too small gap is a prob.
Can you feel a step on top of the bore? Often people mount new pistons in a used bore with a step. And the new pistons don't have the same position as the old... they run into the step. This, and a lot of pinging will result in cracked pistons like yours.
The dark colour on the back is caused by overheating, I think the engine runs too lean at higher revs, and with pinging too.
I don't think that the pistons hit the head, there are no marks visible.

George: A easy way to test if the seats are worn out is to remove the rocker arms and put a straight edge on top of the valve ends. The ones with a worn out seat are much higher.
If the seat is gone like the ones from Sams engine they are dead. And like Sam did you have to check amnd adjust the play in short times. If you won't you risk a cracked of valve. You can't repair this head without new valve seat rings. reseating would be stupid. Stupid people do this and shorten the valves to hide the prob :-(

good luck, Kay

[classicswede]

Originally Posted by mocambique-amazone

Ok Sam, a too wide gap is no problem. A too small gap is a prob.
Can you feel a step on top of the bore? Often people mount new pistons in a used bore with a step. And the new pistons don't have the same position as the old... they run into the step. This, and a lot of pinging will result in cracked pistons like yours.
The dark colour on the back is caused by overheating, I think the engine runs too lean at higher revs, and with pinging too.
I don't think that the pistons hit the head, there are no marks visible.

good luck, Kay

I think not enough piston clearance and or a lip at the top of the bore could well have been the issue.

Not with B18's but I have come accross new pistons that are slightly over size and that could well be what we have here

[woodman]

A few years ago I had a B18 engine rebuilt with a 30 thou rebore. The rebore, honing etc was done by a reputable engineer in Sheffield. The pistons and everything else came from Brookhouse. For the first 15,000 miles it ran as sweet as good be, I was delighted. Then one day I pulled away from a roundabout and BANG, horrible noise, loss of power, you name it. I managed to limp home but when we opened the engine up we discovered that the culprit was a cracked piston - the crown had simply broken off.

When we compared the new pistons with the old ones, the main difference to note was how much less metal the new ones had. The new crowns were basically held on with three thin webs, whereas the old ones were very much integrated parts of the casting with holes bored through for the oil ways.

Simon Brookhouse said he'd never known it happen before, but I have spoken to him again since and he said he is now using a different supplier. He also said he thought the supplier would be certain to disown responsibility for the problem on the basis that it was out of warranty and could only caused by bad timing. I was frustrated by this as I was confident the timing was good, based on it having been set up properly, running well with no pinking. But I had no come-back, unless I'd had the engine post-mortemed by a different auto engineer from the one that did the rebuild.

Until now I've never heard of anyone else having this problem, but your story seems remarkably similar, and personally I'm inclined to suspect poorly manufactured pistons. For what it's worth almost every single problem I've had with my Amazon, aside from inherited wear and tear, has been the result of rubbish parts. It's extremely disappointing and costly. My heart goes out to you, Sam.

[swedishandgerman]

I was wondering if you were going to chirp in the Andy Woodman as I well remember your woes on your engine with newly fitted pistons.

Sam, if your engine was rebuilt by who I think it was rebuilt by (I think I remember who), the pistons would almost certainly have been supplied by the same as our man Woodman's. As well, from memory, your engine, Sam, was rebuilt approximately the same time give or take a few months as Andy's. If it was built up by who I think I remeber it being done by, i would be very surprised if they did it wrong.

Bad blimmin' luck on poor quality parts here again, I'd say. But based on what Andy has said that Brookhouse now source their pistons from another supplier, it seems like you're not the only two...

[swedishandgerman]

Oh! And one other thing Andy, the distributor you had in that there engine was definitely the right one, it was built up properly and I know you set up the timing properly. So, you know....

[classicswede]

Well that answers that one.

Does anyone remember what brand the pistons were so we all know which ones to avoid?

[woodman]

Originally Posted by swedishandgerman

Oh! And one other thing Andy, the distributor you had in that there engine was definitely the right one, it was built up properly and I know you set up the timing properly. So, you know....

Actually Adam, the dizzy you fixed up for me has only been run in the replacement engine, which is still on the set of points you supplied, and still starts on first turn in all weathers, after about 15,000 miles....

[woodman]

Originally Posted by classicswede

Well that answers that one.

Does anyone remember what brand the pistons were so we all know which ones to avoid?

Sorry no, I guess Simon Brookhouse would know though.

[arcturus]

Hi, I know from the last time I had the head off that mine suffers from recession. Two solutions, first try to find someone reliable who would fit hardened seats + new exhaust valves.(not easy here in the Algarve)
second buy a n exchange head with hardened seats and possibly a phase 1 polished ports etc.
If I elect to go the second rout who would be the best supplier to go for and at what approximate cost?

[Sam Glover]

Thanks for all this input.

My working conclusion: defective pistons with possible exacerbation.

To rule out a few things: The bores don’t have a wear lip at the top. They’re of standard size and still show factory honing marks. The pistons are marked as standard and (slightly unscientific) measurement – plus waggling them around on the bores without rings fitted – suggests they’re the right size. There’s no evidence of block-decking or head-skimming.

Pertinent background information: I’ve only owned the ‘Amazon’ for 3000 miles. When I bought it, it was wrong in all manner of ways. It had incorrect needles in its twin SUs (too lean at mid-range; too rich at full load), a programmable distributor set to give practically no advance and a seized thermostat (plus a recently-fitted electric fan, suggesting that somebody might’ve been haplessly fighting an overheating issue). So in the previous c15,000 miles since the engine rebuild, it may well have suffered timing- and heat-related torment.

The thing is, I reckon 80% of classic cars are driving around quite happily with significant fuelling, ignition and cooling issues, or at least maladjustment. I’ve stripped more than 50 classic engines over the years, some of which have sustained impressive abuse. I’ve never come across a complete set of pistons cracked in this manner.

So: where can I buy pistons that match the quality of Volvo originals?