Piston Broke

[Bilbo]

This post is not intended to lay blame at anyone´s door, but I thought I would mention it in case anyone else suffers the same problem.

When I had my engine rebuilt, the head gasket started popping after about 300 miles and was replaced by the guy who rebuilt the engine. However it still had a knocking noise and I asked Will Burrows to take a look at it.

He concluded that I had been fitted with standard HD 1200 barrels and pistons, but with my original 883 heads.

Apparently the standard pistons have a crown 1/2mm too high for standard 883 heads and were hitting the head, causing the knocking noise.

This will also have caused the head gasket to start to blow and the head bolts to appear to have not been tightened down correctly.

He has ordered conversion pistons from WestCo which apparently have the correct crown height.

Although this is annoying and I will attempt to recover some of the cost from the builder, I am glad that he appears to have found the source of the problem. It is still at Will Burrows, so I will have more info when I see the result, hopefully some time next week.

Bilbo

[Limey_Dave]

Sorry to hear this Phil,I can imagine how sick you must feel.
Maybe as I'm not doing this stuff every day,I'm over carefull.
I always wind the bolts in without washers and if they bottom,check the gap is thiner than the washer.
When mixing and matching parts,always measure the pop up.

[grbrown]

Its quite normal to convert an 883 by fitting bigger barrels with the original heads. Suggests the original bloke hadn't a clue what he was doing.

[banquo]

So what's the normal way of ensuring the crowns don't foul the heads?
Is it necessary to use Wiseco pistons or similar, or a different head gasket to increase clearance, or what...?

[robbiemac]

Wiseco's or dremel out some material from the 883 heads. There is a procedure and a template to check how much material to remove.

The pistons that come with the HD conversion kit are a fit and ride scenario.
Least chance of error.

[girlyglide]

Wiseco conversion pistons are a straight forward fit for 883 models - it's what they were designed for; just rebore and fit.

Robbie is correct, the original conversion kit produced by "I can't remember who" back in the 1980's came with a little template to use to reprofile the combustion chamber on 883 heads. Made the job a bit of an arse. Wiseco got it right with no messing piston kits.

1200 H-D pistons with 883 heads will not work. Swap a complete 1200 top end and no problems. One case where mix and match won't work.

[grbrown]

Originally Posted by banquo

So what's the normal way of ensuring the crowns don't foul the heads?

Use the correct pistons! Wiseco and possibly others make matching big pistons for use with 883 heads.

It ain't exactly rocket science. Big BSA twins were built in the 60s with B44 (441 cc) pistons under 650cc heads, even 500cc heads, to deliberately create a wide squish band, which promotes swirl and other beneficial combustion characteristics, as the pistons get close to the heads.

Current racing car engines even bounce the pistons off the heads on the exhaust stroke, using the squish band, to reduce power losses (under compression the pistons don't quite hit the heads). Possible a step too far with a Harley!

[banquo]

Useful stuff to add to the memory banks!
So, to summarise, both Harley and Wiseco do specially shaped pistons to match the 883 heads, specifically for this conversion, but the heads need to be relieved if stock 1200 pistons are used.
Good to know.

[Phil]

I know you don`t want to hear this Phil....

Have your man take a GOOD look at the tolerances of the rods when apart. That lower end will have taken a hell of a beating from the pistons hitting the heads.

The lesson of this of course is.....Make sure you have somebody that knows what the hell they are doing work on your stuff.

Anybody that had half a clue & was in the Harley Dealer or Indy business would have know not to do that.

Hope you get back on the road soon.

[Rubianroaddog]

Hey Bilbo,
Would be nice to know which muppet did this job for you. I have considered modding my 883, wouldn't want to to the same guy.
Cheers
Mick