cracks in pre-combustion chambers from Spec...? (2 Viewers)

[Jan-78FJ40]

PS: Jan-78FJ40 in the future try John at RADD for parts, I think that you'll be pleased with the value.

I will contact him soon for rebuilt kit and oil pump.

I ordered these things online from the supplier above fully expecting that they'll not be able to source them. I was positively surprised when the stuff actually showed up.
cheers,
good luck with your engine,
Jan

 

[Terrazzo]

I have seen many that are cracked (I don't recall seeing any used ones that were not) and most, not all, are radially in relation to the piston, those generally are not a problem.

The cracks to be concerned about are the cracks, which if they were to go all the way through, would leave a section of the pre-combustion chamber unsupported and liable to fall into the combustion chamber.

I can relate as I've had an engine lock up due to a falling pre-combustion chamber.

I have a cracked head on my 3b engine and bought a used one to replace it. The combustion chamber port hole plug (alias cups i think) are cracked in the used head but not in my original head. Unfortunately I can't get them out and don't know where to find the special tool required.
Any advise would be much appreciated
Thanks
Terry

 

[amaurer]

I have a cracked head on my 3b engine and bought a used one to replace it. The combustion chamber port hole plug (alias cups i think) are cracked in the used head but not in my original head. Unfortunately I can't get them out and don't know where to find the special tool required.
Any advise would be much appreciated
Thanks
Terry

Toyota had a puller tool that could hook into the gas opening and yank them. The rest of us use a hammer through the injector hole.

A big hammer.

 

[sodafeld1]

Jeff;

Virtually all heads that have been in place for a while will have cracks in the chambers.

I have combustion chambers here, and they can be shipped to your guy in Mammoth to arrive in a few days. For the cost of new ones, I don't think it's worth taking the risk.

As others have said, you should not install a head with cracked chambers on it. They should always get replaced if any cracks are present, and after they go in, the head needs to be lightly machined to bring the depth back into spec.

~John

It makes sense to machine the head, but wouldn't the precups get damaged? The lip on a new precup is awful thin.

 

[Radd Cruisers]

Talk about old threads... wow!

Yes, the head can be machined with the pre-cups in place, however many engine manuals specify that the pre-cup should (preferably) protrude from the surface of the head very slightly.

The edges of the pre-cups are not that thin.

I have several photos on my ecom site that show different views - select the side view image and look for yourself.

2H Pre-Combustion Chamber - Toyota 2H (pre-cup) 11106-68011

Pre-combustion chamber to suit Toyota 2H engines<br /> Stainless steel <br /> Toyota pn: <br /> 11106-68011<br />

radd-cruisers.shoplightspeed.com

~John

 

[sodafeld1]

Talk about old threads... wow!

Yes, the head can be machined with the pre-cups in place, however many engine manuals specify that the pre-cup should (preferably) protrude from the surface of the head very slightly.

The edges of the pre-cups are not that thin.

I have several photos on my ecom site that show different views - select the side view image and look for yourself.

2H Pre-Combustion Chamber - Toyota 2H (pre-cup) 11106-68011

Pre-combustion chamber to suit Toyota 2H engines<br /> Stainless steel <br /> Toyota pn: <br /> 11106-68011<br />

radd-cruisers.shoplightspeed.com

~John

Thanks John. The internal lip of the opening on the pre cup looks a bit thin to me, but you should know better than I. The corners of those openings where the lip is thinnest would be the weak spot for a crack to develop. But there would be plenty of indirect diesels happily chugging away with liitle cracks in the pre cups.

Manual says 0-0.1mm protrusion, I have 0.13mm protrusion on one of the cups on a used head. Not sure if the older machine at the cylinder head shop down the road can shave .03mm , it is not much for sure. The head surface could do with a skim, it is a bit pitted from a rust dissolve bath.
I was happy to find a 2h head without warping or cracks (visual dye test only), the cost of a new toyota head was a crazy price and I kind of give a used toyota head more credit than a new chinese head.

Funny enough manual calls for .2mm limit for warpage across the head deck which is twice the amount compared to the protrusion limit.

The core deck has been shaved a wisker too so the piston protrudes

 

[Radd Cruisers]

Thanks John. The internal lip of the opening on the pre cup looks a bit thin to me, but you should know better than I. The corners of those openings where the lip is thinnest would be the weak spot for a crack to develop. But there would be plenty of indirect diesels happily chugging away with liitle cracks in the pre cups.

Manual says 0-0.1mm protrusion, I have 0.13mm protrusion on one of the cups on a used head. Not sure if the older machine at the cylinder head shop down the road can shave .03mm , it is not much for sure. The head surface could do with a skim, it is a bit pitted from a rust dissolve bath.
I was happy to find a 2h head without warping or cracks (visual dye test only), the cost of a new toyota head was a crazy price and I kind of give a used toyota head more credit than a new chinese head.

Funny enough manual calls for .2mm limit for warpage across the head deck which is twice the amount compared to the protrusion limit.

The core deck has been shaved a wisker too so the piston protrudes

I don't think the 0.03mm would make a difference.

The pre-cups will push into the head gasket, and gets 'soaked up' in things.

Piston protrusions are something you have to be careful with. Are we talking about a parent bore or a linered engine here? Often the pistons get topped the amount the block is getting decked, or if you want to assemble things, then you can check your protrusions and then get the pistons topped (decked, shaved) to correct them so that they do not interfere (which can and does lead to hammered and then spun rod bearings).


John

 

[sodafeld1]

I don't think the 0.03mm would make a difference.

The pre-cups will push into the head gasket, and gets 'soaked up' in things.

Piston protrusions are something you have to be careful with. Are we talking about a parent bore or a linered engine here? Often the pistons get topped the amount the block is getting decked, or if you want to assemble things, then you can check your protrusions and then get the pistons topped (decked, shaved) to correct them so that they do not interfere (which can and does lead to hammered and then spun rod bearings).


John

It is parent bore. I remeasured again, this time with dial gauge mounted to a bridge, which seems to be the most consistent way of measuring compared to feeler gauges or dial gauge mounted to a swivel arm. All within spec. Also I have found, it is really worthwhile to give the precups a good whack to ensure correct seating.

Whilst I have you here, I know pics are not the best way to judge a surface, but would you consider this head requiring a skim?
I used kbs rust blast soak powder, it got rid of all rust but left the mottled pitting. Pressure blast and brass wire brush clean up then I gave it the lightest skim with a 7inch flat 600mesh lapping plate to see the high spots.

So after using the dial gauge bridge I feel a little better
The core block piston protrusion is max 0.52mm which is 0.01mm under spec. At least I am confident my pistons are not going to bang against the head.
I really appreciate you taking the time John. Also, do you routinely change over valve guides?

 

[Radd Cruisers]

The surface finish depends on whether you're going to be using an MLS or composite style head gasket, with a composite gasket tolerating a somewhat less smooth surface.

The finish is measured in something called RA (roughness average) and for an MLS gasket it needs to be fairly smooth (appears almost mirror smooth - probably close to how the pre-combustion chambers look), in the 20-30 range. A lower number is smoother than a larger number.

For a composite gasket, the range can be from 30-100 depending on the construction of the gasket you are using.

The head and block also need to be within factory spec for flatness, and they should also be finished to the same RA.

It's best to discuss surface finish with an engine machine shop as they will have the correct tools to test the RA for the gasket you are going to use.


~John

 

[sodafeld1]

The surface finish depends on whether you're going to be using an MLS or composite style head gasket, with a composite gasket tolerating a somewhat less smooth surface.

The finish is measured in something called RA (roughness average) and for an MLS gasket it needs to be fairly smooth (appears almost mirror smooth - probably close to how the pre-combustion chambers look), in the 20-30 range. A lower number is smoother than a larger number.

For a composite gasket, the range can be from 30-100 depending on the construction of the gasket you are using.

The head and block also need to be within factory spec for flatness, and they should also be finished to the same RA.

It's best to discuss surface finish with an engine machine shop as they will have the correct tools to test the RA for the gasket you are going to use.


~John

many thanks , gentleman and scholar, not many of us left