block identification

[dudload]

hi all,

following on from my other thread on issues with the head on my 66 traveller - i bit the bullet and bought a new reconditioned 1098 head.

However, when removing the head (the engine is a Gold seal with 8G stamped on the block), I only just realised that it doesn't have a temp sender hole by the thermo and the stamping on the head confirms it as a 948. Very curious considering the date of the car, and makes me worried that the gold seal new engine replaced a 1098 with a 948!

Moving on to block identification, it has 12A497 stamped in the block below the tappet inspection chests, and theres no sign of 950 being stamped to the front of the engine, nor a riveted panel with 1000 on (although i can see what looks like a rivet in the right place).

Main question is, is there any conclusive way i can check whether the block is 1098 or 948? Hoping to get a nice boost from this when i fire it up (waiting on the temp sender blanking being delivered) if it is a 1098 block, but worried ive just installed the wrong head on a 948!

[oliver90owner]

Measure the bore and/or stroke?

[geoberni]

Have a look at this topic.
We had quite a lot of chat about Block and Head Numbers because I had engine ID issues.
You'll see that Philthehill had the answers.
viewtopic.php?f=4&t=67378&hilit=engine+ ... 20#p642668

Looks like you can breath a sigh of relief

[dudload]

Measure the bore and/or stroke?

Unfortunately the new head is already on, so that's not an (, easy) option anymore. Only realised when I was boxing the old head up to send back!

[dudload]

Have a look at this topic.
We had quite a lot of chat about Block and Head Numbers because I had engine ID issues.
You'll see that Philthehill had the answers.
viewtopic.php?f=4&t=67378&hilit=engine+ ... 20#p642668

Looks like you can breath a sigh of relief

Thanks mate. My only small worry is that from other posts it appears that some blocks could be 948 even without the 950 stamped on side?

In other, more general questions, why on earth would BMC pair the wrong head and block combo for a gold seal?

[geoberni]

So as I understand it, you have a 1098 Block (12A497 )
But

it doesn't have a temp sender hole by the thermo and the stamping on the head confirms it as a 948.

So perhaps someone has worked on it since it was fitted and replaced the head, but repainted it gold to match?

What head number has it got?
Perhaps it is a rare one.... just guessing here...

[philthehill]

The block is a 1098cc item if the casting number is 12A497. The casting number is the important number not the 950 or lack of 950 on the block.
The head is a completely different issue. The 1098cc head should have a 12G202 casting number. What casting number does it have?
Considering the age of the engine/head anything could have happened to the engine assy.

[dudload]

good news - thanks all. i'll take a photo of the head stamping, but don't think it's rare as i came up straight away as a 948 head when i searched on here.

assume i should expect a bit of a performance boost when the new head goes on?

[philthehill]

Do not expect any significant increase in performance by just fitting a standard 12G202 head to a standard 1098cc engine.

[dudload]

Just checked and cylinder head taken off is 2a628

[philthehill]

The 2A628 (2A629) head was fitted to the 803cc and 948cc 'A' Series engine.

Note: The casting numbers do not always match the part numbers. BMC had a habit of making the casting numbers one digit higher i.e. 2A628 ditto 2A629.

[oliver90owner]

It appears you have a reduced compression ratio but larger inlet valves.

What head gasket are you using? I’m mildly surprised that the rockers are properly aligned.

[dudload]

I've used a standard 1098 gasket to fit the new 1098 head. I'm not sure why the rocker wouldn't line up, I thought it was the same rocker for all OHV engines?

There was a significant amount of clearance adjustment required, the valves on the new heads don't sit as 'high' as on the old head.

On compression, I would assume that as it's a 1098 block this won't be an issue as everything now correctly married up?

[philthehill]

The rockers will be either forged or pressed steel. Both serve the same purpose and the fit is identical.
If you have the adjuster screws with the hole down the centre I would advise that you change the adjuster screws to the solid type with no hole. The adjusters with the hole down the centre have been known to break at the waisting.
The height of the head is the same at 2.75" but there can be a variation in the height of the valve stem top above the head.
Fit the top hat type seals to the inlet valve guides. No need for seals on the exhaust valve guides. The exhaust valves need all the lubrication they can get as unleaded fuel is dry in that it has little lubricant qualities. If fitting top hat seals it is best to use the guides with the top hat seal retaining groove.

[JOWETTJAVELIN]

I am sure I've read on this forum many times that if you're fitting a 1098 head to a 948 block, the head should be skimmed by a certain amount.

[dudload]

I think it's been confirmed that my block is a 1098 though, so I've put everything back as it should be.

[philthehill]

The combustion chamber difference between a 948cc head at 24.5cc and a 1098cc head at 26.1cc is 1.6cc which is hardly worth the expense of having the head skimmed. If the head was to be skimmed to get the combustion chamber back to 24.5cc it would only need a 0.010" skim at most.
The better porting and slightly larger valve sizes would easily make up for the difference in combustion chamber size.
The 12g295 head at 28.3cc combustion chamber is the one that needs to be skimmed by 0.060" to get the compression ratio right.

[oliver90owner]

Oops. I wrote earlier ‘smaller inlet valves’. It will be larger inlet valves with the 202 head. I’ll try to correct my earlier post.

On another track - PTH will likely know - are there different pistons (with deeper, or more shallow, dishes in the piston crowns) for the 1100 blocks?

[dudload]

i think they are, yes. when re-installing the rocker assembly moving from the 948 head, i had to tighten up the adjusting screws to get to 12 and 15 thou on the inlet and exhaust valves accordingly. also had differing circlips - 948 had split pin type whilst 1098 has small circlips as far as i could tell.

Phil - on the new 1098 head, was bought reconditioned from ESM, so look to have top hat seals on every valve. might not be the best for the exhaust, but my old head seemed to be leaking alot of oil in, so should be better than that at least.

[philthehill]

Could you please clarify what you mean by split pin type and circlip type? Where do these parts fit on the engine/head?

If the top hat seals are fitted to both the inlet and exhaust valve guides I would not be concerned or rushing to remove the top hat seals from the exhaust valve guides.

The 1098cc engine could be ex factory supplied with either high or low compression pistons. The variance in compression was achieved by adjusting the volume of the piston dish. The cylinder head combustion chamber cc was the same size for both H/C & L/C engines.