948 Build

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Hurtzberg
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948 Build

Post by Hurtzberg »

Hi Guys ,

I'm taking apart an old engine that Countryboy gave me.

It's actually fairly good condition inside from what I can see so I might stop dismantling it more than needed.

The head, sump and timing cover have all been removed.

Where is the cam marked so I can see if it is special? Do I have to remove the timing gear to see the end of it or should it be numbered along the body somewhere?

Thanks, Andrew.
Last edited by Hurtzberg on Tue Oct 13, 2015 2:11 pm, edited 1 time in total.
Andrew

1957 A35
Dave Clark
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Re: Camshaft identification

Post by Dave Clark »

You will need to remove the timing gear and the engine backplate so that you can withdraw the camshaft to the rear, having also removed all the cam followers.The base of the cam followers are a good indication of what you may expect to find in terms of condition.

Identifying the camshaft may be possible once you have removed it and checked various specs.

Google is your helpmate there, but I somehow doubt that it is very special.

If you bring it to the TVG meeting next Tuesday I will see what I can do.
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Re: Camshaft identification

Post by gazza82 »

Dave, don't you mean 'remove to front'?
"If you're driving on the edge ... you're leaving too much room!"

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Re: Camshaft identification

Post by Hurtzberg »

Thanks Guys, I'll dig out my manual. I was hoping to be able to read an id on it somewhere rather than measuring lobes etc.

Dave, this is a 948, It had a tired but interesting head that you looked at during the bbq. It also has stuck (now freed) flat top 030 hepolite Pistons so someone did love it at some point.

Can't afford the 1275 so thinking I can learn about engines on this one and if I can make a fruity little 948 (I guess it is actually about 972 now) to enjoy until I get a 1275 then all the better. So spending a little money on a reasonable cam isn't out of the question.

Thanks.
Andrew

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Re: Camshaft identification

Post by earthhist »

Hurtzberg wrote:
Can't afford the 1275 so thinking I can learn about engines on this one and if I can make a fruity little 948 (I guess it is actually about 972 now) to enjoy until I get a 1275 then all the better. So spending a little money on a reasonable cam isn't out of the question.
You can get a lot of fun on the road out of an A35 with a tuned 948cc engine, and keep your licence at the same time. Out and out speed isn't everything.
Richard Johnston, Plymtree Devon, formerly A30/A35 Club Technical Officer and President
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Re: Camshaft identification

Post by gazza82 »

If you were to treat it like a Mini 998cc engine, the specs you are looking for will be similar.

You could probably go from 34 to around 60 bhp ...
"If you're driving on the edge ... you're leaving too much room!"

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Re: 948 Engine build up

Post by Hurtzberg »

Sounds good to me Richard and Gazza.

I've enjoyed small engines in the past. As long as they are happy to give what they have, they are a lot of fun.

My current engine drives like a modern diesel. By that, I mean that it feels torquey and is an easy drive in slow traffic and that you must have loads of power in reserve as you're only using a small amount of throttle. but when you put your foot down, you find you were already using 90% of the performance.

With this new engine, I'd love to have the same low down behaviour but also a nice reward for when I'm in the mood for high revs and full throttle - that's why I thought a slightly hotter than standard cam could help.

It's a 948 from a Midget (I think) so should already have a reasonable improvement over standard but I don't have the matching twin carbs or a decent exhaust yet. I do have an SU somewhere but I think it is a single 1 1/4
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Re: Camshaft identification

Post by gazza82 »

Does it have any casting numbers on the head? It doesn't look like there is a lot of difference between an A35 head and a Sprite one, but some from a Mini might make it breath better with slightly large valves. The ones with large Combustion Chamber CCs would probably have had flat tip pistons, so a bit will need to be skimmed off to compensate for the dished pistons, etc.

This is "borrowed" from a table compiled by Keith Calver (known A-series tuner) ... and I've tried to make it line up to make it readable ... otherwise you can see it at http://www.calverst.com/articles/ch-cyl ... _%20no.htm

  • Casting.....Inlet................Exhaust..........CC......Fitment
  • 2A628......1.0625"/26.99......1.00"/25.4......24.5......850, 998 Mini & 948 Sprite
  • 2A629......1.0625"/26.99......1.00"/25.4......24.5......948, A35 & Morris Minor
  • 12A1456....1.0625"/26.99......1.00"/25.4......24.5......850, 998 Mini & 948 Sprite
  • 12G202......1.156"/29.36......1.00"/25.4......26.1......997 Cooper, Austin 1100 Mk ?
  • CAM4180....1.0625"/26.99......1.00"/25.4......25.5......998 Mini - A+ (1980-on) and lead free
  • 12G206......1.218"/30.93......1.00"/25.4......28.3......Early 998 Cooper, MG1100
  • 12G295......1.218"/30.93......1.00"/25.4......28.3......998 Cooper, MG1100
Just remember though, those better Mini heads are probably getting rarer and you will be up against Mini owners in any auctions! ... Although do check the wording carefully as I found a guy selling a 12G202 head as a 1275 one a year ago ... it would never have worked .. but he was adamant it would have ... :roll:

But as the parts for most are still available if the head is suitable, the larger valves could be fitted with a bit or engineering work (and go unleaded on the exhausts at the same time)
"If you're driving on the edge ... you're leaving too much room!"

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Re: Camshaft identification

Post by Hurtzberg »

It's a small bore 12a185 . Not to be confused with the very large valved Cooper head of the exact same casting number.
Its inlet and ex are roughly the same as a 12g295 when I measured them. Mr Clark took a look and pronounced it knackered.

Dave. The cam is out now but in not sure I'll make it tomorrow night as my lovely new born might take up all my time.

I didn't have a tool for the cam nut and it was already chewed up so will be a pig to remove. I have the cam with the timing wheel on the end.

Cheers.
Andrew

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Re: Camshaft identification

Post by earthhist »

The original setup was intended for economic family motoring in an era when the average motorist travelled at 35-40mph out of town - hence the concentration on low end tractability.

As has been indicated the 948cc engine can be modded like a 998cc mini. The 948cc engines are pretty tough and will cope with very high rpm compared with standard which is limited by valve bounce and breathing restrictions imposed by the standard porting, combustion chamber shape and carburettor. Up to 7000 is readily and safely achievable with suitable valve gear, breathing modifications and the right carburettor - though obviously the harder you use an engine the shorter its life.
Richard Johnston, Plymtree Devon, formerly A30/A35 Club Technical Officer and President
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Re: 948 Build

Post by Hurtzberg »

Thanks for the encouragement guys.

When I took the camshaft out last night, a piece of metal came out of the end. I'm 99% sure it is part of the oil pump and might explain why the engine was replaced. Eg, Sudden unexplained Oil Pressure issue as the pump wasn't working.

Anyway, it looks like the head that I have is the 948 friendly 24.5cc It also has dual valve springs so should help with the valve bounce.

In the near future:
1. Try to revive the cylinder head
2. Fit this and my 1 1/4 SU onto my current 948
3. Check if the other distributor has less play than the current one and fit if so.

Both engines need the seals renewed and the current one needs Rings. So I'll consider swapping the spare engine instead as it has + 030 flat tops which should increase the performance a little more, assuming these aren't knackered.
Andrew

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Re: 948 Build

Post by gazza82 »

According to my Haynes, that head looks like being a Midget I/Sprite II head (double-valve springs). The standard engine was rated at a CR of 9.0:1 if Haynes was right that was with flat topped, four-ring pistons.

I've read that a CR of around 9.75:1 is the best for today's higher octane unleaded fuels (V-Power, etc).

While I was planning my engine I used the calculator to check the CR wasn't too high:

http://www.csgnetwork.com/compcalc.html

Dimensions from my Autobook manual:

If the block is a 948cc Midget Mk II and still has an engine no it should start 9CG. Standard bore 2.478"/62.94mm, stroke 3.0"/76.2mm.

Pistons will have clamped gudgeon pins and solid skirt pistons (no slots up the sides).

I think the standard cam had a pin across the end that fitted into a slot in the oil pump drive.

You should also find you have three cam bearings in the block (A35 only had front one).
"If you're driving on the edge ... you're leaving too much room!"

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Re: 948 Build

Post by Dave Clark »

OK Andrew, I had packed measuring gear etc in case you did come, but family comes first.

Just check the width of the cam lobes. If they are 3/8" then it is an early 803/948 cam and they are pretty well all the same. If they are 1/2" wide then we need to look at lift figures and any markings to see what it is. The type of oil pump drive can also be an indicator, especially if it is non-standard.
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Re: 948 Build

Post by Hurtzberg »

Update
Took two of the pistons out during my lunch break today to see how they look:

Image

Image

Image

Not sure how I test if the rings are any good - Dave did give me a brief overview at the pub but time has past since then! I can tell you they are not broken up but that's all I know.

The other thing I noticed is that the pistons are fairly hard to move on the rods. Have no frame of reference as to how stiff they should be but I'd need to use two hands to move the piston on the gudgeon pin

Is that normal?

Thanks, Andrew.
Andrew

1957 A35
Hurtzberg
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Re: 948 Build

Post by Hurtzberg »

Took out the other two pistons and they do move easily on their gudgeon pins so I guess the first two are a little corroded. I'll take them apart and see.

Noticed the crank has notches taken out of it in places , I'll try to take a picture tomorrow.
Andrew

1957 A35
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