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Engine rebuild question

sunny67

sunny67

Silver Level Sponsor
My 1967 Alpine came with this extremely tired engine. It’s very hard to start, especially when cold outside. It has around 95 lbs of compression in each cylinder. This reading was made with a warmed up engine and carb removed. What’s unexpected is that the engine runs smooth, does not smoke out the exhaust, and no blow by but very little power. I’ve purchased the proper S5 cam, aluminum head, intake, and carbs to build a proper engine using a resleeved block I also acquired. My questions are: if by luck this engine has a stock bore, will these flat top pistons work with the aluminum head or will I have too high of compression to run regular gas? Also, does anyone know what the engraving on one of the pistons mean. IMG_9742.jpegIMG_9747.jpegIMG_9745.pngIMG_0107.jpeg
 
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My $.02

The Odds of being able to reuse those pistons

are about the same as winning the Power Ball.

...or any of the other High odds "games"...

DW
 
sunny67 said:
My questions are: if by luck this engine has a stock bore, will these flat top pistons work with the aluminum head or will I have too high of compression to run regular gas? Also, does anyone know what the engraving on one of the pistons mean.
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S-67,

The compression ratio is determined solely by the volume of the combustion chamber in the installed head - alloy or iron - because the same pistons were installed in both engines.

That stated, the O/E pistons should have a shallow, surface dish of about 6.9 to 7.5 c.c.

If your pistons are truly "flat tops," then they wouldn't be original. The stamped numbers you're asking about MIGHT be an oversize stamping, but between the extended photo resolution and surface deposits, I'm unable to make a guess about meaning - might just be a part number.

Two reasons I would advise against reusing those pistons:

First> in the picture which includes part of the piston wall you can see what appears to be horizontal lines where the rings were trying to be, if not, stuck to the cylinder wall. These engines have had problems with broken rings and lands, at times. I would be hesitant to reuse an unknown piston where the lands may have been stressed breaking stuck rings loose.

Second> if the piston is truly a "flat top," IIIRC, there were some inexpensive replacement pistons around years ago that didn't have a good reputation for quality and the compression height had been dropped much lower than stock decreasing the compression ratio. The only way to know is pull a piston and measure the compression height, then compare measurements with a stock piston.

BTW, you'll also need an exhaust manifold and pushrods to match the alloy head.

Hope this helps,

1770617163165.png
 
I don't know if your car is an Alpine series 5 or not but to have matters clear this engine is not an original Sunbeam Alpine series 5 engine but an engine from a an Alpine Coupe (North America only).
 
husky drvr said:
S-67,

The compression ratio is determined solely by the volume of the combustion chamber in the installed head - alloy or iron - because the same pistons were installed in both engines.

That stated, the O/E pistons should have a shallow, surface dish of about 6.9 to 7.5 c.c.

If your pistons are truly "flat tops," then they wouldn't be original. The stamped numbers you're asking about MIGHT be an oversize stamping, but between the extended photo resolution and surface deposits, I'm unable to make a guess about meaning - might just be a part number.

Two reasons I would advise against reusing those pistons:

First> in the picture which includes part of the piston wall you can see what appears to be horizontal lines where the rings were trying to be, if not, stuck to the cylinder wall. These engines have had problems with broken rings and lands, at times. I would be hesitant to reuse an unknown piston where the lands may have been stressed breaking stuck rings loose.

Second> if the piston is truly a "flat top," IIIRC, there were some inexpensive replacement pistons around years ago that didn't have a good reputation for quality and the compression height had been dropped much lower than stock decreasing the compression ratio. The only way to know is pull a piston and measure the compression height, then compare measurements with a stock piston.

BTW, you'll also need an exhaust manifold and pushrods to match the alloy head.

Hope this helps,

View attachment 37544
Click to expand...
Thanks. I failed to mention that I have an exhaust manifold and exhaust system. I didn’t know I’ll need push rods. Thanks.
 
Shannon Boal said:
I would want to test a bit further. Using a source of compressed air and a leak-down tester should find any leakage causing that very low compression. https://www.harborfreight.com/search?q=cylinder leak down tester A camshaft off a tooth or two will give low power and low compression. If rings were that far gone, I would expect a cloud of blue smoke!
Click to expand...
Good info. Thanks. It’s never made sense to me how it could run so smoothly and smoke free at such low pressure. Valve timing is a possibility I hadn’t thought.
 
Here’s pictures of the re-sleeved block I mentioned. Each cylinder measures right at 3.201”. Obviously it needs some prep due to sitting around a few years but as near as I can tell, it’s in pretty good shape. Comments welcome.
 

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Nothing wrong with a sleeved block. Had one that was porous and would produce steam
into the cylinder. Sleeving solved that issue . Done a few years ago and car is still running very well.
 
From This distance, it looks like the

#1 hole is sleeved, with an incomplete job.

The rest appear to have some use.

Sleeving just one hole could

distort the block.

Check the other holes for round.

And it looks like the sleeve is

proud of the deck, usual.

A deck job is needed.

...as well as a finish hone?

DW
 
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alpine_64 said:
You have a sleeved block or it was re-bored? It would be quite unusual to sleeve a Rootes motor...
Click to expand...
Just had my1725 rebored & sleeved in order to accomodate regular size pistons. I was under the impression that by sleeving an engine you will get increased performance. Read something where Ford 302 V8 had improved compression by installing steel sleeves. Anyways, they are in my block now. Had to rebore engine considerably due to condition of chambers with sleeves reducing size of pistons required. Will find out in month or so, exciting about getting SV back !
 
My 1725 is sleeved and I have +.040 pistons. I have two summers on that engine now and it runs great.
 
Rodney Shelast said:
Just had my1725 rebored & sleeved in order to accomodate regular size pistons. I was under the impression that by sleeving an engine you will get increased performance. Read something where Ford 302 V8 had improved compression by installing steel sleeves. Anyways, they are in my block now. Had to rebore engine considerably due to condition of chambers with sleeves reducing size of pistons required. Will find out in month or so, exciting about getting SV back !
Click to expand...
I can't see why sleeving a block would do anything to compression . Compression is the ratio of space between the lowest point of stroke and highest in volume. The sleeve can allow you to maintain a smaller bore rather than an overbore... but the sleeve isn't offering any performance
 
Are you sure that you don't just have a low compression engine from one of the other Rootes cars fitted into your Alpine? They made some LC engines for countries when petrol was very poor quality. That doesn't look like a standard Alpine engine to me.
Tim R
 
Tim R said:
That doesn't look like a standard Alpine engine to me.
Tim R
Click to expand...

Tim,

It's not a series Alpine engine. The photo of the block serial number (post #1) indicates a later Alpine coupe engine.

The top of engine photo shows an iron head with single CD 150 Z-S carb - proper fitting for the Alpine coupe.

The block pad isn't stamped "LC" which it should NOT be for the North American market.

The OP states the pistons are "flattops." I can't dispute his statement, but I'm not sure from his pics, either.

If "flattops" are installed they aren't original equipment.

Barring a lucky guess, remotely diagnosing this issue will be challenging.

Hope this helps,
 
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