25hp engine with 30hp cylinders, but 25hp heads

[rdk_1973]

Thanks for all the kind reactions for my stolen VW. It has been restored again and it looks just like before. I do have a question about my engine. The engine had probably overheated and it was overhauled with new parts. The cylinders were worn out and needed to be replaced. Fortunately, I had good insurances so most costs were covered.

The engine runs fine, but when I got the bill of the restorer I saw something strange. It seems they have installed 30hp cylinders in my engine. The engine is a real 25hp engine (engine #1-0496108) and the heads are original 25hp VW heads as well (111-101-371). I asked the restorer and his administration states that these cylinders are installed. As you can see, these are the cylinders for a 30hp model and use a bore of 77mm instead of the 75mm bore of standard 25hp models.

Now am I wondering... Is it even possible to use 77mm cylinders on a 25hp head? How can I detect if I have the correct cylinders, without removing the entire engine again?
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VW Split Beetle (1950)

[sgmalt46]

if there marked 77 on the top of the piston . then yes they are 30 hp. you would need to open up the case and heads to fit them. im sure it's been done. totally possible.
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55 deluxe 23 window bus
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55 rag top beetle
66 beetle
71 square back (sold) ! good luck with it Henry!
46 beetle 552nd royal army service corps CCG

[franklinunes]

[rdk_1973]

Thanks for your responses. I understand that you need either to change the engine casing to make the 77mm cylinders fit or you need to modify the cylinders themself?

I am wondering if the outer diameter of the cylinders (were they are mounted to the engine and heads) themselves are the same for the 75mm and the 77mm cylinders. That would make them interchangable (which was a big deal at that time). Only the cylinder walls would be 1mm thinner to accomodate the larger pistons. Because the cylinders are held inside the engine case and heads it might be strong enough. Just a theory of mine, so please correct me if I am wrong.

These are the specs of the cylinders:

• 25hp: bore 75mm, stroke 64mm, can't find space required at cylinder head and carter
  
• 30hp: bore 77mm, stroke 64mm, space required cylinder head 84mm, space required carter 82mm.
  

That would also explain why my restorer didn't notice that he used 30hp cylinders and pistons. They say the ordered the part I mentioned in my post and they just fitted it. I am sure that the old pistons were 75mm, because my friend restored the car himself and he was 100% sure.

I will check if my restorer has the old cylinders and will measure the old outer diameters. I'ld rather not open the engine again. I was hoping the difference would be visible from the outside...

REQUEST: Does somebody with spare 25hp cylinders want to measure the outer diameters of the cylinders (where the fit the carter and heads)?
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VW Split Beetle (1950)

[usariemen]

I measure 81,8 to the head and 80 to the case at a NOS 25 hp cylinder.
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Master of my domain!

[VWCOOL]

No need to remove the head just yet... first try a scope down a plug hole..

[Zwitterkafer]

At the case end, all the 25hp cylinders I have encountered are smaller in outer diameter than 36hp. I can't see how 36hp cylinders would insert into a 25hp case without machining. I wouldn't try trimming the bottoms of 36hp cylinders to make them fit....the material is already thin enough there.
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"Criticism comes easier than Craftsmanship"
- Zeuxius, 400 BC

[rdk_1973]

Well then I might run into a dispute with my restorer. Either they installed correct 25hp cylinders or they machined the cylinders or (even worse) the case/heads.

I asked for the old cylinder and pistons, but they don't have them anymore
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VW Split Beetle (1950)

[henry roberts]

unless they were really shonky and just reused the old ones then charged the insurance company an extra $350 euro for the replacements.

[rdk_1973]

Never say never, but I know this company already for almost 15 years and they never tried something like that before. Although I rather pay $350 for my old cylinders then that they modified my case and heads...
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VW Split Beetle (1950)

[Martin Southwell]

If you look back over the many topics on Samba, you'll see that this subject has been covered many times, and I have been through the same thought processes recently with a spare 1947 engine I'm rebuilding. As a rule of thumb, the 30hp barrels generally have more fins on them, and are thinner than the 25hp ones, and if the finning on the barrels towards the head completely surrounds the studs, then that is another sign.

The bottom line is this. If you fit 30hp (77.0mm) pistons to 25hp barrels (75.0), then there is going to be very little metal left on the barrel walls, and isn't advisable. The 2nd and final oversize for 25hp pistons is 76.0mm, and really that is as far as you should go.

You can fit the 30hp barrels to your 25hp cases, but the cases will need machining out, but again this doesn't leave much metal between the studs holding the head on, and the circular space where the barrel goes through the case, and might give rise to the possibility of oil leaks. The heads will also need some attention to increase the diameters. Quite time consuming, but if your engine works OK, then at least if you need to work on the engine again in future, then you wont be chasing around looking for 25hp barrels & pistons. That's the good side, and if that is what this company have done, then I wouldn't be too upset.

In the end, rather than do any of the above on the 47 engine, I bought two sets of NOS German KS pistons, 75.5 (1st oversize) & 76.0 (2nd oversize) intended for another German car, (It's surprising how common the various dimensions are for differing vehicles) and am in the process of fitting them to the original barrels! I'll only know which set I have to use when I've taken them to the machine shop. At least this way I'm not damaging an original crankcase, or heads, but you wouldn't expect a commercial operation to go to the lengths I've gone to, otherwise they would be soon out of business!

[Zwitterkafer]

Yes, it is true that some pistons from other German cars of the era have the same 75 mm diameters, maybe even similar lengths and skirt designs. The more subtle differences that must be considered include piston pin location, offset, weight of the pistons, and the types of rings required. If the nature of the application did not matter, then there would have been more widespread sharing of piston designs between marques.
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"Criticism comes easier than Craftsmanship"
- Zeuxius, 400 BC

[rdk_1973]

Thank you for your very thorough explanation of the conversion from 25hp to 30hp cylinders. But I don't wanted to do this. I am afraid somebody else did, without me knowing it.

My car has been stolen last year and the engine stalled. It was taken apart and the cylinders had some wear and compressions wasn't good. That's why the engine was rebuild. I cannot do it myself, so I brought it to the repairshop where I go for over 15 years.

I had correct 25hp cylinders in my engine and when I got the car back it ran fine. No problem. But on the bill of the engine repair I found a 30hp cylinder+piston set (around $400). The shop that repaired the car said they just fitted them, but that isn't possible if the car had correct 25hp cylinders before.

So there is something wrong and there can be several options:

• I didn't have 25hp cylinders, but the engine had been changed to 30hp before. But do regular 30hp cylinders fit a modified engine without adapting them?
  
• They had anoter 25hp cylinder+piston set on stock and installed it, but billed me with a 30hp set.
  
• They installed the old 25hp cylinders back again and charged me with a new set.
  
• They modified the cylinders or case/heads to fit the 30hp cylinders.
  

I need to be certain what has been installed. Does anyone have a picture of a 25hp cylinder or can count the number of fins on it? If someone can also do it for a 30hp cylinder, then I can visually check what is currently installed. Unfortunately, I don't have pictures of the old cylinders anymore.

When I got at the repair shop last saturday for an explanation, the repairman thought it was a 30hp engine. I was surprised by this reaction, because it's a proper split-VW with a single exhaust and everything shows it's a 25hp engine.

They rebuild splits more often, so I don't know what to think. I have been at this shop for over 15 years and they have always been honest.[/list]
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VW Split Beetle (1950)

[virtanen]

Can you insert a small camera through a spark plug hole? On the top of a pistons is stamped the diameter, and you can see also if the top is concave formed.

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Mika
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[Zwitterkafer]

<X2>

I suspect that the engine was 30 hp all along, that's why the replacement 30 hp cylinders fit right in without any mods. This seems the most likely scenario, especially if your shop has lots of 25hp engine experience and is familiar with their value. I would expect them to ask your permission before machining your case and heads, making them 25hp incompatible going forward.

The previous owner is not available to confirm what size cylinders were in there to begin with?
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"Criticism comes easier than Craftsmanship"
- Zeuxius, 400 BC

[rdk_1973]

The previous owner (that rebuild the engine) is certain that he never machined the engine himself to work with 30pk cylinders. But maybe it was already done before him, but it had to be done before 1985 (that year he obtained the car).

A friend of mine has an borescope, so we will check if we can read what is on the piston. I hope it won't be as black as the piston I have here from an old engine. But the engine ran for only 400 miles, so I hope it's still readable.
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VW Split Beetle (1950)