1972 fastback. nwe 532k

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kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 19th February 2019 - 6:16pm

But my piston size is 86.5mm, not 87mm ??

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 19th February 2019 - 6:36pm

Do I have a set of oversize pistons like here,

https://www.mecatechnic.com/en-GB/rings ... D51708.htm

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broady_6
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Re: 1972 fastback. nwe 532k

Post by broady_6 » 19th February 2019 - 6:36pm

yeah, its the bore which is 87mm, the piston is slightly smaller in order to fit inside. The exact size will be stamped on the top somewhere, its usually two decimal places.

Their were two oversizes with increases of 0.5mm each. so 86mm and 86.5mm bores
The sultan of swing

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 19th February 2019 - 6:58pm

Yep. 86.95

Odd size threw me initially as I have always stuck to stock. Never bothered with any
additional big bore kits or upgrades, or needed them.

Where do I find the wear limits for such oddities as these items :D

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broady_6
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Re: 1972 fastback. nwe 532k

Post by broady_6 » 19th February 2019 - 7:01pm

Common upgrade, considered as big as you can go without machining the block. I'll look the specs up later
The sultan of swing

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 19th February 2019 - 7:18pm

I,m out of the workshop now, so I cant check. But have my heads been flycut for this upgrade
meaning there is no return to stock with these heads. I assume thats why the flaps and thermostat
have been left out, due to some concerns with over heating with this set up.

Thanks

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937carrera
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Re: 1972 fastback. nwe 532k

Post by 937carrera » 19th February 2019 - 8:21pm

I would say that it's more like engineering from Bodgit 'n Flogit :)

There's only a 3.5% increase in capacity, so not that much additional heat on the assumption that compression ratio is unchanged - that's where heat increases occur
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 19th February 2019 - 8:55pm

Thought I read some where that the reduced barrel wall thickness gave some concerns over the ability to
cool as quick as a fuller wall thickness.

So I am left with the 1641 then. Is it a 2.2.5mm ring thickness then. Its warmer to pick your brains than run out to a cold workshop :D

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937carrera
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Re: 1972 fastback. nwe 532k

Post by 937carrera » 19th February 2019 - 9:15pm

Hmm, you're looking for a proper engineer then :)

I'll have a go, no google involved

Cooling is about transfer of heat. Heat is transferred by surface area, flow of cooling fluid over the surface, difference in temperature between the surface and the cooling fluid, the materials of construction and to a limited extent the colour of the materials (why are your central heating radiators white ?). See what I did there, talking about fluids. That means air or water :badgrin:

Heat is generated by combustion, the barrel walls act as a (very short term) heat sink until the cooling air takes the heat away. If each combustion cycle generates a bit more heat, then the additional heat will go into the barrels until a new, higher equilibrium temperature is reached, everything else being equal.

Given that the surface area of the barrel (and don't forget the surface area of the fins which aren't changing either) remains the same, and as the temperature rises the cooling fluid removes more heat, I can't see that there's much to worry about.

I'll let Broady get his heat transfer formulas and calculator out to prove me right or wrong, it should be good revison :)

As to piston rings for a 1641cc engine, I'll leave that to others, I'm a type 4 guy so I don't know much about small capacity engines :badgrin:
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 19th February 2019 - 10:01pm

Nice one, I,m impressed :D

And i never even had to leave my seat, and google free :lol:

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 20th February 2019 - 8:23am

Not knowing what if any, machining is required to install 1641 barrels into stock heads,
I am making this assumption.

Can I get stock 1600 barrels that I have , re honed to match the 1641 pistons I have ,
instead of purchasing new,cheap off the shelf 1641 barrels.

My theory being, better to use the original german stuff.

If I have to buy new, whats the best.

Is my assumption correct.

My existing 1641 barrels need to be honed, and I am not sure if I have enough meat on them all.

Thanks,
Tim

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937carrera
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Re: 1972 fastback. nwe 532k

Post by 937carrera » 20th February 2019 - 9:17am

It'll take a long long time to hone 1.5mm, (or 0.75mm all round ) you'll need to get them machined. You could well be right about new quality vs original.

Have you measured your 1641cc pistons and barrels with a mic and bore gauge to establish clearance ?

While you have the gauges out I would also compare the barrel wall thickness between OE and the 1641cc, that'll allow a comparison to be made of the OD of the barrels,back to your cooling question.

I'm in the middle of getting ready to rebuild a T25 engine, one of the bores had a groove caused by a piston ring breakage. I have honed that out and it is still well within the wear limits.

Before, as removed
Image

After - Zoomed in more, I'm sure this will be fine,but I suspect I will do a bit more work to get rid of the final marks. Completely non detectable by feel, only show up if you hold the barrel at a certain angle. I only removed a bit over 0.01mm IIRC

Image
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 20th February 2019 - 12:30pm

On reflection, I might just do better by bringing other stock 1600 barrels up to spec
by honing and fitting up these up with new rings. At leastI wont be compounding possible
cooling issues with radical honing on 1641 barrels.

I have plenty of serviceable stock 1600 barrels of good german VW lineage.

Thats the plan now methinks.

I dont think I,d live long enough to hone 1.5 from 4 barrels :lol:
not that I'd have done that at all. I live near an old school engine reconditioning
workshop. 8)

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 20th February 2019 - 12:47pm

I have had a better chance today to inspect what I have more closely. I dont believe
that it makes any sense at all in working with these barrels.
I can see lots of wasted effort on these to be honest.
Image

Image

So I think I will be sorting through my stash of pots.

But I might just measure this one before and after exercise just to familiarize
myself again with the process of whats achieveable and at what rate of honing.
Been a couple of years since my last honing exercise.

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937carrera
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Re: 1972 fastback. nwe 532k

Post by 937carrera » 20th February 2019 - 12:56pm

... and there I was thinking you came to a decision because Broady hadn't done his maths homework for you

I've been googling now, eg

https://www.thesamba.com/vw/forum/viewt ... 48&start=0

https://shoptalkforums.com/viewtopic.php?t=134258

The issue seems to be more about barrels warping than overheating. It's always an problem when someone throws together a ton of different and unmatched / ill thought out "performance mods" too, especially with replacement carbs.

Funny, my folk memory was that 1641 engines were for many the ultimate goal in the Beetle world, maybe not :roll:

Are those pictures of the 87mm barrels?

If you've got the honing tool and a bore gauge, then why not see how nice one of them looks after a couple of hours work

How thick are the barrel walls ?
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 20th February 2019 - 1:30pm

Well , I have no Faith in asking Alexa or asking Siri,....but when they put an Ask Broady on my ipod,

I,ll be a happy camper :lol: :lol:

Yep those are the barrels, and I,m gonna give one a seeing to later today.
But I reckon whats going to be needed to bring them up to spec is going to put me nearer
to the wear limit. But we will see.

I was never an officianado of the mods and upgrades on v dubs. This slamming and
narrowing of cars makes them undriveable, and I dont understand it. I prefer stock.

I have the 1641 engine because I got it very reasonable, and bought it as stock.

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 20th February 2019 - 1:31pm

Dont know the wall thickness yet.

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 20th February 2019 - 5:45pm

Wall thickness as good as I can tell with a vernier is 3.5mm.
Micrometer is sitting in a family members workshop 25 mile away.

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broady_6
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Re: 1972 fastback. nwe 532k

Post by broady_6 » 20th February 2019 - 5:55pm

I havent read all of your replies yet. But its all a myth. Theres nothing wrong with the 87mm barrels and pistons. The differences are negligible, maybe you'll take a couple of thousand miles of life off of the engine. But given the limited use the cars get these days, you're looking at the loss of year? A well built engine will be happy enough for 20 years with out much more than a gasket change.

No machining is require on 1600 heads to install the 87mm barrels and pistons as externally they are the same dimensions at 85.5s. If your head has been machine to fit them in, id suggest they didnt start life with a 1600 engine.

As long as everything is set correctly and the cooling system is working efficiently, which the flaps installed you will not need to do any modification to run the 87mm barrels. Unless you plan to be driving at 100% throttle for mile after mile.

Ive built many for people, even to go on campervans, which are much less aerodynamic and heavier. The extra "stress" has made no difference to the engines performance or durability.

If you were how ever condisidering changing the cam shaft, carbs, or any other upgrade, then things would start to get warmer.

One other note, if you do got 87mm, you may need to slightly increase the jet size, but ive often found 40 years of wear has opened the jets up just enough to compensate for the small capacity increase.

Short answer, it'll be reet.
The sultan of swing

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 20th February 2019 - 6:11pm

Nice one. You've just made Siri and Alexa redundant :D

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sparkywig
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Re: 1972 fastback. nwe 532k

Post by sparkywig » 20th February 2019 - 8:17pm

There is no machining required for 87mm (1641cc) barrels and pistons, you can refit 85.5mm standard bore without any issues.

I ran 88mm (1679cc) barrels and pistons in my old '72 bus. They're the largest you can fit without any machining.
Never had an issue with them, or the Weber twin choke carb that was another no-no, and that bus was a daily driver and did the 400 mile round trip to North Devon and Cornwall every weekend.
Don't believe all the myths and hearsay associated with VW ownership.
In 35 years of running air-cooled VWs I can honestly say the majority of the people who perpetuate these myths have no real world experience.

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937carrera
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Re: 1972 fastback. nwe 532k

Post by 937carrera » 20th February 2019 - 8:32pm

sparkywig wrote:
20th February 2019 - 8:17pm
In 35 years of running air-cooled VWs I can honestly say the majority of the people who perpetuate these myths have no real world experience.
More like no real appreciation of engineering, love the "scene" parts and simply copy / paste whatever has been posted before.

... oh hang on, what does that make us ?

Still that just leaves Kaddy to finish cleaning up his 87mm bores before deciding what build he is going to do :)
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

kaddy
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Re: 1972 fastback. nwe 532k

Post by kaddy » 20th February 2019 - 9:05pm

Still that just leaves Kaddy to finish cleaning up his 87mm bores before deciding what build he is going to do :)
[/quote]

I,m getting too long in then tooth to be getting too adventurous, I just want sedate tranquility in my life now.

Just want to finish my precious..............

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sparkywig
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Re: 1972 fastback. nwe 532k

Post by sparkywig » 20th February 2019 - 9:07pm

kaddy wrote:
20th February 2019 - 1:30pm

I was never an officianado of the mods and upgrades on v dubs. This slamming and
narrowing of cars makes them undriveable, and I dont understand it. I prefer stock.
Horses for courses, it would be boring if we all liked the same things. 🙂
All my VWs are modified, narrowed, lowered and two have stroker engines. They’re not undriveable and ride well, my bus has recorded almost 110mph around Spa, but you do need to do the complete package of suspension, steering, brakes, etc.
I do get frustrated when people follow scene trends with no mechanical appreciation.

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broady_6
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Re: 1972 fastback. nwe 532k

Post by broady_6 » 20th February 2019 - 9:23pm

sparkywig wrote:
20th February 2019 - 9:07pm
kaddy wrote:
20th February 2019 - 1:30pm

I was never an officianado of the mods and upgrades on v dubs. This slamming and
narrowing of cars makes them undriveable, and I dont understand it. I prefer stock.
Horses for courses, it would be boring if we all liked the same things. 🙂
All my VWs are modified, narrowed, lowered and two have stroker engines. They’re not undriveable and ride well, my bus has recorded almost 110mph around Spa, but you do need to do the complete package of suspension, steering, brakes, etc.
I do get frustrated when people follow scene trends with no mechanical appreciation.
Completely agree. Ive been in some semi lowered VW' and felt like ive aged 30 years in half an hour.

Then ive been in this

Image

Which rides as good as my daily driver octavia. VW largely got it right to start with, but they can be lowered, speed up, or slowed down with the same ride quality being retained. But I also appreciated a nice stock vehicle too. im neither for or against either stable. im simply pro a job done well, rather than a job done "so scene it hurts"
The sultan of swing

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