Cylindry 92mm -tolerancje

Cześć,

Rozbudowywuję właśnie swojego 1600 do 1800, nowe cylinderki i wałek SCATa.

No i nie bardzo mam się gdzie dopytac o właściwe tolerancje wyfrezowania otworów w bloku

Ktoś może wie (a Chris na pewno -jak sądzę) jakie sa poprawne tolerancje pasowania cylinder -blok i cylinder -głowica?

W moim starym 1600 było tak;

otwór w bloku -90,0mm a zewnetrzna częśc cylindra -89,7mm
głowica -94,0mm a zewnetrzna częśc cylindra -93,7

no to wychodzi 0,3mm luzu.

Nowy zestaw MAHLE 92mm:
cylinder dół zewnątrz -95,9
cylinder góra zewnątrz -97,6

Czy mam dać średnice otworów większą o 0,3mm i powinno być OK?

pozdrawia

K

Z tego co mam zapisane to tolerancja jest 0.2mm
A rozwiert mialby byc ogolnie 98 mm z glowicy i 96 mm w bloku. O ile to w glowicy sie zgadza na tyle na ile moge zmierzyc moja suwmiarka bo taka rozwiercona glowice pod reka wlasnie mam, to to w bloku jakos takos ciasne sie wydaje...poczekajmy na Chrisa

Nie pamiętam wymiaru luzu ale cylinder w blok wchodził z lekkim oporem jak pamietam ale bez używania narzędzi no i najważaniejsze żeby były zrobione osiowo

Zobaczcie co dostałem od Amerykańców:
"The basic rule is to allow .0015" of clearance per inch of OD. That
is the MINIMUM. Typical clearance for a properly built VW aircraft
engine usually runs .006 to .008.
The figure you've cited (0.3mm) is what you can expect to find on a
MASS PRODUCED engine, in which provision is made for the stack-up
errors in the jugs. Custom built engines typically use the ACTUAL
measurements of the jugs and apply the rule mentioned above."

Czyli zakres tolerancji rozwiertu generalnie pokrywa się z tym co pisze qubek. 0.008' =0.20mm.

Mój silniczek bedzie pracował "nietypowo" -bo ok 2800 max 3200-3400 rpm, stad większość "tuningowych" operacji odnosi sie raczej do zwiekszenia jego trwałości niz podniesienia mocy.

Głównie poprzez modyfikacje oryginalnego systemu olejowego w bloku, szklanek i klawiatury -tak by dostarczyć do głowic jak najwiecej oleju

BTW - mogę Wam cos o tym napisać, rzucić jakiś zdjęcia - wiekszość operacji jest technologicznie prostacka i prawie każdy z Was może się pokusić o zwiększenie trwałości własnego silnika.

Wiekszość dostępnych materiałów mówi o zwiększaniu mocy, gaźnikach, wykorbionych bardziej wałach, etc - a mało gdzie mozna przeczytać o poprawianiu błedów konstrukcyjnych tego silnika.

pzdrw

K

Po prostu on nie ma zbyt wielu bledow w tym wzgledzie
Daj te materialy, jesli mozesz, ciekaw jestem o co chodzi.
To ma byc do samolotu?
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OK, doczytalem w profilu.
Kiedys, pamietam, rozmawialem z jednym lotnikiem, mowil ze zaczelo mu w garbowym silniku mocy brakowac. Ale fakt ze rasowanie silnika pod tym katem jest kwestia dosc specyficzna, choc bez przesady.

I have run 92 piston and cylinders in my car . I had a set in my car when I was 18 and then again a few years later in a stroker engine. Neither set lasted more than 30,000 kms.The first set was an NPR not Mahle set, but the second was Mahle. I drove every engine hard to check their life under extreme conditions and most people using the same combinations normally would have better results.They just started to fall apart as I was driving. I worked in a VW engine building company in England and my car was the test-bed for any and everything. I would never use them in an aircraft. You say so much about making an aircooled T1 live, most, but not all of which is true, and then go and use these cylinders. In a car, if they fail, you can pull over and call for help. In something flying, this is not an option. Use a 90.5 piston and cylinder set- it uses the same size hole in the head and case and will last longer. Call your supplier and ask him to change them. The extra 1.5 mm does make a difference. If you decide to keep them, check them regularly, which I am sure you do with your engines anyway. Check them for roundness, seal to the head and fine cracks where they go into the head. If you see sparks coming out of your exhaust it will be bits of cylinders and/or piston. Check the rings for sealing and the ringlands as well as the edges of the piston crown for chips. What fuel do you run is these? This applies to ring gap setting and the life of the piston/cylinders. If alcohol then you have fewer problems that are heat related, but with building alcohol engines comes other problems.
If you have the money, I would strongly recommend a set of Nikasil barrels for your application. They are much lighter, cool better and are indestructable (almost), but the full set of pistons, cylinders and head studs is about $2000

Chris,
All my opinion is based on common knowledge -but regarding to flying VWs only. Few of them can be interesting for other VW people -I hope.

I'm not as experienced as you, and I not invented any modyfications.
All are from US fellows who flew thousands VW during last 50 years.
This is a something different from typically race, or even street, engine.
Look - it have max 3400-3600rpm on take-off and spend rest of life time in 2800-3200rpm range... Typical is few minutes of max rpm and one-two hours on constant cruise rpm's.
You are absolutely right with 90,5mm jugs, it is the best combination for sure - but is to small for us a little bit. We know it as "Liberty" engine, many people flew this -on single person planes.

The racer's choice are 94's -but we mainly prefer 92mm. ((kontakt usunięty) or at yahoo group ->AirVW.)
The big difference between pilots and racers is - we have a lot of instruments here. CHT, EGT, manifold pressure, fuel pressure, oil pressure are typical for each engine -it can help keep the engine in good condition. We never exceed parameters. Flying VWs have about 600-1000hrs of life time -depends of quality of workmanship and design.

About compression -we used about 1:8 depends on requested durability. The car 95 fuel is preferred -but of course many people use AvGas 100LL with bigger CR and different ignition timing.

We have some manuals for flying conversions -there are many solutions "how to", I will try to keep (as best as I can) any clearances and gaps.

Nikasils... of course I know it. Never seen in flying VW -due to cost probably.
The another typical small aviation engine: Rotax 912 use it as well, but cost of Nickies + engine + reduction drive = cost of Rotax 912 from second hand...

Chris - which my statements about T1 are not true? I'm really interesting in your opinion -because you are one of best VW guys here.

regards

Kuba

PS Sorry for poor english...

First of all I must say that I have had limited experience in aircraft engines ( even though my father was, in his early days, an aircraft engineer- mainly Spitfires and early jets etc.) and all of what I had and have to say is based on street and race car experience.

I had a quick look at the gpasc site. They say that they use both 92 and 94mm pistons. Some use long stroke cranks. I suppose that the low rpm combined with the low power outputs, low compression and the regular servicing and instrumentation makes the choice of 92mm cylinders possible, but I am still not completly convinced as there was no information on that page as to the pros and cons of using that size. Those liquid cooled heads look great, though. I can see an advantage in using 92s over 90.5s in that you have a larger area to play with when using 42x37 valves (unshrouding), which promotes flow through the heads. This would also apply to the larger 94s, of course, which I believe to be the best size compared to expenditure and lifespan.When trying to make power is more important than long life then why not use 92s. I just do not feel that the small difference is worth the dramatic reduction in lifespan. Also, if you are using the watercooled heads then most of the points I have listed regarding the negative aspects of 92s are not at all important any more.
I also feel that the point about cases ( if I understood correctly ) is not correct. We have always tried to use good used AS21 cases in preference to a used AS41. They just seem to hold their dimensions better over time in highly stressed engines. As to welding up behind nuber 3 - this is a large area, both deep and wide. The welding would need to done carefully because of the heat build-up. I would not recommend this in all but the very largest and highly stressed engines.
Thanks for the kind words about me
As always there are many possible combinations and small differences in the choice of parts and assembly can make a huge difference to the end result. If what you and other flyers are doing and have been doing works well for you, then congratulations. I

Chris,

Aeroconversion... This is still same engine, but tuned for maximum torque on low rpm. (The best rpm for typical propellers are ab. 2200-2400rpm, smaller ones will work on 3600 with reduced eficiency) Another "strange" issue is fact -so almost all flying VWs have a propeller on pulley end. Our main problem is with quite poor durability of stock cranshaft -this end of engine was never designed for pulling something more than fan, and have a deep key hole... cracks starts here very often.

I took this 69stroke x 92bore combination after few weks of questioning another VW owners. It was really long story.
Know good opinion about 94mm from your www and from another places (aircooled.net for example), but when I just put one 94 on case... I didn't believed in this. And few people scared me about cracks in case.
Usually peoples have 1834 or 2180cc.

Regarding bigger valves with 94:
One of my correspondents made bigger valves on his 1915cc (69strokex94bore, special cam) - and get just ab. ~50 rpms more. Valves are not big limitations around 3000rpm. The situation changes with propeller reduction drive and when engine turn around 4400rpm.

About AS21/41 issues - I sent another post with genuine text from my source.
I'm not argue here. Never seen AS21, never builded any engine with it.

About welding around #3 - My sources want it... if bore is bigger than 88mm and stroke than stock 69mm. For example - GPASC manual.

Chris -I've very important question to you:
I'm ready to milling case for 92mm, How and how deep?
The genuine case have ab. 31mm between top (sealing surface) and kind of shelf bellow in cylinder hole. The new 92s are 6,7mm shorter here and have shorter piston.
Two option possibly here:

1. I will keep genuine 31 mm deep, and bore for 92s with correct clearances

2. I will bore only to deep need by cylinder (my spigot part have ab 17,5mm, previous cylinder 85,5 had 24,3mm) -it will something like step-bore

How you think?

regards

K