WW 81mm Big Bore Blowby

[lardawge]

Hey all,

I had a 36hp engine built by a local builder. We used the WW 81mm piston kit (probably not a great idea). On my first longish drive on the freeway, I noticed oil leaking around the oil breather (early engine with drop-in breather) and the pulley. There was quite a lot of oil.

It appears that it was caused by excessive crankcase pressure caused by the rings not seating correctly. I pulled #4 spark plug and it has oil residue on it. All others look normal.

We ended up putting a sand seal in it to stop the oil leak from the crank pulley. That turned out to help but the oil found its way past the inside of the pulley and came out around the bolt. I also installed vented valve covers... which did very little to solve the problem.

I then found an improperly installed oil vapor barrier. It was installed upside down and the very bottom drain was not open... So of course I thought I had found the issue... the motor could not vent properly. It did solve one problem, the oil filler no longer leaks.

However, it did not fully solve the issue with the rings seating which I am convinced is still causing high case pressure. I see a tiny bit of oil coming through the sand seal as well as a fair amount coming from the valve cover vents. I also still have an oily #4 spark plug.

After that long story, has anyone had issues with these pistons? I don't see many threads mentioning them being used.
Is there a good way to test for blowby?
Thoughts on next steps?
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11/2/54 L227 Strato Silver Ragtop - Soon to be L41 Black - Build Thread
1/7/55 L275 Light Beige

[oldslow]

Well you could test for compression. But you will either have low compression, or not. Either way you have to open up that side, to find what’s up, where you will find miss-aligned ring gaps, if you are lucky. You are not lucky. Get prepared for broken rings, a scored cylinder or a bent oil scraper. You can then get your builder to buy a broken set 81mm piston&cylinder and a set of rings. And hopefully they get it right this time.
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- better to drive a slow car fast than fast car slow -

[esde]

Who makes the rings that come with the Wolfsburg West pistons? What prep was done to the cylinders during assembly?
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modok wrote:
Bent cranks are silent but gather no moss. I mean, ah, something like that.

[lardawge]

[oldslow]

Rings available at Wolfsburg West
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- better to drive a slow car fast than fast car slow -

[lardawge]

[mukluk]

[lardawge]

[Bub]

I'm not sure the blowby means anything is really wrong. Hard to say what you'd consider excessive compared to the next guy. It's fairly tough to build a 36HP that you actually drive that doesn't leak a drip or two. I think it's fairly well known that big bore on a 36hp creates a lot more case pressure. The baffle helps, but I don't think it's enough if you drive it a decent amount. The volume inside a 36hp case is quite a bit less than a later one and you make the pistons bigger by just a mm or two and you're moving A LOT more air around inside.
I built a 1386 (83mm big bore) and the increase in case pressure is noticeable- open the oil cap while it's running and it's obvious. I have one nagging drip from one valve cover, not bad; just average, And I do get a little weeping from behind the crank pulley but I'm really trying to come up with a subtle vent system that looks proper.
Just some thoughts before you tear the engine down chasing rings. Mine did seem to be REAL bad for the first couple hundred miles after I built it, and way worse in cooler weather. I have 1k or so miles on it now and it seems to have subsided a bit.
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[lardawge]

[Alstrup]

Hello.
It is a known problem that nobody seems to care much about since its "an old engine" The reason is that the cylinders are not always round. Today I don´t even bother to check, I simply put the slave hone in the cylinders and give them a tour. 9 out of 10 times the cylinder jumps back & forth the first 10-15 strokes, then they calm down. The 10th cylinder needs more, maybe another 25-30 strokes to get round. Next, preparing the cylinders are often a rather overlooked chapter, but they need to be THOROUGHLY cleaned. The rings are not the best either, but it is difficult to find anything for replacement in 81 mm bore. That makes it even more important that the preparation is optimum. Lastly, install the rings dry. Lube the oil ring and the piston skirts, no more. When the time comes, start the engine and let it sit at about 2000 rpm for 10 minutes or so, then get out on the street and put some load on the rings. Spirited driving is good without ringing to peak rpm and without lugging it. After 45ish minutes drain the oil on WARM engine and start over. Again, it is important that the first 100-150 miles or so is spirited and with lots of on & off throttle. Then you are reasonably sure that you get a good result.
And no, just because its an old engine doesnt mean that it has excessive blowby per definition.

Hope this helps. And good luck.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993