Oil pressure relief valves don't fit in Auto Linea case.

So I am a couple of months into building my first air-cooled engine. This is a completely standard 1600 dp being built on a new Auto Linea case, the original being too far gone to reuse. It's taken months to get all the parts and machining done but so far so good. I have now completed the short block and am ready to move on to install pistons and heads. One final job before I move on and that is to fit the original oil pressure relief valves. Here's the problem. They don't fit. The internal bores of the new case are at least .4mm smaller than the pistons and the long spring piston doesn't even pass the cap threads. So will I need to get the bores reamed out or alter the pistons changed? Or am I missing something obvious?

 

I don't know about the type 1 but there are at least two different piston diameters for a Type 4. I'd avoid reaming the case if at all possible, especially now it's built.

 

Hi.
What do Auto Linea say?

 

Type 1 has a single grooved piston. I cant find any reference to various sizes for the T1. This is what I have. Both bores are approx .5mm undersized for their respective pistons. Haven't spoken with VWH yet as only just discovered the problem this morning.

 

See what they say. I wouldn't go reaming the case. Plenty of folk use the Autolineas - must be a solution.

 

OK so nothing obvious then. I will contact VWH for a solution.

 

Resist the temptation to get the reamer out! Your pistons don't fit in the bores at all?

 

One of the misfitting valves has a groove. So they probably aren't stock. Could be an EMPI set ..

Have a quiet word with any builder using Autolinea cases. Ask if you can buy a set of the oil pressure relief valves they use.

 

A quick video to show the problem.
Everything I've read so far shows the rear long spring one with a groove. I have discovered part number 113115411 is 19x16 so I can get a small front piston to fit, but I haven't found the larger grooved one at 16.5mm yet.

 

The stock pistons do not have a groove.

But the larger stock piston is 17.0 mm and the threads on the screw that holds the spring are 17.0mm (groove to groove) inner 17.8 outer( peak to peak) So the stock piston only just squeezes in the hole.



Unfortunately I seem to have lost my EMPI larger piston, only having the smaller EMPI and stock piston which are both 16mm..


Stock pistons side by side


And an EMPI piston..

 

So it looks like I have oversized pistons from my original remanufactured engine. A standard set (without the groove) should fit the new case. Unfortunately, suppliers don't seem to readily list the measurement of pistons so you'd have to be pretty clued up to know there is an oversized option. I don't know why the old engine had larger pistons. Was this an original VW option, and for what purpose? Would it explain why it used to take so long for the oil temps to get fully hot? Typically a 50-60 mile run up the M5. There seem to be a lot of heavy duty kits available but standard ones seem a bit thin on the ground. I'm wondering if I can retain the use of the original springs or are they matched to the oversized pistons? If so I could just obtain a new 16mm piston and reuse the non-grooved 16.5mm one in the other position?

 

Sounds like an explanation. Maybe they reamed out the case so they could reuse it, if the bores were scored? I'd keep your eye out for a set of originals - must be plenty around.

Do folk like VWH not sell sets? I'd avoid the "heavy duty" sets. VW didn't seem to think you needed them.

 

I checked - I think the stock size is 16 mm, e.g. CoolAir describe 16.5 mm as 0.5mm oversize. (My 17mm comes from a hacky rebuilder , VEGE, ... They would ream the piston bores because the pistons eat into the side of the bore and jam up causing high pressure spikes over time. )
So a pair of identical 16 mm pistons is what it takes according to the CoolAir blurb, I think the idea is the waisted style come from pre-1969 single relief engines according to my VW engine manual, and then after that they are not waisted.

This looks like the correct piston .
Piston:
https://www.coolairvw.co.uk/product/113115411/
Complete kit with springs..
https://www.coolairvw.co.uk/product/111115421kit/

And yes, it does take a fair amount of driving to get to full engine temperature - mine settles down after about 30-35 miles.

 

I bought a 2nd hand set of originals a few years ago from FBI or megabug.

Let me know if you want me to measure anything

 

What’s your inside leg measurements?

 

Looks like a long fitting to me, Kenneth.

Were you out with a lady last night, sir?

 

Yes, that's what I found. I thought I could reuse the 16.5 mm in the pulley end but when I trial-fitted it the spring was projecting almost 75mm out of the hole. On closer inspection, the bore is 16.5mm then a shelf and then the bore diameter is 16mm. So could that be an option for a standard 16mm with the long spring setup or alternatively a 16.5mm piston with a smaller spring? I'm going to fit a pair of new 16mm with my original springs. https://www.coolairvw.co.uk/product/113115411/
At least I can now continue with pistons and heads. Next question coming up.....

 

Your engine is 50 years old, the bores your springs are from had over sized pistons.
What makes you think the springs are original?
These simple springs can prevent your oil cooling properly if they are over-specced and there are a lot of those about.
The specs are in the manuals.
Apologies if you've measured them up already.

 

ooooh!

 

My bad description. By original I mean the engine they came out of, not that they are original VW items. Don't assume anything, I'm still researching how to do all of this. I'm just looking at spring info in Bently. My springs are unloaded length:- relief 74mm and control 32mm. Bently says 1972 on loaded length is 39mm relief and 26mm control. So my old springs are specific to the oversized piston setup. Looks like I may be able to use the 16.5mm for the control with a shorter spring. Not sure how you go about measuring loaded length but does my control spring sound correct? The relief spring is obviously too long and will need to be replaced.
Complicated this stuff, isn't it.