Motor-tear down

[THINGONER]

So I have a 1776-stock cam and heads-mahle 90.5 pistons,dual Kadron carbs. It has never really run correctly-recently developed a major hesitation on acceleration-I thought it might be related to distributor so I messed around with that for a while and then just decided to tear it down since there has always been evidence of oil in the intake. Pulled heads a fair amount of carbon on pistons and heads. There were 2 top rings where the ring gaps looked like they were aligned with each other. Another thing is my deck height is 1/2 centimeter-like they used the incorrect pistons?? Does anyone know the measurements from the pin to top of pistons on the different Mahle 90.5's? I am going to try and verify deck height once again later and hopefully post some pics-I also need to measure cc's of head. Not sure where to go from here-I know I should but I really don't want to split case-I need to measure side play in rods I guess. Thank you.

[tattooed_pariah]

[Pruneman99]

The difference between A and B pistons is generally 4-5 mm, so yeah, 1/2 cm. I'll second the guess that it got built with B pistons when A were required.

Check out this thread:
https://www.thesamba.com/vw/forum/viewtopic.php?t=612050&start=0

It's about deck heights, but it has the pin heights listed. It's a great piece of work.

[THINGONER]

Thanks for the responses guys-I appreciate it. It looks like from the chart that there is about a 5mm difference in pin height from a to b pistons if I am reading it corectly

[Pruneman99]

[THINGONER]

ok that explains it-you guys have been a huge help I will update when i get the right parts thank you!

[tattooed_pariah]

[THINGONER]

lol yes funny you should mention compression ratio-that is about what I had come up with although just a guess sort of I don't know the cc's of my heads yet. Well in any case I went back out and slid the cylinder over an unringed piston and got a deck height measurement of .104 (thousandths) so I think they did use the A pistons afterall BUT with the top cylinder studs installed the cylinders bind and do not sit flush against the case-I had to remove them in order to a get proper deck height measurement. Also there is a 1/4 "carbon ring at the top of at least some of the cylinders so I do not think the cylinders were seated properly-the studs do not appear to be bent-its as if I need to clearance the stud holes in the cylinder. There were various #s on the pistons-1210 M 0507-top of cylinder and 90P34 underneath where the piston pin goes through cylinder.

[jason]

The carbon will be all the way to the top ring, especially from running bad. You have cylinders oriented correctly, they will hit studs if not? Piston rings turn so being in line means nothing.

[THINGONER]

Ok yes the cylinders are oriented correctly and the top totally bind-maybe they used the wrong diameter studs?? I will check again tomorrow and see If I can make sense of this-I am thinking that the cylinders were seated improperly which led to poor running-not sure tho. Thank you for responding-that makes sense re:carbon ring

[THINGONER]

https://youtu.be/zZmWo5icb_o
Looks like I need to do this-exactly whats happening

[THINGONER]

I gave the engine another look over today and the case studs are 10mm and as I mentioned previously the cylinders are binding and not seating against case-I am thinking to try 10mm to 8 mm step down studs (if they exist) what do you samba people think? My case is a AS41 211 101 102 E. Its in a Thing.

[Rome]

I have a set of used 90.5's in the basement; came off a running engine that has 8mm head studs. Just went down to measure; the cylinder fin stud hole diameters are ~ 11.3mm on the two cylinders of the set. Also have a single 90.5 cylinder which has 11.8mm stud holes. Both sets are old enough to be either Cima, Cofap, or Mahle. Too old to be AA's or other more recent clones.

Even with your 10mm studs, you should have some "wiggle room" with your cylinder stud holes in the fins. Can it be that one or both of the upper studs per cylinder are angled slightly outward so that the cylinder won't clear it? You could probably hold a construction square against the case horizontally and also vertically to check that the studs stick straight out. If the studs were slightly bent, you'd probably have noticed that during their removal to enable getting the cylinders to slip into the case.

How far are you planning to disassemble this engine? Completely? Do you know if your case already has case savers (threaded steel inserts) at each of the cylinder stud holes? If not, you can send the case out to have inserts installed that take the later 8mm head studs.

[THINGONER]

The studs do not appear to be bent-but I have heard of people having to clearance the cylinders even when using 8mm studs-as far as how far I'm going to tear down-it was just going to be a re-ring and valve job, then once I discovered the issue with the studs I thought I could buy step down head studs but I haven't seen any online. It looks like I (or a shop) will have to split the case in order to do it right. There is silicone smeared inside the case at the stud holes-so I think that should be cleaned up and then have 8mm inserts installed-the case does have inserts now. Thank you for replying.

[Rome]

Riverside: Lucky you- looks like you have 2 VW shops right in town- Performance Warehouse, and Car Craft. Replacing the inserts for the 10mm head studs with ones to fit 8mm studs is simple for either one. Just make sure you buy genuine VW 8mm studs, not cheap ones that don't have the right alloy.

You could also consider having your heads machined to use 92mm thick-wall cylinders, to get you 1835cc. There are 92mm TW cylinder sets on which the bottom of the cylinders fit into the same sized holes in the case as your 90.5's, and the thicker diameter at the tops of the cylinders fit into the heads that are bored for TW92 (same diameter as 94mm cylinders).

A thin smear of silicone on the inside of the case over the case saver holes prevents engine oil from seeping through the case and the studs. You could also use Permatex Aviation gasket sealer, but the surrounding area would have to be chemically clean (e.g., brake cleaner spray) for the sealer to stick well.

[THINGONER]

Yep I am pretty fortunate-also real close to Wolfsburg West although they do not service VW-just parts. I think what I am going to do is have the short block tore down and then re assemble pistons and heads myself-I will try and give an update when all that happens-thank you!

[THINGONER]

Some photos from the tear down looks like cam bearing is toast, piston does not look well, crank doesn’t look great either. Is this distance between cam lobe and lifter unusually large?-approximately 3/16 of an inch. Stock cam