New to the site, have an interesting problem!

[66baja68street]

Hello, I am the proud owner of a `66 Baja Bug...

1835cc, dual Delorto carbs, bus trans w/ big nut great reduction.

My baja previously had a 1600 in it until it blew a hole next to the #2 spark plug. Unfortunately the rod bearings were shot (from previous owner). I had an 1835 built with new everything, the weird thing is that with only 12 miles on the new motor it blew another hole in the #2 cylinder head!

Two different motors blow out the same hole in the same cylinder... and it's not the #3! I'm stumped...

[66baja68street]

I'm wondering if it's an air flow problem, I know that there are a million different things it could be... I'm mainly just curious if anyone else has had this problem or something similar.

The engine tins are in place, dog house with wide fan, carbs synced properly, valves are adjusted properly too. I really don't know what would cause the #2 to blow out

[67rustavenger]

Welcome to the samba.
Damn that sux. I have never heard of a hole being blown through a head like that before.
Please post a couple of pics of the hole and your engine in complete form. Some of us here can't read or type But can get to the bottom of the issue with a couple of good pic posts.
Good Luck.
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[66baja68street]

Unfortunately I don't have the heads at this time to take a picture. The first time it blew out in a way that looked like it may have been cracked. The second time, on the new motor, it blew out the spark plug and the surrounding head material. This time it looked melted!

[MrGoodtunes]

[66baja68street]

Thank you! I will check into this as soon as the motor is torn down. Heating issue is my thoughts as well because the fan/shroud and tins were used on both engines.

[mukluk]

I'd be curious to know if the cylinder tin is OEM or aftermarket, and if aftermarket, then is the diverter vane present to properly distribute airflow to the head.

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[Eric&Barb]

Wrong width of cooling fan and/or too small of crankshaft pulley so the fan runs too slow will not help! Check everything, and post images of the engine so we all might spot problems.
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[corvette9]

Are the carbs the same ones? Sounds like that cyl. is running way lean.

[Ravinsomniac]

It's those darned Chinese made muffler bearings..

[66baja68street]

Finally have an update! Motor is back together (New head). Cylinder tins are now complete as they were missing diverter veins. New Bosch 009 distributor installed (shop thought the old one was faulty)...
After a warm up and a quick drive the same culprit cylinder was at 335°f. All other cylinders at 250°f. We found a break in the problem cylinders spark plug wire (New set going on tomorrow morning). The fan is the wide style (in a doghouse shroud) and pushing a lot of air over the cylinders.

I'm leaning towards a lean cylinder, as everything else checks out well.

Any thoughts?

[Eric&Barb]

[KTPhil]

[66baja68street]

I will check into a possible vacuum leak.

Yes the first build on the New motor did utilize the old tins from the original motor. Missing parts should have been discovered by the shop that built the motor, but I'm not one to dwell on the past so it's got complete tins now.

This baja bug has thrown me for a loop! It's been a nightmare but when it's running man is it a blast to drive!

[66baja68street]

The dual delorto carbs that are on this build were on the motor when it blew the #2 head. However the original motor blew the #2 head with a single 34pict carb. Two different engines with two different carb setups wrecked the same cylinder.

I really just want to drive my car! Hahaha

[KTPhil]

Who put the external hardware on the long block, the shop or you?

[66baja68street]

The shop.

[KTPhil]

Just what do you mean by "blew a hole? Post up some pics of the carnage. I'm stumped, too.

Are you running a thermostat? Flaps in the shroud?

[66baja68street]

I don't have the picture anymore but it was a nickel sized hole in the top of the head about 1/2" away from the spark plug hole. The second head that blew (on the New motor) blew out the spark plug and 1/4" of material all the way around it (this time it was obvious that material had gotten very hot).

[66baja68street]

I will have to check on the flaps in the shroud as I honestly don't remember, it's been years since I pulled that shroud out of my 68 street bug. I ran a similar motor for years in that car with that shroud and never had a problem with overheating.