Leak between head and cylinder on reassembled engine

[JSchuster15]

Hello all. I've just reassembled the engine for my CL77. I installed a complete gaskets set during the installation. New head bolt nuts were installed and torqued to 15 ft-lbs. The M6 nuts on the studs between the head and cylinder (by the spark plugs are tight. The knock pins were put in and o-rings for the knock pins. Upon reassembly and start-up, I have an SAE class 4 or 5 leak of oil out of both sides of the seal between the head and cylinders. The leak is coming from the both sides, toward the back of the engine, but not actually the back, still on the sides and then dripping forward off of the front of the engine. If you were looking down on the engine, the leaks would be at about 4 and 7 o'clock. This is my first restoration, but I was meticulous in following the rebuild procedure, referenced hundreds of photos from disassembly, and used all new gaskets/o-rings.

Any ideas on the leak or remedy? The leak is almost "bubbling" out when the engine is running. I'm surprised it is coming from the back portion and not the front. If it were the knock pins and o-rings, I'd suspect it to be at the front.

[JSchuster15]

I should mention that I pulled the tappet covers and the upper portion of the head is getting oil. I thought maybe there was a block and that could be causing it.

[pemdoc65]

I had a similar problem with my CB72 when I rebuilt it. Two of my cylinder studs had backed out part way when I disassembled the engine, and although my torque readings were right, it still leaked. I pulled the engine, tightened down the studs, reassembled, and then all was good. You might also recheck your torque on the head nuts if you haven't already. The gaskets compress after a bit, and you might need to retorque.

[Muddy]

I also had the same issue on reassembly of my CA72. On advice from others, I pulled the engine, stripped off the head, used a new head gasket and o-rings with a coating of gasket sealer. I've had great success with this - no sign of a leak since.

Regards

Muddy

[DJM]

All good points,you also might check that the cylinder studs aren't stretched. If they are the cap nuts will 'bottom out' on the top of the stud without exerting and pressure on the head joint. The studs stretch as they are tightened anyway, easiest check is a trial assembly without the sealing washers then make sure the cap nuts will go down as far as the top cover. If the studs are stretched easiest remedy is to remove the stud and cut a few extra threads on the bottom end and shorten to suit.

Although only the front outer studs have dowels and O rings fitted there is also oil present in the rear outer studs / holes so a smear of gasket sealant around the rear studs is a good precaution too.

Good Luck,

[Tim Allman]

I had a similar problem after a rebuild. It turned out that the cylinder sleeves were just a bit too proud.

[AlanW]

All of the above need checking also check the liners are not below the surface of the barrel/jug.
Al.