Mcculloch 797, Super 797 thread

[B Royals]

I've finished making blanking plates and rubber gaskets to perform a vacuum/pressure test. When I took the muffler off, I noticed the exhaust gasket wasn't making an even seal and the flange of the muffler had some high spots. I squared it up and it should be good to go.

When I went to put the blanking plate on, I realized the replacement cylinder head needed the recessed square exhaust gasket. I will get one shortly. Out of curiosity though, and being short on time, I wondered if this may give a clue to what cylinder this would be. Short recap, no markings on cylinder, it had the cast un-milled boost port. Does anyone know the history of this cylinder possibly?

Jeff

Edit: In the Aug 69 IPL, there is a note on the exhaust gasket part number, and calls for the square one when using replacement crankcase assy 67420. The thing is though, the regular cylinder number in the IPL is 67420 as well. So I'm not sure of what differences there may be.

 

[jacob j.]

It may a dealer-installed replacement cylinder - most of those had no markings and were not painted.

Sometimes the dealers would stamp it with the part number and the date, or sometimes they would stamp it with an invoice number.

 

[Lee H]

It's difficult to do a pressure vac test on a 797 as the decomp valve has a hole going into the exhaust port which would need to be plugged.

 

[B Royals]

It's difficult to do a pressure vac test on a 797 as the decomp valve has a hole going into the exhaust port which would need to be plugged.

Maybe a silly question here. Shouldn't the decomp valve hold vac/pressure in the cylinder?
Maybe another silly question. Does the top of the tank have to come off to get access to the carb bolts?

 

[Bigmac]

Maybe a silly question here. Shouldn't the decomp valve hold vac/pressure in the cylinder?
Maybe another silly question. Does the top of the tank have to come off to get access to the carb bolts?

In theory, the deco valve should hold pressure, but it is unreliable! I have lapped mine in and the only way I could get it to semi seal with with some grease in there a fairly heavy grease. You can get to the car bolts without taking the top tank off, but it’s not fun, you need to have some pretty thin wrenches to hold the backside of the bolts.