1956 Johnson 7.5 HP New Cylinder Head questions

[jeffp102]

Hi,

I've looked through this site and am having some difficulty finding the answers to my questions about my engine, so I decided to lump them into one:

-I bought a new cylinder head for my 1956 7.5HP AD-10, along with the head gasket. Should I use any RTV or any sealant when installing the head gasket ?

-Is it necessary to install new cylinder head bolts ? And, if so, where can I find them ? I've looked all over. I was just planning on cleaning them up a bit, putting some anti-seize on the bolts and re-using them.

-When compression testing the cylinders, what approximately should they be ?

The reason I put a new head on is that the bottom plug stripped out, I tried to put an insert in, and that blew out because I oversized the hole. Looking at the piston chambers, the top one is pretty carboned-up. The bottom is pretty clean. Is that because the headgasket was blown ? Should the top one have that much carbon, or was that because the bottom one was screwed up ?

If you can answer all or any of my questions, Id appreciate it. This engine was my grandfather's and I want to get it running, then restore it as best as I can. I've found some great info on this site about part numbers, paint and decals, thanks a ton.

Jeff

 

[Joe Reeves]

Re: 1956 Johnson 7.5 HP New Cylinder Head questions

1 - I bought a new cylinder head for my 1956 7.5HP AD-10, along with the head gasket. Should I use any RTV or any sealant when installing the head gasket ?

2 - Is it necessary to install new cylinder head bolts ? And, if so, where can I find them ? I've looked all over. I was just planning on cleaning them up a bit, putting some anti-seize on the bolts and re-using them.

3 - When compression testing the cylinders, what approximately should they be ? Jeff

1 - No, if anything, use only oil.
2 - No, there isno need to buy new bolts, Just use grease on the threads.
3 - Compression will vary with the speed in which the engine is cranked over. However, something like 75 psi or so should be okay, best if close to 100.

 

[HighTrim]

Re: 1956 Johnson 7.5 HP New Cylinder Head questions

If the head gasket is the newer shiny material, install dry. I use OMC Gasket Sealing Compound on the bolt threads. I find using oil causes over torquing. The ADs will be around 75 to 95 psi cold and dry.

 

[F_R]

Re: 1956 Johnson 7.5 HP New Cylinder Head questions

I'm with High Trim. I also use the OMC sealant on the gasket unless it is the shiny kind---then nothing. The "shine" is a sealant. Actually, you can install the old kind dry too, but the sealant gives it an extra bit of seal. Use sparingly.

 

[HighTrim]

Re: 1956 Johnson 7.5 HP New Cylinder Head questions

I'm with High Trim. I also use the OMC sealant on the gasket unless it is the shiny kind---then nothing. The "shine" is a sealant. Actually, you can install the old kind dry too, but the sealant gives it an extra bit of seal. Use sparingly.

Best trick I ever got on installing the sealer on the older style gaskets was from you using one of my wifes old magazines with the shiny coated pages. Spreads the sealer perfectly on the gaset everytime. I still have enough pages to do another 50 gaskets.

 

[nwcove]

Re: 1956 Johnson 7.5 HP New Cylinder Head questions

Best trick I ever got on installing the sealer on the older style gaskets was from you using one of my wifes old magazines with the shiny coated pages. Spreads the sealer perfectly on the gaset everytime. I still have enough pages to do another 50 gaskets.

plz do elaborate on the wifes old mag trick.....could take me twenty years .....but i would like to rid the house of those old mags!! lol

 

[HighTrim]

Re: 1956 Johnson 7.5 HP New Cylinder Head questions

The magazine has to have the shiny coated pages. Coat the gasket with sealer, then lay down on a page. Close magazine, then open it. Spreads the sealer perfectly even with a nice thickness. Next gasket use a new page. I used to slop it on, install gasket, then try to clean the sealer off the motor when it oozed out everywhere before reading Franks tip.

 

[nwcove]

Re: 1956 Johnson 7.5 HP New Cylinder Head questions

hmmm, im gunna miss that 1985 edition of canadian living thats been in the bathroom since new....any want a bad recipe for brazed asparagus tips!!!??? lol...before it gets gone!

 

[jeffp102]

Re: 1956 Johnson 7.5 HP New Cylinder Head questions

I Installed the headgasket dry. Cleaned the heck out of the bolts, anti-seize on bolts and plugs. Checked compression...75. Started ran engine, ran fine, I feel like it could perform better,but it is 56 years old. After running it for 15-20 min checked compression again and was still 75 on both cylinders. No leaks. Overall seems good. No looking forward to the re-paint.