What size helicoil do I buy?

[wojciecj]

Recently I purchased a project boat with a 115hp 1973 Johnson on it. As I restored the boat I would periodically start the motor on land. When I went to put it in the water, I couldn't get the engine to run. It would sputter on its own a little then die every time I turned the key. Following that I pulled the spark plugs to check them. When I did this I found out that the threads in the cylinder 3 were stripped. I then decided to do a spark and compression test. The compression test results are as follows: cylinder 1=100psi, 2=90psi and 4=110psi. I couldn't even get the compression tester threaded onto the cylinder head. First, what size helicoil is needed for the hole? The spark plugs that I have are Champion QL77JC4. Secondly, should I be worried about the second cylinder? I know the pressure range should be within 10%.

 

[boobie]

Re: What size helicoil do I buy?

I believe it's 14 mm. Go to a parts house and you'll get the right one. After you get it installed, then check your compression.

 

[Daviet]

Re: What size helicoil do I buy?

I think it's something like 14MM, just tell them you need it for a spark plug, they should give you the correct one. The inserts come in different lenths, measure the thickness of the material where the threads pulled out.

 

[Joe Reeves]

Re: What size helicoil do I buy?

The helicoil is indeed a 14mm one, HOWEVER, check the depth of the threads on your head. Some are 3/8" deep, others are 1/2" deep. If memory serves me right, yours is 1/2".... but check it to be sure so you get the helicoil with the right depth.

 

[F_R]

Re: What size helicoil do I buy?

Better yet, take the head in and have them install the Heli Coil. If they know what they are doing, they will get it straight (very difficult to do free-hand). Shouldn't cost much different than buying the kit to do it yourself.

 

[Joe Reeves]

Re: What size helicoil do I buy?

Yep.... What F_R said.

 

[wojciecj]

Re: What size helicoil do I buy?

Thanks for the advice. I will let you know if I have any more questions

 

[TJS]

Re: What size helicoil do I buy?

Not fond of Heli coils. Time Serts are much much better.

 

[Joe Reeves]

Re: What size helicoil do I buy?

A heli coil allows the spark plug business end to be at the proper depth within the cylinder.

Not familiar with a "Time Sert".

 

[TJS]

Re: What size helicoil do I buy?

Google timesert and you will see what I mean. They are far superior than Heli coil but more expensive and a permanent fix as well. I have fixed a few fords with the kit I have. The also have videos on their site as well.

 

[Joe Reeves]

Re: What size helicoil do I buy?

TJS.... I went the Google route as you suggested, very interesting. I worked with the aluminum blocks, heads etc daily from 1960 to 1991, then occasionally thereafter. Strange that I never came across the Timesert kits. It does appear to be a better fix.