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DenLorsTools.com Summary: Since 2005 at DenLorsTools.com and now our most recent tool website, WiseAutoTools.com, we’ve been answering questions on Ford spark plug thread repair kits. It always amazes us that there’s always new questions. A recent inquiry was regarding a 1998 Lincoln Navigator blown spark plug. I recommended the 5553 thread repair kit for the job. The Lincoln Navigator owner would prefer to use the less expensive Calvan 38900 kit and questioned why I made the recommendation that I did. Below is a copy of our correspondence.

The Calvan cannot be used if you have a DOHC. Since you didn’t say what you had; I recommended the 5553 which will work on either. If you have a SOHC engine you can use the Calvan 38900 also. I’ve responded to each of your other concerns below. 

Question - Since this is the first time this hole has had a spark plug blowout, it seems you would want to use the smaller diameter reamer of the 38900 rather than jump to the larger one in the 5553 just in case you have another failure than you could use the larger 5553 for a second chance. 

Answer – That’s not correct. The 38900 kit has larger tooling and inserts. Calvan 38900 insert O.D. is .73″, Time Sert 5553 insert O.D. is  .70″. We haven’t had any repeat blowouts with the 38900 or the 5553.

Question – If you go to the larger reamer in the 5553 and then had a second failure, that would mean no more options except to purchase a new head. 

Answer – That’s not correct. The largest kit is the triple oversize Time Sert 5600 (uses an insert inside another insert). As explained previously the reamer in the 5553 kit is NOT larger than the reamer in the 38900 kit. The largest repair kit is the Time Sert 5600. The O.D. of the largest insert is .76″. If the hole is too large for the 5600 kit, the cylinder head would need to be replaced.

Question – Also, the 5553 does not list a 1998 Lincoln Navigator in its list of cars it will work on (5553 application list).  The chart does list 1999 and newer though. 

Answer – The application chart for the 5553 kit is only a partial list. Since Time Sert kits have stepped tooling to guide the user in straight, they can be used on many engines. The Calvan 38900 kit uses a guide that sits into the spark plug well. That’s why the application of vehicles that it works on is far fewer.

Question – Is there a height difference in the reamers between the two kits making one useable in the furthest back plug holes because it is shorter?

Answer – The Time Sert 5553 thread repair kit’s reamer and wrench assembly is 10.6″ and the Calvan 38900 kit’s Reamer is 7.25″. They both have wrench flats that allow use with an air ratchet. This allows use in a 90 degree angle. This helps tremendously in tight areas compared to drilling with a regular straight drill.

Conclusion – Either the 38900 (applicable engines) or the 5553 can be used on the vehicle, over the fender, in any position spark plug hole on the vehicle. Obviously the further back, the more difficult the access will be. Using either spark plug thread repair kit is a few steps further than gaining access to and changing the spark plugs. Securing heater hoses and wiring out of the way with a bungee cord helps on the passenger side. Sometimes removing the brake power booster on the drivers side is helpful, although not completely necessary. Loosening the fuel rails up on either side is usually needed to allow a straight shot with the tooling.