Why is my engine so hard to start?

QUESTION: I have a 1979 Cessna 152 II with a Lycoming 110 hp engine. I have a hard time starting it in all weather conditions with any combination of prime, from zero to four primes. Many times it will not start, draining the battery. How can I resolve this problem?

Joe Ragon
Okeechobee, Fla.

ANSWER: I could have used more detailed information regarding your engine, such as the serial number, total time, etc., but let’s see if I can at least give you some ideas for some simple troubleshooting. First, because of the age of the aircraft and assuming it has its original engine, the first thing I’d check are the magnetos. I’d suggest you have your maintenance facility review Lycoming Service Letter L 210, which is a reprint of a Slick Bulletin. If this has already been accomplished, let’s move on to a few other things that may be contributing to the problem. While we’re talking about magnetos, make certain the mag to engine timing is set correctly. The proper timing is stamped on the engine data plate and also printed in the Lycoming Operators Manual. Unfortunately, Cessna chose not to provide a Lycoming manual with its aircraft, so hopefully it covered important information such as this in the POH. I also recommend that you check Lycoming Service Instruction SI1374B, which covers upgrading the Slick magnetos to a more improved model. This is known to help with hard starting.

Not knowing what kind of maintenance history you’ve had, I’d check to see if the spark plugs are in good condition and are set to the proper gap. We always want to be sure we’ve got the three basic things required to make an engine run — fuel, fire and air — before going crazy or spending lots of money. Since the spark plugs are our source for fire, we want to know they’re in good working order, properly gapped, and not lead fouled. We also need to see that we’re getting the fuel when and where we need it. I’d suggest you review the starting procedures in your POH just to be certain you’re not overlooking something that could help us here. With regard to air, there would have to be major problems in the induction system that would cause us not to get enough air to at least get the engine started.

One other thing: Cessna choose to install a 24-volt starter on this aircraft. In addition to the magneto modifications and changes mentioned earlier, there was a starter replacement covered in Lycoming Service Instruction SI1383. This replaced the original starter with a slower turning starter which, as I recall, also helped with the hard starting situation.

I suggest that you research the entire maintenance history of your aircraft before doing anything else and check for compliance with the publications I’ve mentioned and any others that may be related to your problem. By doing this you may go right to the problem area without spending lots of money trying different things that may or may not work.

QUESTION: We are working on a Lycoming IO-360b1b. The rockers are stamped 69443d. This part will not show up on our parts list. Is it the intake or the exhaust? I believe the rocker with the oil squirt hole pointed to the spring is the rotater. HELP!

Mike Habermehl
Mt. Sterling, Ky.

ANSWER: The question you asked is simple to answer, but could be somewhat difficult for a lay person to put his finger on, so I’m glad you asked. The part number that you found stamped on your rocker arm is a subassembly part number. In this particular case, when this part is completed, it becomes a part of finished part number 69444. The 69444 rocker arm was used as an intake rocker arm on several different models, along with the part number 74636 rocker arm, which was used as the exhaust valve rocker arm on these applications. Note: These were not interchangeable with one another.

I’d also recommend that you or your maintenance facility take a look at Lycoming Service Instruction No. 1454 dated June 5, 1991, for clarification on this issue.

Paul McBride, recognized worldwide as an expert on engines, retired after almost 40 years with Lycoming. Send your questions to: AskPaul@GeneralAviationNews.com.


  1. Bill Bresnan says

    Hello Paul. I have a Lycoming IO-320B1A which I’m converting to fixed pitch. (making it a B2A). It has the WCF. I see that the original engine called for (2) impulse mags (S4LN-21) 10-51360-30. I was able get a good deal on two newly rebuilt mags, but only one is an impulse. It is a S4LN-21 (10-51360-37) and the other is an S4LN-20 (10-51360-29). Can I use them on my engine which is installed on my homebuilt biplane? Thanks for any help or guidance you can give me. I know if I’m able to use them I will have to remove the spacer on the right mag.


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