On a November morning back in 2013, I got a call from RD in regards to a project boat that needed some attention. RD wanted to have the jet rebuilt and some cosmetic upgrades done to the boat. Details were kept to minimum, but I did gather that the boat belonged to an RDP board member and expectations were high. The subject is a 1976 Spectra 20. The boat arrived, it seemed well kept. The initial plan was to run the boat before the jet rebuild, document the RPM's and speed, and repeat the process after the jet upgrades were done. The Spectra was powered by a mystery 454 and a seemingly worn out Dominator Jet. The pump was equipped with a Place Diverter. The 454 had no available history other than a thought that it was recently rebuilt before.
I was asked by Forensic (boat owner) to check the timing before we did our lake test. The boat had 34 degrees of total timing, a normal number so it was off to the lake. The boat was a little sluggish to roll over, nothing unexpected for a heavy jet boat. The mid range acceleration seemed ok, nothing exciting, but enough to get you down river. On the top end, the boat was considered normal for its size and weight. Not knowing anything about the engine, it was hard to speculate where it should run. I did report that the last quarter throttle was unresponsive giving the boat a stuck feeling on the top end. The boat was making its way across the lake at 54.7 MPH (GPS) while the motor was turning 4400 RPM's. This is a pretty normal scenario for a boat like this. Yet, I was still unsettled about the throttle gap on the top end. After getting off the lake, I put in a call to RD to express my concerns and the need to run a leak down test on the engine.
Once back at the shop, I started the leak down test. For those not familiar with a leak down test, not like a compression check, a leak down check is performed by putting 100 psi of air into the cylinder with the piston on TDC (compression stroke). If the cylinder leaks air pressure, you can feel where the air is leaking. If you have air coming back up thru the carb, you have an intake valve leak. If you have air leaking thru the exhaust, you have an exhaust valve leak. If you have air leaking thru your valve cover breather, you have air passing by the piston rings. A normal leak down result would be 5-10 percent. So if we put 100 psi into a cylinder, and the cylinder is holding 90 psi, that cyIinder is considered normal (as long as the leakage is thru the crankcase). If at any time you have air leaking by the intake or exhaust valve that is cause for concern. Valves can sometimes have a slow process of deforming which can cause them to eventually break and cause major engine problems. Catching a valve going bad or a valve seat problem in advance would be a lucky day for you.
The results of a leak down check can vary for many reasons. A cold engine versus a warm engine will yield different results. Rust contaminants on a valve seat can show an air leak where a part is not necessarily broken or going bad. Leak down results can also vary on supercharged engines. Traditionally, you can expect more crankcase blow by from a supercharged engine (especially cold) compared to an aspirated engine. Naturally, an older engine will show higher crankcase leakage due to engine wear. If you have a cylinder leaking down at 14 percent crankcase, there is no cause for concern. Just use common sense when looking at leak down test results.
As I pulled the number one spark plug I noticed it was loose. Seemed odd, but I continued on with the test. As I progressed down the line the loose spark plug problem was not isolated. Cylinders one and three seemed to be holding good pressure, but number five was leaking 23 percent (crankcase). Number seven was good. Going to the other bank I found the number 2 hole to be completely dead. 100 percent leakage (exhaust valve). I also noticed that the electrode on number two was burned away. Number four was ok, number six was leaking 38 percent (crankcase) and number eight was ok. All of the spark plugs were loose. I had a pretty good picture painted by now. When a motor is detonating it can rattle the spark plugs loose. After seeing the plug burned away on number two, every spark plug rattled out of the motor, and knowing we had a bad exhaust valve, it was pretty evident at that point that this motor had or has a severe lean condition.
Upon pulling the heads off, I found this gem on the number two hole. This valve is cracked roughly 320 degrees around. I figured if I would have made one more pass at the lake this motor would have eaten itself alive. Broken off valve heads are a major disaster, quite commonly breaking pistons, heads, and engine blocks. This was a close call.
With the heads off, it became pretty obvious what we had going on. The motor had high profile pistons installed. With 119CC heads, I estimated the compression at 10-10.5- 1. An iron headed motor on pump gas in a heavy load application. It didn't stand a chance. To boot, it had stock GM valves that will not take that type of abuse. I was not impressed with the ridiculous usage of silicone during the engine assembly.
My suggestion was to tear the motor down. The cylinders showed excessive crankcase leakage on two holes so it just didn't make sense to try to patch this engine up. With approval, I tore the motor down. The bearings were already pretty scored up, a clear sign that the engine was put together dirty. The amount of blue RTV silicone used during assembly was not good. The oil pan was full of broken off silicone fragments. I also noticed that the engine had the wrong head gaskets installed. Overall I was not impressed with the engine assembly or cleanliness.
I finished tearing the engine apart, removed all the plugs, cleaned parts up a bit and headed over to Clay Smith Cams. I have used Clay Smith Cams for all of my machine work for years. I have dabbled with other machine shops only to be disappointed and frustrated when stuff is not machine properly. Old George at Clay Smith has a depth of knowledge second to very few and he is always very friendly to work with. I cant say enough about the crew over at Clay Smith. I sat down with George and we assembled our new engine on paper. With the engine machining underway, I was headed back to the shop to tear into that Dominator jet.
Look for article two as we continue on the Spectra journey.
Bob Jeanblanc
Marine Industries West
BJ's Marine
714-630- 3905
