Poor Compression

mikeporterinmd · Posted: Thu Sep 21, 2006 3:24 pm Post subject: Poor Compression

We're looking at a 1999 TomCat with only 110 hours on the meters. However, a
compression check shows a range of 110-140, with either two or three
cylinders on each motor reading low (below 10% of the top). There are two
cylinders in the 140-145, range.

I'm not sure if I should post the exact readings since the test was done by
the broker and I did not pay to hae it done.

Anyhow, we're trying to figure out what a fair offer might be. I'm guessing the
motors were not properly winterized and rusted, and therefore entire powerhead
is shot (100 4s yamahas). How about the lower end? I don't know how
to test it short of disassembly.

It's a shame since otherwise the boat appears to be nice. Also, complicating the issue is that the boat is 1500 miles from me.

From what I'm told, the motors do seem to run OK, but I would guess that this will not be for long. But, it's not like older TomCats are common and a proper offer followed by repowering done at a local shop so the results can be serviced might not be a bad idea.

Any thoughts?

Papillon · Posted: Thu Sep 21, 2006 3:35 pm Post subject:

I would not be overly concerned by the 110 or the 140 readings at to the top range, but the fact that there is such a big difference between the two numbers is of great concern. Do you have someone knowledgable in the same area as the boat is located, that my be able to check it out up close and personal for you? Ask here and one of the C-Brats may know the history on the boat and help you out.

Good Luck

Sawdust · Posted: Thu Sep 21, 2006 3:51 pm Post subject:

Way too much difference - I would have a well-qualified technician perform a leak-down test on both engines.

Do you have valid history on the engines? Long periods of inactivity without proper preservation? Many questions. A survey by a good technican is certainly in order. I've bought with a "purchase subject to engine and hull survey" and not been sorry.

My 24 Tomcat was a great boat and worth the effort IMO to see if you can make it work. I presently run a 100 Yamaha on my 22 C-Dory and am not aware of any engine weaknesses.
Joe will know.

Dusty

Sea Wolf · Posted: Thu Sep 21, 2006 4:30 pm Post subject:

I've not run into any repetitive or problematic weaknesses with the 1.6L Yamaha block that is used on the 75,90, and 100 hp models, and I've searched numerous engine sites for them.

There are some problems with the 115, in which the block has been upped to 1.75L and beefed up parts installed in the short block, but most of them are due to the harder nature of the metals in those different parts and a lack of sufficiently hard run in time to seat rings, etc. Results in blow by, gas in oil ("making oil"), compression losses, etc.

One possible reason for differential compression pressures might be carbon deposits siezing up of the rings from excessive low rpm (trolling) operation, which might be cleared up with carbon removal additives and treatment (Seafoam), which could free the rings and allow them to run in again and seat. Might look for excessive carbon deposits through the spark plug holes and look for the same in the exhaust manifold covers, if available for inspection. (W/O looking, not sure if the dual overhead cam design allows for this feature and inspection.)

Is there a top to bottom pattern in the compression differences that would indicate different operating temperatures vertically in the engine block due to cooling circulation?

Larry H and Steve are ex-OB mechanics and can add a lot to this discussion.

Joe.

Larry H · Posted: Thu Sep 21, 2006 5:42 pm Post subject:

Mike,

I would go with Dusty's idea of a cylinder leakdown test done by a qualified mechanic. This will let you know more than a simple compression test.

I would treat the motors with a de-carbonizer chemical (one brand is Engine Tuner by BRP[Evinrude]) and rerun the compression test and the leakdown test. The de-carbonizer chemical will free up the rings if they are stuck.

The lower unit can be checked for leakage (without a teardown) by removing the drain plug and checking the condition of the gear oil for water or metal filings. If you only remove the drain plug and not the vent (upper) plug, a small amount of oil will run or drip out and can be caught in a glass jar for inspection.

Sawdust · Posted: Thu Sep 21, 2006 5:52 pm Post subject:

Sure glad you are here, Larry!

I know what to ask for - you know how to do it. The old 24 TC with a pair of good Yamahas should be a winner. Wish I had mine back, but water over the dam, eh?

Duster

BrentB · Posted: Thu Sep 21, 2006 8:02 pm Post subject:

If this boat is the one in SW FLorida, I looked at it in August and thought it was in excellent shape but suffered from TB,,,,, tired bottom from sitting out of water for far too long. It was being sold for consignment and they dropped price but had no trailer. As I understand the situation, the boat is from South Carolina and the owner recieved the boat from an estate and the owner has posted couple of CB messages. The boat was shipped FL b/c the owner thought it would sell faster at a CD yard. The hull was ding free and no dock marks. It does not have trim tabs and the electronics could be update just like computers..... new models every 6 months. I was busy working on my father in law's home and got the electrical panel replaced and one bathroom updated. One afternoon I left for Home Depot to pickup a new sink and faucet usually an one hour trip and drove to the boat yard. They had one of each C-Dory models in stock including a new TomCat and C Ranger 21EC. Since this was the first experience looking and getting inside each boat except the new TC, I ran out of time and they wanted to go home. I spent about 10min looking at 99 TC and didnt see any problems. Engine covers were abit faded but so what. The inside was so roomy and so was the cockpit. I am 6'4' now, days ago 6'5" and saw the berth and said "Wow", plenty room for 2. Adm My Better Half is 5'"11 1/2" and I got the smile instead on the Dead Fish Voice. We drove back the next the day for a hour but returned for more home repairs. I have never see so much damage in person caused by a Hurricane in this case Hurriance Charley and am and stilll so overwhelmed and proud how the community assisted each other, adapted and over came hardships. So many lost everything and so many started over. So sorry off on a tangent, the engines look fine to me but they were not running but didnt see any leaks and prop or lower unit damage. My impression was this was a dream boat and a deal if I more time to jump through the hoops for a test drive. More time..... One kid in college, one in middle school and I work 2 jobs. I have an old non running Renken in FL and was looking the web for parts, advice,...yada yada, and decided to start looking at new boats on iboats and saw a TomCat which lead me to CB site. My first posting. Being looked at as a spammer then vetted into the CD world. Wow! so many stories, trips, experiences, jokes, colorful characters, experts, ...... I thought rhe TC in VT was a complete package. I plan to look at the FL TC at the end of October if has not been sold. I also loved the CRanger except for the tiny cabin but loved the cockpit and the canopy. Good lucK and I hope you buy it b/c the only cure for TB is a good fishing trip and cruise and I always wanted to go tarpon fishing by Boca Grande and now cant wait to go to PNW, salmon fishing, do so crusing, visit the C Dory factory and go a gathering which I assume is code for party.

Sorry for the long story. I should be working on my presentation but always time to check the CB site.

mikeporterinmd · Posted: Thu Sep 21, 2006 9:43 pm Post subject:

mikeporterinmd · Posted: Thu Sep 21, 2006 9:53 pm Post subject:

mikeporterinmd · Posted: Thu Sep 21, 2006 10:05 pm Post subject:

Sawdust · Posted: Thu Sep 21, 2006 10:27 pm Post subject:

Something doesn't smell right to me... my suggestion would be to hire a good, qualified mechanic and get a real survey. There is way too much variance in first and second tests... and without knowing exactly how the tests were done you doin't have anything worth hanging your hat on.

Larry?? Your take? I've been a victim of too many half-arsed tests by.. (you name them). What the tester did and how he did it is very important. If the price is right on the packagie, not to worry.

Dusty

mikeporterinmd · Posted: Fri Sep 22, 2006 11:00 am Post subject:

Larry H · Posted: Fri Sep 22, 2006 1:07 pm Post subject:

Here are a couple of ideas.

Contact a Yamaha dealer and find out how much it would cost to replace the powerheads. Keep this figure in mind when you negotiate the price.

Test drive the boat. Run the motors at wide open throttle and see if the rpm's are in the full throttle range. After the test run, ask for a compression test to verify the earlier results.

If these motors only have 110 hrs, they are barely broken in.

Buy an aftermarket extended warranty to cover the motors.

Sea Wolf · Posted: Fri Sep 22, 2006 1:10 pm Post subject:

Larry-

Damn smart ideas! Idea

Joe.

gljjr · Posted: Fri Sep 22, 2006 6:20 pm Post subject:

My guess looking at the compression numbers is that the Starboard engine has a blown head gasket between 1 and 2. My guess is that the port engine is fine (looking at these numbers (110-120-125-130) but I'm very concerned about the numbers from the startboard engine.

My guess is that the test with higher numbers is invalid. I've never yet seen a non diesel engine with a compression of 160! Something is fishy there.

Do yourself a favor and get a good surveyor to check this boat out and make arrangements to have a respected mechanic check out the motors as everyone above stated. Then figure out what you are willing to pay for the boat figuring in new motors into the price realizing that you would likely replace them in X years. That is what I did with my 27 and I don't regret it even though it is taking me way to long to get the motor installed.