intake ports on 1996 crossflow

[surrender]

Have a 1985 crossflow block I'am using for a rebuild of a 1996 88 special. Did the 85 have smaller intake ports? On the block I have they are definitely smaller then the 1996 88 block. With the smaller ports should I double check my carbs and make sure I'am not running 1 5/16 carbs(I think they are). I have no history on the 1996 88 I am rebuilding. Are the 1 5/16 carbs right for a 90 hp crossflow rebuild. Thanks in advance.

 

[emdsapmgr]

Re: intake ports on 1996 crossflow

In 1985 there were two different blocks for the V4 crossflow. There was the basic 90 hp block and the high performance 115. Both the same displacement. The 1985 90 should be very similar to your 88, the 115 was the bubble back model and made significantly more torque/hp. It is possible that the 1996-88 is ported differently. Around 1986 OMC changed their hp ratings when they converted from crankshaft ratings to propshaft ratings. Because of that change the same rated engines from 86 and later had to make 10-15% more hp to make up the friction difference in the drive train (lower unit.) A 1996 88/90 hp engine is actually around 100 hp at the crank. To get that extra hp, the porting may be different on the 96 block. I'd be suprised that the 88 engine had 1 5/16" carbs from the factory. The 1 5/16" carbs are considered high performance carbs and are usually found on the older 140 crossflows and all the later 115 bubble back models. It is not a problem to use those larger carbs on the 1985 block, though it is possible that they may overfuel that block slightly-reducing top end potential. You can try them and see how the engine performs. Do you have the original carbs from the 1985 block?

 

[surrender]

Re: intake ports on 1996 crossflow

No original carbs from 85 block,just purchased the block. I'll double check my carbs and go from there. I forgot about the rating change. I also think the 1996 block I have may have been altered by someone because the ports are not very smooth and the intake looks like somebody tried doing some grinding on the interior. I'll try to post pics later. Thanks

 

[emdsapmgr]

Re: intake ports on 1996 crossflow

After reading your comment, I would surmise that the two blocks were probably close to identical when shipped from the factory. On the early 90 engines, the only difference between them and the early (flatback) 115's was the carbs. Go with the 1 5/16" carbs, even though you have low compression heads. I run those same carbs on my 79 85 hp Johnson. Mine does overfuel somewhat at top end-even with high compression heads, but has great grunt out of the hole. Now if only you could find a set of high compression heads.....

 

[toddschubert]

Re: intake ports on 1996 crossflow

Just curios about the rebuild. I own and 88spl that runs fine but has an rpm range that boggs a bit when under heavy load. I'm suspecting carbs but why did you decide to rebuild? what should I be looking out for?
Sorry I cant answe your question

 

[surrender]

Re: intake ports on 1996 crossflow

Engine was runnign great just had a constant problem with lower starboard plug showing whitish deposits on it. Went through ignition, carbs, cooling(think I missed there) and couldnt figure it out. On day after fishing I pulled plugs and decided to open bypass covers and found the lower cylinder on that side had a broken ring. Decided to investigate further and both cylinders on that side had bad rings. After taking heads off found diverters may have been going bad, out of place. I think that side was running hot or just had a carbon build up problem. Had to by new/used block because I damaged the old one removing powerhead.

 

[toddschubert]

Re: intake ports on 1996 crossflow

I had same exact problem w cyl 3 running hot. After replacing entire cooling system I found the water deflectors in water jacket (outside cyl walls @5:30 pos.) to be the problem. Luckily I found it in time doing routine checkup with infrared thermometer. I know I keep repeating the thermometer thing guys but I tell you they are worth every cent diagnosing engine probs.The motor is tough and easy (relatively speaking) to work on. I'll keep an eye on thread and help where I can and learn what I can.
check my post on running hot issue although you are past that point. http://forums.iboats.com/showthread.php?t=524155

 

[boobie]

Re: intake ports on 1996 crossflow

Where did you get the idea to check the water deflectors??

 

[Haffiman]

Re: intake ports on 1996 crossflow

Where did you get the idea to check the water deflectors??

As mentioned, by using an IR temp gun, you will detect hot/cold spots on the engine indicating circulation problems. On engines with deflectors, they are often the cause unless you have an un-even compression/combustion.

 

[emdsapmgr]

Re: intake ports on 1996 crossflow

If you have a deflector problem internal to the block, it is hard to discover. A mispplaced or misshaper deflector hose can cause a hot spot internally which may not show up when using a laser temp gun on the head. Also, you may not get a hot horn, even though the piston may be overheated. Pulling the head is the only way to confirm their positioning and most folks don't do that unless some other problem arises.

 

[surrender]

Re: intake ports on 1996 crossflow

Getting ready to put everything back together. Anyone recommend a good source for pistons and rings? I need both pistons for the starboard side. Looks to be standard size, will be having machine shop verify then after getting pistons they will hone to make sure.

 

[Haffiman]

Re: intake ports on 1996 crossflow

If you have a deflector problem internal to the block, it is hard to discover. A mispplaced or misshaper deflector hose can cause a hot spot internally which may not show up when using a laser temp gun on the head. Also, you may not get a hot horn, even though the piston may be overheated. Pulling the head is the only way to confirm their positioning and most folks don't do that unless some other problem arises.

The head area is not where to 'search' but the bottom of the cylinder cooling channels closest to the crank as well as the top of the block around the regulator area to check for an air-bubble. Pointing at the head, close to the spark, may give you an indication of a 'lean burning' if that particular cylinder is hotter than the others or 'no' burning if colder as it is solid aluminum to the combustion chamber and no water jacket giving a direct heat transfer.

 

[emdsapmgr]

Re: intake ports on 1996 crossflow

Best to have pistons which will expand at the same rate (when they heat up to normal operating temps) as the other two pistons. If the two good ones are factory stock, then get them to match-see your OMC dealer. I would not mix different piston brands in the same block. That also insures they pistons will all weight the same. (same rotating mass.)

 

[wired247]

Re: intake ports on 1996 crossflow

No original carbs from 85 block,just purchased the block. I'll double check my carbs and go from there. I forgot about the rating change. I also think the 1996 block I have may have been altered by someone because the ports are not very smooth and the intake looks like somebody tried doing some grinding on the interior. I'll try to post pics later. Thanks

OMC was all over the place with the 90's and 115's for that matter. Some had 1 inch carbs, some had 1 1/8, some 1 3/16 etc. My 1981 90 HP had the 1 5/16" carbs from the factory with relatively rich jetting which probably explains why its still in one piece. It also has the rubber intake stuffers. It has outrun later 115 bubble backs. If you look at the carb specs for the 1981 engines its a good starting point.