solareclpse2000
Seaman Apprentice
- Joined
- Nov 26, 2011
- Messages
- 35
i did a compression test on my motor and got some nasty results. 1999 merc 200hp 2.5 blue water. carb motor. i was doing a compression test and these are the results. cyl 2- 120 psi 3- 121 4-126 5- 120 6- 119 and number 1 cylinder...... 20 psi. more on that in a bit. besides that for cyl 2-6 are these normal range numbers, or low? i was looking into doing a rebuild in the near future....looks like thats now a priority. but if i had no issue in the 1 cylinder, would these numbers be ok, or would a rebuild be recommended? now, as for cyl 1. i took the head off and found a cip in the edge of the piston, about the size of a BB. on the edge, i can even see the compression ring. the head gasket was broken at the ring seal, where the ring had broken and pushed into the top right cooling port. i flipped the gasket, putting the "bad" part of the gasket on the bottom (cyl 5) and got the same results of 20 psi in cyl 5. 120 in 3 and only 70 in cyl 1. so that tells me the chip in the piston is leaking and a new piston is a must. so i have decided to go with a full rebuild and replace them all. the number 1 cylinder is also marked..... scored, or gouged i dont think is a proper description. its real light. i can see the lines from dragging on the cylinder walls. but they are so light that i cant even feel them with my finger. it looks to me that some how, something small and hard got into the cylinder causing the chip and the breakage in the gasket, but there is no damage, or even a mark on the head. so my main questions here is to determine how i will proceed. full rebuild with pistons is a given, but should i re sleeve? or just get my local machine shop to bore? for correct balance and matching purposes i will do all the cylinders together. instead of say a .010 overbore in just 1 piston. i think a 010 overbore will get the cylinder walls corrected. but is there any performance advantage to doing a 030 overbore? or even 040? is that much save on stock sleeves? how do i determine if i have steel or chrome sleeves? i was also thinking if i got right for a 040 overbore, if i have issues later i have no ability to bore more to repair and such. so i will likley shoot for a 020. just to be on the safe side. unless, the 030 will give me a large power advantage. i know tons of car engines and have been working on cars as long as i can even remember, but out boards are a little different obviously, and this is my first. so any advice is great. what should my piston to cylinder clearance be? and i understand the stock bore is 3.501 inches. so if i go 020 over i will tell my shop to bore the sleeves to 3.521, is that correct? i also understand this is assuming my bores are all still stock. i will look further into that in the next couple days when i have the time and light. and is it really beneficial to shave the heads while is apart? or just a waste of time and money. i want to rebuild it and squeeze out a few extra hp numbers. im planning on velocity stacks, solid engine mounts, exhaust tuner mod, and an above water exhaust outlet from bobs machine shop. thats the plan anyways, with the rebuild being my primary concern and focus. but are these good reliable mods. or just a waste of cash? also, with those mods i would have to rejet and retune my carbs right? i also noticed when i pulled the heads that the guy before me had removed both thermostats. is this ok, or should i get both of them replaced when i build her back up? sorry this is a bunch of stuff thrown out there, but im a little overwhelmed while im trying to plan out this build. thanks in advance.
