260hp I/o expectations

[1224bret]

Well from the few that have this set up sounds like I'm pretty close to where I should be. I think the engine that was swapped in was quite possibly a automotive engine. The reason I'm thinking of chain stretch is that I can't seem to get the timing right. It won't run right without the timing light showing around 29* advance at idle I still have to check and make sure the pointer and balancer match up at top dead center, probably my first weekend project. I tried to set it at 8* but it doesn't want to start with tht timing and at 8* initial I can only get 27mph top speed and forever to get on plane. I don't seem to have any detonation where it is now and I think I'm actually still somewhat retarded as far as what it sounds like now. I will do some more checking and try to get some fresh fuel in it this weekend. I just rebuilt the carb but I need a new secondary metering rod hanger since mine looks slightly bent. This thing has been a can of worms since I got it. Thanks for all the help and if anyone has more performance numbers with this set up I'd appreciate it seems like not many 260hp I/o's are out there. Thanks agian!

[step up here]

Look for the serial number on the block Mecruiser has them on the right rear side of block. Providing its a merc.

[1224bret]

Wdlyle I agree it gets there pretty quick acceleration is great I guess I just expected more top speed. I don't run wide open very often but it's fun to get on it now and then. Pushing 40 isn't bad but 10mph faster would be nice. Either way I'm really happy with my v20!

[wdlyle]

I agree, I expected a little more out of my 260 when I bought it seeing what others are getting with lower HP engines.

[smokeonthewater]

weirdness with timing is more likely to be in the harmonic balancer than the timing chain... tho 29* is a LOT... you ARE checking timing on the correct cylinder arent you?.... had a buddy who always had fords try to check timing on the right front of a chevy once and it didn't work for him LOL


If you pull out #1 spark plug and use a screw driver to feel the top of the piston you can determine if it is at TDC and then mark the balancer in line with the tdc mark....
You can check for slop in the timing chain by turning the crank back and forth by hand with the dist cap off so you can watch the rotor.... there WILL be a little slack but shouldn't be a lot.

I haven't had a 260 in a V20 but I did have a '78 merc 898 (198 hp 305) in an arrowglass siesta... 20' deep V cuddy... It ran 40-42 mph with a 14"x19" old school 3 blade stainless prop.

[step up here]

Pretty tough to beat a 200hp or more outboard. Especially a new four stroke,you need a worked 350 with around 500hp see back post under Ubhistory He built one put in a V-20 went around sixty mph I believe.

[1224bret]

Yeah the timing has me baffled. My bet would be I'm giving up a few ponies just by the timing being off. I have some timing tape and have thought about making sure it was at tdc compression and making my own mark to go by. I don't know how the balancer would be that far off either though.... I've tried two timing lights and got the same result. I may have a little time tomorrow to look at it. I'm sure I'm looking at the right plug wire it's the front left wire if your standing behind the engine correct? Would a better prop turned at the same rpm give different results? I have quite a bit of checking on stuff left but I think I'm on the down hill ride now. I know the outboards have a better power to weight ratio but I would have thought the 260 would have cranked out a little more...

[smokeonthewater]

yep left (port) front if it's a chevy

4200 is a bit low too but could all be in the motor..... 4400 would be better

Get that fresh gas in first and then get the timing right


The balancer can be off just from being old and moving on the rubber... It can be off from not having a key in it... It can be off because the timing indicator on the timing chain cover can be in the wrong place IE mismatched parts.

[reelapeelin]

Originally Posted by 1224bret

Well from the few that have this set up sounds like I'm pretty close to where I should be. I think the engine that was swapped in was quite possibly a automotive engine. The reason I'm thinking of chain stretch is that I can't seem to get the timing right. It won't run right without the timing light showing around 29* advance at idle I still have to check and make sure the pointer and balancer match up at top dead center, probably my first weekend project. I tried to set it at 8* but it doesn't want to start with tht timing and at 8* initial I can only get 27mph top speed and forever to get on plane. I don't seem to have any detonation where it is now and I think I'm actually still somewhat retarded as far as what it sounds like now. I will do some more checking and try to get some fresh fuel in it this weekend. I just rebuilt the carb but I need a new secondary metering rod hanger since mine looks slightly bent. This thing has been a can of worms since I got it. Thanks for all the help and if anyone has more performance numbers with this set up I'd appreciate it seems like not many 260hp I/o's are out there. Thanks agian!

Spare...do they make the electronic (Petronix?) ignition for this motor...that might help him out some here...

[step up here]

It should the thunderbolt IV system which is very good!