900sc - broken valve spring
09-12-2002, 03:58 PM
#21
Registered
Join Date: Mar 2001
Location: st. clair shores mi ,us
Posts: 1,620
Likes: 0
Received 0 Likes
on
0 Posts
Tinkerboater, JimV,
Check out www.lsmeng.com
He is one of the places I talked to about hydralic roller cams.
Check out www.lsmeng.com
He is one of the places I talked to about hydralic roller cams.
09-13-2002, 06:46 PM
#22
Guest
Posts: n/a
Rebuild valve train after 50 hours
KWB
Check out your Merc owners manual, they say that you should rebuild the complete valvetrain every fifty hours! People may have good or bad opinions about Merc High Performance but one thing that I have learned from dealing with them is that they do a lot of endurance testing on their engines (much more than any local engine builder can afford to do!). You may get a lot of different opinions about what to do but I would think long and hard before changing the set up. This is hard for me to say because I tinker with everything! Please read the owners manual over and over again until you have it memorized, it really helps!
Sincerely
Dennis Moore
Mercruiser Master Tech
writer for
FAMILY AND PERFORMANCE BOATING MAGAZINE
author of HP Books
BIG BLOCK CHEVY MARINE PERFORMANCE
SMALL BLOCK CHEVY MARINE PERFORMANCE
Check out your Merc owners manual, they say that you should rebuild the complete valvetrain every fifty hours! People may have good or bad opinions about Merc High Performance but one thing that I have learned from dealing with them is that they do a lot of endurance testing on their engines (much more than any local engine builder can afford to do!). You may get a lot of different opinions about what to do but I would think long and hard before changing the set up. This is hard for me to say because I tinker with everything! Please read the owners manual over and over again until you have it memorized, it really helps!
Sincerely
Dennis Moore
Mercruiser Master Tech
writer for
FAMILY AND PERFORMANCE BOATING MAGAZINE
author of HP Books
BIG BLOCK CHEVY MARINE PERFORMANCE
SMALL BLOCK CHEVY MARINE PERFORMANCE
09-13-2002, 09:26 PM
#23
Registered
Dennis, what does a complete valvetrain rebuild mean? New springs and lifters or does the heads need to come off to do valve seat / guide work? Just curious, I run a solid roller in my motor also with slightly more duration and lift than the 900SC cam and feel 50 hrs for springs and lifters is about right for me also. Hopefully nothing else though!!
09-15-2002, 04:03 PM
#24
Guest
Posts: n/a
Valve rebuild
I never got around to asking what the Mercruiser High Performance Division had in mind when they suggested a complete valvetrain rebuild after 50 hours! Even when I worked for Hallett Boats (almost 9 years) we didn't see many 900 SC engines. On the few 900 SC engines that we serviced I suggested that we rebuild the valvetrains on the engines and everyone looked at me like I was nuts! (what did I know, I was only the mechanic!) Even very knowledgable boaters can't believe that this type of service work is required after only 50 hours of running time. If it ever would have come down to rebuilding the 900 SC valvetrain I would have inspected everything and only replaced parts that looked worn out (or ground the valves if they needed it).
I would say that to make 900 horsepower that the camshaft has some really fast opening and closing flanks that require high spring pressures to keep the lifter following the lobe. The stiff springs puts extreme pressure on the lifters/lobes at idle (when the engine is running at high speeds the upward inertia of the lifter counteracts the downward pressure of the spring relieving some pressure on the lifter roller but at low speeds you have less upward inertia of the lifter, this creates excessive downward pressure on the lifter/lobe from the stiff valve springs). This would make camshaft and lifter INSPECTION (not necessarily replacement) very critical. You should find out as much as you can about these parts and learn the signs of failure.
Closing the valves very quickly with a combination of steep closing flanks on the lobes and stiff valve springs would be very hard on the valve seats. Owning a 900 SC for any length of time would mean investing in a good valve spring compressor, periodically remove the heads and inspecting the valves and seats for damage (learn as much as you can about valves and seats). It might be economical in the long run if you also invested in a valve spring tester. These two tools could save you some money by fortelling future engine failures (knowing when to replace the parts) and give you confidence and peace of mind in your engine while you are out boating.
No one (but the boat salesman) said that owning a 900 SC would be easy.
Sincerely
Dennis Moore
Mercruiser Master Tech
I would say that to make 900 horsepower that the camshaft has some really fast opening and closing flanks that require high spring pressures to keep the lifter following the lobe. The stiff springs puts extreme pressure on the lifters/lobes at idle (when the engine is running at high speeds the upward inertia of the lifter counteracts the downward pressure of the spring relieving some pressure on the lifter roller but at low speeds you have less upward inertia of the lifter, this creates excessive downward pressure on the lifter/lobe from the stiff valve springs). This would make camshaft and lifter INSPECTION (not necessarily replacement) very critical. You should find out as much as you can about these parts and learn the signs of failure.
Closing the valves very quickly with a combination of steep closing flanks on the lobes and stiff valve springs would be very hard on the valve seats. Owning a 900 SC for any length of time would mean investing in a good valve spring compressor, periodically remove the heads and inspecting the valves and seats for damage (learn as much as you can about valves and seats). It might be economical in the long run if you also invested in a valve spring tester. These two tools could save you some money by fortelling future engine failures (knowing when to replace the parts) and give you confidence and peace of mind in your engine while you are out boating.
No one (but the boat salesman) said that owning a 900 SC would be easy.
Sincerely
Dennis Moore
Mercruiser Master Tech
10-30-2016, 01:03 PM
#25
Platinum Member
With a 900 sc, can you really keep the rpm in check with the blower spooled up and running hard?
I run a Big Chief head with long valves which can be a little hard on valve train.. I started out using a s/r with crowers's cutaway severe duty lifter and tool room springs at 250#. Cam was .714" Average life was about 50 hours at a cruise of 3500 rpm. Did this twice. Went to a crane h/r with .632" lift and 150# springs. Made about the same hp at 5500 as s/r cam, lost about 100 hp due to lower rpm. After 105 hours, almost all cruising I had one rough lifter in each motor. Went back to s/r, cut the cam back about .030 in lift, added a KE lifter spray bar in intake valley, used crowers same lifter but with the extra oiling hole to lube bearing axle and lowered springs to 210#. So far, I have 115 hours, check lash every 5 hours just to make sure nothing changes. So far so good. My thought is that if it works with this config should be even better with a lighter valve train??
I run a Big Chief head with long valves which can be a little hard on valve train.. I started out using a s/r with crowers's cutaway severe duty lifter and tool room springs at 250#. Cam was .714" Average life was about 50 hours at a cruise of 3500 rpm. Did this twice. Went to a crane h/r with .632" lift and 150# springs. Made about the same hp at 5500 as s/r cam, lost about 100 hp due to lower rpm. After 105 hours, almost all cruising I had one rough lifter in each motor. Went back to s/r, cut the cam back about .030 in lift, added a KE lifter spray bar in intake valley, used crowers same lifter but with the extra oiling hole to lube bearing axle and lowered springs to 210#. So far, I have 115 hours, check lash every 5 hours just to make sure nothing changes. So far so good. My thought is that if it works with this config should be even better with a lighter valve train??
12-24-2016, 10:42 AM
#27
Charter Member #40
Charter Member
Initially we had DelWest titantium on both. Then stuck an exhaust in the guide and DelWest suggested getting the titantium out of the exhaust side with the low cr of 10:1. Eventually got rid of the Big Chiefs and went to a Canfield head. Realizing you can't compare heads. Also went to 8-71's and intercoolers which helped make up the dif. But life was good with KE's spraybars and Crowers SD solid rollers in the revised config. Still replaced rollers every 125 to 250 hrs. Used the Isky 8200+ spring and replaced every 250 hours. Jessel went thru rockers every 250 hours. Never a failure.
