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Hi everyone have a strange problem with my 496 HO..

Having stripped it down to its last nut and bolt and completely rebuilding started and ran fine but only at idle due to not being in the boat, after fitting I took it out for a sea trial and everything seemed to be fine then there was a slight tapping noise and I returned to port..
First thought it was a fuel issue but after further inspection I found that three rockers (two on the right bank and one on the left) had jumped off the push rods, or the nuts worked themselves loose then the rocker was moved.
My questions are my engine is 2001 with very few hours I purchased it from someone who blow up one of his engines and then the boat wasn't used but had some slight moisture issues hence why I rebuilt the engine.
I have to confess I didn't change the valve springs nor the hydraulic lifter as I dismantled them and cleaned them and looked to be fine. The push rods are new and NOT bent so now I'm thinking it may be a oil delivery issue with the lifters or maybe bad valve springs or poor nuts holding the rockers..
On re setting them today I moved the nuts to another place to see if I could see if its the nuts or something else..
Took the boat out and after a short time the noise returned (slight taping) so I went back to port..

Any suggestions would be really appreciated..

Tomorrow I will again take off the rocker covers and find out if the nuts have moved from where I put them or the same cylinder as it was today (with different nuts) has come loose again..

I have tightened the rockers up removing the back lash then a further three quarter turns on each nut to nip them up..
Does anyone know if I'm being correct using these settings??
 

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Hi everyone have a strange problem with my 496 HO..

Having stripped it down to its last nut and bolt and completely rebuilding started and ran fine but only at idle due to not being in the boat, after fitting I took it out for a sea trial and everything seemed to be fine then there was a slight tapping noise and I returned to port..
First thought it was a fuel issue but after further inspection I found that three rockers (two on the right bank and one on the left) had jumped off the push rods, or the nuts worked themselves loose then the rocker was moved.
My questions are my engine is 2001 with very few hours I purchased it from someone who blow up one of his engines and then the boat wasn't used but had some slight moisture issues hence why I rebuilt the engine.
I have to confess I didn't change the valve springs nor the hydraulic lifter as I dismantled them and cleaned them and looked to be fine. The push rods are new and NOT bent so now I'm thinking it may be a oil delivery issue with the lifters or maybe bad valve springs or poor nuts holding the rockers..
On re setting them today I moved the nuts to another place to see if I could see if its the nuts or something else..
Took the boat out and after a short time the noise returned (slight taping) so I went back to port..

Any suggestions would be really appreciated..

Tomorrow I will again take off the rocker covers and find out if the nuts have moved from where I put them or the same cylinder as it was today (with different nuts) has come loose again..

I have tightened the rockers up removing the back lash then a further three quarter turns on each nut to nip them up..
Does anyone know if I'm being correct using these settings??
So you changed to ARP 10mm-7/16 conversion studs and have the rockers set at normal hydraulic setting, right? IF NOT, IF YOU HAVE STOCK ROCKERS/STUDS, they get TORQUED to a specific setting. There is no adjustment. I have a feeling this is your problem. You have stock valvetrain and set them at "normal" BBC hydraulic "zero plus 1/2".
 

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Could be the wrong length push rods, If the cam has been changed.
I agree. I didn't want to go there until I found out which rockers/studs/nuts he has.
 

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Discussion Starter #5
Hi there thank you for getting back to me and sorry for the late reply, ok today went and torqued the rockers at 19 lb ft as stated by the manual (was told by a friend the other method was the correct way... ) Ran the engine and all seemed fine then took it out for a bit to check it under load (2000- 2500 RPM) Then it stopped and I had to be towed back...On returning I checked the compression and I found that the third pot on the right bank had no compression... I then removed the rocker cover and found that the inlet valve had come off the rocker and obviously not opening and then filling up the chamber of fuel. I reattached the valve expecting it to start as normal but nothing.. Checked the fuel and found that I'm not getting anything from the low pressure pump, I did wonder if the filling of the chamber had somehow affected the fuel delivery system and hence no low pressure pump.. Tomorrow I'm going to see if its blocked as am I correct in believing the low pressure filter has a filter screen in it?
 

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Hi there thank you for getting back to me and sorry for the late reply, ok today went and torqued the rockers at 19 lb ft as stated by the manual (was told by a friend the other method was the correct way... ) Ran the engine and all seemed fine then took it out for a bit to check it under load (2000- 2500 RPM) Then it stopped and I had to be towed back...On returning I checked the compression and I found that the third pot on the right bank had no compression... I then removed the rocker cover and found that the inlet valve had come off the rocker and obviously not opening and then filling up the chamber of fuel. I reattached the valve expecting it to start as normal but nothing.. Checked the fuel and found that I'm not getting anything from the low pressure pump, I did wonder if the filling of the chamber had somehow affected the fuel delivery system and hence no low pressure pump.. Tomorrow I'm going to see if its blocked as am I correct in believing the low pressure filter has a filter screen in it?
Yikes.

Yes, there's a screen at the entrance to the fuel pump(s)......not your problem, though.

I think you probably hurt it pretty bad. Start by DISABLING the fuel. Either unplug the high-pressure pump, or otherwise. You can even just unplug the ECM, if you wish. Actually, that would work best.

1) Unplug ECM: this kills ignition AND fuel.
2) Get your valvetrain back in working order.
2) Pull all plugs, push throttle WIDE OPEN, and do a compression test. WATCH valvetrain as you are spinning it.

See that that kicks up.
 

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Discussion Starter #7
Yikes.

Yes, there's a screen at the entrance to the fuel pump(s)......not your problem, though.

I think you probably hurt it pretty bad. Start by DISABLING the fuel. Either unplug the high-pressure pump, or otherwise. You can even just unplug the ECM, if you wish. Actually, that would work best.

1) Unplug ECM: this kills ignition AND fuel.
2) Get your valvetrain back in working order.
2) Pull all plugs, push throttle WIDE OPEN, and do a compression test. WATCH valvetrain as you are spinning it.

See that that kicks up.
Hi I did do a compression test after re attaching the inlet valve and the compression returned to normal, although admittedly not with the throttle open full... Will this morning do it that way. before I did a compression test and was getting anywhere between 140 psi and 170 across the cylinders. The engine had only originally done ten or so hours and was one of a pair that through a rod the boat was later sold and I bought the engine but the engine was sitting around for five years under a tarp hence why I wanted to rebuild it as some moisture had got in over the time and I wanted to make sure that it was all ok. Unfortunately the serial number isn't on it so I can't see exactly what year it is.. Only the number stamped on the block itself is visible..
 

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Hi sh4dive,

x2 on the “I think you probably hurt it pretty bad.” I would highly suggest that you drain the oil and check it for metal shavings. Even cranking the engine to compression test will pump debris through the engine. Do you have a non-bypass oil filter? 140 to 170 PSI is a huge gap between cylinders. I am concerned that you wasted the cam. I wouldn’t want you to do more damage than what has already occurred.
 

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Discussion Starter #9
Hi everyone and thanks for your time and thoughts on this problem, ok today went and checked the screen for the filter and it was blocked I suspect a bit of crud from before had moved from somewhere in the tank (this is the first run on petrol as before this was powered with a diesel engine) have blocked of the return hose and it has good venting in the tank so all is ok there and it fired up first time and ran sweet no miss firing nothing. I am Monday going to change the oil and filter out, I have ordered new nuts for the rockers that came off. These nuts I suspected to be problematic so I moved them to another cylinder to see if the fault moved and it has.. The remaining nuts are still torqued to the correct setting and there has been no movement. I will be checking the oil, this engine has completely been renewed as I explained it had had water get in.. There was slight pitting hence the difference in the compression ratio across the bores. the left bank (where I found some evidence of ingress) they range from 140 to 155 the right hand bank where there was no ingress of any kind the compression ranges from 155 to 170. Since building the engine has run no more than 1 and half hours. I'm expecting until the cylinders bed in some more that they be a little lower although I could be wrong having never really compression tested a newly built engine before. I will wait until Tuesday when I have the new nuts before taking it out to test but will before then be draining oil and changing filter and re doing a compression test then re checking all nuts and torque settings..
 

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OK. Well, as long as you don't have a cylinder (or two) at zero PSI - do the rocker nuts and give her a whirl. I would say - if you have them come loose again, get the ARP conversion studs and some CompCams roller-tip rockers. This will be $200 in parts and a slight upgrade in valvetrain components. This will convert you to standard zero-lash hydraulic setting. That would be your "plan B".
 

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Discussion Starter #11
Ok thank you, makes me feel a whole lot better I can say.. Do you know a site that would sell these parts? Being in Spain makes it difficult to find the right parts..
 

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Ok thank you, makes me feel a whole lot better I can say.. Do you know a site that would sell these parts? Being in Spain makes it difficult to find the right parts..

Chevrolet 496 (8100 series) ARP-135-7201, 10mmx1.5 (base) x 7/16-20 (rocker portion), set of 16. http://www.summitracing.com/parts/arp-135-7201


The Comp rockers are an upgrade in several ways. First, they are a TRUE 1.72 ratio, whereas stock stamped rockers (1.7) are all over the page....1.7, 1.69, 1.68, 1.73.....etc. So, you get a solid 1.72 instead of AVERAGE of 1.7. The roller tip reduces friction at the valve tip(s). They still fit under stock valvecovers.

Comp 1.72 BBC roller-tip rockers: http://www.summitracing.com/parts/cca-1411-16/overview/make/chevrolet

I believe Summit ships internationally.
 

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:) Thank you so much I think I'm going to order them anyway as to improve the valve train I have, can never be a bad thing and for sure it would be an end to the nightmare I have been suffering with these since they was set wrong..
 

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:) Thank you so much I think I'm going to order them anyway as to improve the valve train I have, can never be a bad thing and for sure it would be an end to the nightmare I have been suffering with these since they was set wrong..
Although I have never had a problem with them, I have never really trusted the "torqued" rocker nuts. Just doesn't make sense to me - but it doesn't have to, either. They work in stock configuration, but it's just weird to have NO adjustment to the valvetrain.

I think you'll be much happier with the conversion setup. Especially being "remote" from mainstream engine parts.

PLEASE let us know how it works out.
 

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Discussion Starter #15 (Edited)
I sure will :) I'm going to be ordering them tomorrow so I can take delivery next week.. Just waiting these days for the nuts to arrive is killing me but I still get the feeling I'd be better off with better valve train that is not torqued down. After the problems I'm not sure I'm ever going to feel comfortable with them.. After the few times I've had the failure I'm kinda scared to open it up... An that sure takes the fun out of it.. No good just looking pretty! :)
 

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Today took the boat out for a test run after having spent the day yesterday changing out the nuts, it ran like a champion and just wanted to keep going.. Only took it up to about 3200 rpm was out for about an hour with no issue at all.. The only thing I had is the new secondary in line filter had started to clog up.. Having put more fuel in today I'm guessing it found some more crap somewhere in the tank from it being a diesel.. Will tomorrow change the inline filter and see. Thanks everyone for your input and help.. Can't wait for the upgrades to arrive now! :)
 

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Did your compression numbers even out after it was running smooth? It really sounds like the cam is beginning to eat some lobes. They chuck the pushrods a few times and some adjustments seem to make it right, but you will have issues and high compression on the affected cylinders is one of them. When the lobe wears, it reduces overlap and leads to higher dynamic compression. You said you had the engine apart and checked the lifters, are you certain they went back in their exact locations? A few swapped around on a used cam will destroy the lobes. A cam is a cheap fix compared to running metal through the engine and destroying it. I strongly recommend at least pulling the intake and lifters to inspect the cam lobes.
 
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