980 hours on engines - compression test

[tpenfield]

Yes, I think the cam he used had 44 degrees of valve overlap. Kind of on the hairy edge for a marine engine; fine for an automotive engine.

I wonder if the engine eventually hydro-locked?

 

[Scott Danforth]

- if you give an engine the cam to enable reversion, it will, regardless of what the static level is.

heck, I was able to see reversion at idle with the motor on a pallet.

 

[tpenfield]

heck, I was able to see reversion at idle with the motor on a pallet.

So, we are thinking RSBJ hydro-locked the engine and chose not to talk about it :noidea:

 

[Scott Danforth]

dont know. from what I found, simply adjusting base timing will affect vacuum at idle which will affect reversion.

my guess, is he was on the raged edge of reversion and probably had wet valves every time he keyed off. motor could live in that scenario for a while. however one rapid key off and it could have hydrolocked.

 

[tpenfield]

dont know. from what I found, simply adjusting base timing will affect vacuum at idle which will affect reversion.

my guess, is he was on the raged edge of reversion and probably had wet valves every time he keyed off. motor could live in that scenario for a while. however one rapid key off and it could have hydrolocked.

Probably so. . .

It seems as though you can get a cam with almost no overlap, or the next step up is about 45 degrees of overlap, which is on the outer edge for marine use. I haven’t seen anything with about 20 degrees of overlap, which may be a whole lot safer for marine use, yet offer a bit more performance.

I would think that Mercruiser does not want to run any sort of risk of reversion and goes with the mildest cam.

 

[Rick Stephens]

For some reason 12º max overlap sticks in my head as Merc's recommendation.

 

[tpenfield]

Good discussion on cams and valve timing . . . I am thinking to stay with OEM on the cam.

I do have a question about the upper end of connecting rods . . .

I see that some engine have a bushing/bearing for the wrist pin, while others do not. Here is the diagram for my engines . . . it looks like there is no bushing at the wrist pin end of the connecting rod, or at least it is not ID;d as a serviceable part.



Do some engines not have a bushing there? I would assume this would wear, so is the remedy to replace the connecting rods if there is excessive wear? (i.e. out of spec)

TIA for any info on the wrist pin/connecting rod bearing/wear.

 

[alldodge]

You have pressed fit pins, so the pins float on the connecting rod and do not move on the piston ends. They require a press to install and remove

Full floating pins use snap rings on each end of the pin which allows the pin to turn both in the piston and con rod. They can be assembled without tools but have issues if the locks come loose

 

[Scott Danforth]

Ted,

you motor has pressed in pins (most do)

the rod end is generally lightly heated and the wrist pin is pressed thru the piston thru the rod and centered. the wear surface is the piston

Full-Floating rods have bushings and floating pins. the pins are held into the pistons by dual spiral lock (smalley) rings

if you want full-floating and have pressed pins now, buy new rods, its about $850 in labor to get a set of rods condition and bushed for full floating rods, and a set of forged H-beam rods is about $450

 

[Rick Stephens]

if you want full-floating and have pressed pins now, buy new rods, its about $850 in labor to get a set of rods condition and bushed for full floating rods, and a set of forged H-beam rods is about $450

Yikes! My wallet would feel that.

 

[alldodge]

Forgot about semi floating

http://blog.jepistons.com/wrist-pin-locks-different-types-and-how-to-install-them

 

[tpenfield]

Ted,

you motor has pressed in pins (most do)

the rod end is generally lightly heated and the wrist pin is pressed thru the piston thru the rod and centered. the wear surface is the piston

Full-Floating rods have bushings and floating pins. the pins are held into the pistons by dual spiral lock (smalley) rings

if you want full-floating and have pressed pins now, buy new rods, its about $850 in labor to get a set of rods condition and bushed for full floating rods, and a set of forged H-beam rods is about $450

Not that I want to change the wrist pin setup, I just wanted to understand where the bearing wear will be. Looks like it is the wrist pin ends and the piston that wears. I guess that is why you see new pins and pistons in rebuild kits. So, I guess that is what I will be planning on for the rebuild, is new pistons and wrist pins.

 

[Scott Danforth]

Yikes! My wallet would feel that.

I dang near s#!t when the price came back from the machine shop. spending money on buying new rods was easier after that. Summit matches prices.

 

[tpenfield]

Thanks for the info. It looks like there is a certain amount of technique & tricks for getting the old wrist pins out of the piston/connecting rods and inserting the new pins into the pistons/rods.

I have noticed that some engine rebuild kits come with new connecting rods as well as pistons & pins. Is that to avoid the hassle of taking the old rod/piston assemblies apart? Or are there other reasons to have new connecting rods?

Also, I assume that with the new installation, you would want to get the new wrist pin centered on the connecting rod as much as possible. I've read on some engine rebuilding forums that there are varying views on being off center a bit (0.1"-0.2"), as to it being OK as long as the 'play' in the side-to-side fit allows the connecting rod to come back to center with the piston. Some of these misalignments even being done by a shop rather than a DIY'er. I would still think being off center is less that ideal. Thoughts ?

 

[Scott Danforth]

Thanks for the info. It looks like there is a certain amount of technique & tricks for getting the old wrist pins out of the piston/connecting rods and inserting the new pins into the pistons/rods.

Its called pay the machine shop $40. they have the press, the gauges and have done it about 40x a day for the past 40 years.

 

[alldodge]

Until you say otherwise I'm keeping my comments as a standard rebuild

In most cases if a kit comes with rods, it will be to change from fixed to full floating pins. Being dead center is always best and a couple thousands off will not have a noticeable effect. Getting a set a balanced pistons and not just the lowest priced ones, even though the lowest ones will work

 

[Scott Danforth]

not all rotating kits with rods have floating pins. most Scat sets do, however the sets from Mahle (Perfect Circle) and GM dont.

even with a stock rebuild and balance matched components, I still like to have the rotating assembly balanced. I found that even parts from GM need to be balanced.

my last build had all the pistons within a gram of each other, the rods were balanced within half a gram of each other, and the whole rotating assembly still had 4 hours of balancing.

 

[alldodge]

Agree, but ... you can do a standard rebuild without re-balancing everything

 

[Scott Danforth]

it can be done.

however Im not convinced Ted needs anything other than maybe a valve job if he is keeping it stock. until the heads come off, we are all Tuesday morning quarterbacking from our armchairs.

 

[tpenfield]

I’m just asking questions regarding the tidbits of engine dis-assembly / re-aasmbly that are not clear to me. Not going to really know what the rebuild will entail until the engine is opened up.