Logo
FULL SITE MENU

Mercruiser 2.5 cam shifting horizontally

T

The Aerofish

New member
Recently purchased a 1981 StarCraft with a 2.5 120 hp Mercruiser. The motor had a good knock to it so ended up tearing it down. Cam bearings are exceptionally wore but also noticed the cam “rocking” back and forth. The cylinders all checked out at 160-165 psi. No visible signs of crank or rod bearing wear. Just the cam bearings. Lifters and pushrods all look good visibly, but maybe some minor wear on bottom of lifters. My current plan is to replaced the cam bearings, cam, lifters and pushrods just to rule anything out. Also while I’be got the motor tore down, was going to replace crank and rod bearings as well. Does anyone have any thoughts on what may be going on?
 
It sounds like, due to the severe wear on the cam bearings the distributor is jumping so look close at the distributor gear and cam gear. Thats my guess.

I would also look close at the timing chain/gears depending on what is used in that engine.
 
kghost said:
It sounds like, due to the severe wear on the cam bearings the distributor is jumping so look close at the distributor gear and cam gear. Thats my guess.

I would also look close at the timing chain/gears depending on what is used in that engine.
Click to expand...
Thanks for the response. Interesting thing is the cam gear (no chain, gear driven) and crank gear are both clean with no odd wear. Same with the distributor gear and gear on the cam . I have some pictures I can post. Seems I’m having an issue with that though not sure if there is a minimum post number before I can upload photos like some forums.
 
The Aerofish said:
Thanks for the response. Interesting thing is the cam gear (no chain, gear driven) and crank gear are both clean with no odd wear. Same with the distributor gear and gear on the cam . I have some pictures I can post. Seems I’m having an issue with that though not sure if there is a minimum post number before I can upload photos like some forums.
Click to expand...
Its typically the size of the image file.
If you use a camera the saved file is very large.

Not sure you know how to shrink the file size or not
 
The Aerofish said:
Thanks for the response. Interesting thing is the cam gear (no chain, gear driven) and crank gear are both clean with no odd wear. Same with the distributor gear and gear on the cam . I have some pictures I can post. Seems I’m having an issue with that though not sure if there is a minimum post number before I can upload photos like some forums.
Click to expand...
If the image size is the problem and they're saved to your desktop or in a folder, hover the cursor over the file and right click on 'Open With'- if you use Windows, you should see an option to use Microsoft Paint. Select that one and when it opens, you should see the option to resize at the upper left. If you see boxes for selecting 'Rulers', 'Gridlines' and 'Status Bar', you'll see two buttons called Home and View- click on Home and you'll see the Resize button. Left click on that button and look for the black dot- it comes up as 'Percentage' with the option for Pixels- click on Pixels and if it shows the image size as more than 1000, reduce it to about 600 on the upper box. You can use backspace to change this if the cursor is at the left of the first digit or Delete if the cursor is on the right of the last digit. Save and rename the photo-I usually add 'For Web' at the end, to make it easy to pick that one.
 
IMG_7154.jpeg
IMG_7149.jpeg
IMG_7148.jpeg
 
The Aerofish said:
I thought of that. Someone was in the block prior. The rear freeze plug had RTV around the rim of it. I wonder if someone tried pressing them in on their own.
Click to expand...
It is not unusual to use something like permatex #3 on the freeze plugs especially if the bore is rough.

Cam bearings require a install tool. is there a core plug in end of block that is allowing freeplay in cam. I think most flat tappet cams can move a bit , just not as much as yours is. Would check that what ever holds the cam in the block was correctly installed bend the timing gear
 
I am wondering if the cam shaft may be bent/warped?

Look at timing gear cover, see any wear on it from cam gear?
 
Dieter said:
It is not unusual to use something like permatex #3 on the freeze plugs especially if the bore is rough.

Cam bearings require an install tool. is there a core plug in end of block that is allowing freeplay in cam. I think most flat tappet cams can move a bit , just not as much as yours is. Would check that what ever holds the cam in the block was correctly installed bend the timing gear
Click to expand...
Yes that was my initial thought before pulling the cam, perhaps the thrust washer wasn’t installed. But upon pulling it out, I can see the washer behind the thrust plate. There is a core plug that I’m assuming the cam end sits against, it seems to me is properly placed. Something is haywire and at the most extreme I’m thinking bent cam? I’d love to save the cam if possible, I see some wear on lobes but nothing I would think detrimental. Was going to take the block and cam to the machine shop and spec the cam, and install new cam bearings.
 
Next, check distibutor shaft bushings for out of round, it is common on angle inatalled distributors to have the bushing wear. This may explain the movement of the cam shaft weird movement.
Also I am not sure how the fuel pump is pulsed, does it use a dedicated cam lobe like the SBC? If so that may be causing the weird movement.
But the fact that the cam bearings are so worn almost any pressure on the shaft will cause that movement.
 
kghost said:
Next, check distibutor shaft bushings for out of round, it is common on angle inatalled distributors to have the bushing wear. This may explain the movement of the cam shaft weird movement.
Also I am not sure how the fuel pump is pulsed, does it use a dedicated cam lobe like the SBC? If so that may be causing the weird movement.
But the fact that the cam bearings are so worn almost any pressure on the shaft will cause that movement.
Click to expand...
Ok, wasn’t aware of bushings along the distributor shaft. The fuel pump does use a dedicated lobe. Maybe a sign too, the fuel pump looks to be very recently replaced. I added a short clip of the motor idling and at mid range rpms. Can only imagine the walking of the cam as in the video rotating by hand is definitely amplified at running RPMs. Couldn’t exactly place the knock but definitely sounded up front at the pulleys.
https://youtube.com/shorts/xyLcpUrnBjA?si=UaDv-9B7f9EmAa31
 
I finished up with work for the day and looked over the distributor shaft. I do see some wear and tear along the shaft and looks the same at the area the shaft drops in through the block. Is this because of the bad bushing the lower part of the shaft fits through? I can get a slight rocking dropping the distributor into the slot. I see the bushing is replaceable. Is the wear on the block a concern? Would this alone cause enough play to allow the cam to shift? Also some photos of the cam lobes, and cam gear.
img_7338-jpeg.32455
img_7336-jpeg.32456
IMG_7339.jpeg
IMG_7345.jpeg
IMG_7343.jpeg
IMG_7344.jpeg
 

Attachments

  • IMG_7338.jpeg
    IMG_7338.jpeg
    48.1 KB · Views: 23
  • IMG_7336.jpeg
    IMG_7336.jpeg
    42.3 KB · Views: 22
The outside diameter doesnt move once timing is set so any wear should not impact anything.
If the wear on the bushing that is worn doesnt seem to impact point set up then you may be OK.
There are two bushings, one under point plate and one near gear side inside housing. Oil light type bushings.
If the one under point plate is worn the shaft will move side to side making setting point gap/dwell difficult.

I have seen them so worn the points once set would close when on the rong side of the wobble and cause bad running conditions as the dwell was all over the place thus timing was also.
 
Ok, I’ll take a peek beneath the cap. I feel it’s likely the cam bearings being the way they are is where my knock has came from, but trying to figure out where and why they went bad. As one mentioned, looks like they may have been improperly installed. Hoping I have caught this early on because otherwise the motor seems to be pretty good overall condition besides the current issie
 
I will be dropping the block, cam, and crank off at the machine shop Tuesday. I have the cam bearings delivered and going to have them pressed in. Also, for sure the engine block distributor bushing has some pretty good wear to it. I’m going to have them check the crank and rod journals to be sure they are not out of round. Also going to have them remove the cam timing gear and inspect the thrust plate and washer. The current plan if all checks out is to replace the cam with new if bad, new lifters and pushrods, crank and rod bearings while I’m in it.
 
Back
Top