Piston slap anyone??
Posting Guru
Joined: Mar 2004
Posts: 1,099
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From: Destin/Ft. Walton Beach,
It's pretty simple to tell if you have a bad rod bearing, and if you have an oil pressure gauge. When you rev an engine with a bad rod bearing, the oil pressure goes down instead of up, because of centrifugal force causing the oil to sling out through the large bearing clearance. Many 302 engines develop a piston slap, but they usually run for a long time afterwards. The late 70's and early 80's were the worst for this. I couldn't tell you how many of these engines I've pulled the pan on, only to find piston skirt peices.
New User
Joined: May 2004
Posts: 9
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RTM and others,
You have confirmed what everyone wanting my money has said. Replace the motor! Replace ther Rod bearing and it is just a banaid. Well, she is now parked and I will be ordering a motor. Any recomendations on a replacement brand or supplier? Grooms Jeggs.... I am thinking long block to make it easy on a first timer. Easy yeah right
You have confirmed what everyone wanting my money has said. Replace the motor! Replace ther Rod bearing and it is just a banaid. Well, she is now parked and I will be ordering a motor. Any recomendations on a replacement brand or supplier? Grooms Jeggs.... I am thinking long block to make it easy on a first timer. Easy yeah right
New User
Joined: May 2004
Posts: 9
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Cold Start 3-4 Distict Knocks. Assuming the journals/bearing fills up with oil. Knock stops.
Warm or cold free rev to 1800 knock constanly.
Warm or cold hard acceleration knocking at 2500>
Once warmed up and idleing I can hear the knock very faint.
It is not injectors or lifters. I can hear all three.
Warm or cold free rev to 1800 knock constanly.
Warm or cold hard acceleration knocking at 2500>
Once warmed up and idleing I can hear the knock very faint.
It is not injectors or lifters. I can hear all three.
Junior User
Joined: Apr 2004
Posts: 80
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From: west virginia
you might not believe this but i had a 86 merc with a 302 and it had a knock when it first started and would go away as it got warm. but 1 thing I found out was the oil filter i was using did not have a 1 way check valve made in it I guess that is what you call it but I went to better filter and it had 1 and it kept the oil up in the motor and it made a big difference
Posting Guru
Joined: Apr 2003
Posts: 1,456
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From: Indiana
Find the cylinder in question and pull the spark plug wire if the knock goes away its more than likely the rod bearing. If not its probaly piston slap. In my opion mains sound completly different not as solid of a knock.
Elder User
Joined: Sep 2003
Posts: 908
Likes: 4
"you might not believe this but i had a 86 merc with a 302 and it had a knock when it first started and would go away as it got warm. but 1 thing I found out was the oil filter i was using did not have a 1 way check valve made in it I guess that is what you call it but I went to better filter and it had 1 and it kept the oil up in the motor and it made a big difference"
Yep, that's the piece of crap Fram. I wonder how many engines with bad main bearings are because of the "orange can of death."
NEVER EVER EVER EVER use a Fram filter!!!!!! They empty out overnight, and while your oil pump is refilling it, the bearings are starving for oil.
Don't take my word for it. Look at this:
http://www.scuderiaciriani.com/rx7/oil_filter_study/
The $2.50 Walmart Motorcraft filter is one of the best. Use it.
Yep, that's the piece of crap Fram. I wonder how many engines with bad main bearings are because of the "orange can of death."
NEVER EVER EVER EVER use a Fram filter!!!!!! They empty out overnight, and while your oil pump is refilling it, the bearings are starving for oil.
Don't take my word for it. Look at this:
http://www.scuderiaciriani.com/rx7/oil_filter_study/
The $2.50 Walmart Motorcraft filter is one of the best. Use it.
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Junior User
Joined: May 2002
Posts: 52
Likes: 0
From: anchorage
am pulling the motor the heads areoff saturday night and block is comeing out this morning . will tell you what i found. so far i see there are deep four brow pistons ,i had the do0e heads with big valves.
Junior User
Joined: May 2002
Posts: 52
Likes: 0
From: anchorage
well found the problem rod# 2 bearing all the way down to the steel backing and grooved looking at the rest of the bearing copper still there but defennatly tired its a 10-10 crank and rod and 30 over on the piston. but the funny thing ot even 40 weight oil sould shut the bearing up oh well new bearing friday and oil pump and call it good thanks everyone
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Nov 27, 2005 03:51 PM