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Cam belt failure engine damage?
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SebW20




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1998 Toyota MR2 Mk2 NA Rev5

PostPosted: Sun Jul 23, 2017 6:38 pm    Post subject: Cam belt failure engine damage? Reply with quote Reply with quote including images

Rev5 UK NA

Hi guys, recently had a cam belt failure caused by a seized water pump. Had the engine out and replaced all the necessaries. The engine is now back in and ready to be started again, however it doesn't' want to know.

Getting 6 bar compression on each of the cylinders, which is low but odd that it's consistent across all 4.

I'd been working under the premise that the 3SGE is a non-interference engine but does this sound like engine damage?

Anyone else had a cam belt failure with the engine running? Was there damage?

Cheers!
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jon
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1994 Toyota MR2 Mk2 Turbo Rev3

PostPosted: Sun Jul 23, 2017 8:02 pm    Post subject: Reply with quote Reply with quote including images

I've had a cam belt failure on a V6 3VZ-FE, same as you water sump seized. No damage but getting the crank and cams all lined up was a pain.

It sounds like you've got the cam timing wrong if all cylinders have low compression. Did you check for TDC on cylinder 1? You could be 180 degrees out as crank turns twice for one rotation of the camshaft.
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pbmr2
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PostPosted: Thu Jul 27, 2017 1:13 pm    Post subject: Reply with quote Reply with quote including images

had a belt go at 7k rpm, no problem other than a new cambelt kit. change the water pump while you are at it and the tensioner.
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Draven




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PostPosted: Thu Jul 27, 2017 1:36 pm    Post subject: Reply with quote Reply with quote including images

I'm guessing you can turn the engine over by hand?

It is non interference so the pistons shouldn't have hit the valves.

You sure you've plumbed it back in properly.
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pbmr2
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PostPosted: Fri Aug 04, 2017 8:27 pm    Post subject: Reply with quote Reply with quote including images

yeah sounds like a timing error. best double check that!

If TDC is hard to find for whatever reason, you can varify by sticking the dip stick down cylinder 1 spark plug hole. the cams you can see with the cam cover off and/or line up the markings on the pullies to the back cover.

good luck!
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gips




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PostPosted: Tue Aug 15, 2017 7:49 am    Post subject: Reply with quote Reply with quote including images

Valves are hit and they don't seal properly. The engine will hit them if belt is snapped unless maybe ,if it snaps during cranking. Have seen 3 engines with snapped belts, all had the same problem. You need new valves. I think the bearings should be fine, but you can replace them just in case.
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Draven




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PostPosted: Tue Aug 15, 2017 8:14 am    Post subject: Reply with quote Reply with quote including images

gips wrote:
Valves are hit and they don't seal properly. The engine will hit them if belt is snapped unless maybe ,if it snaps during cranking. Have seen 3 engines with snapped belts, all had the same problem. You need new valves. I think the bearings should be fine, but you can replace them just in case.


The 3S engines are non-interference. So if the belt snaps the pistons will not hit the valves.

So nothing should be damaged from the cam belt snapping.
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gips




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PostPosted: Tue Aug 15, 2017 8:40 am    Post subject: Reply with quote Reply with quote including images

[Smile] He will be back and you will see the result. They do hit valves believe me, no matter that its written as non interference.
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Gazza_DJ
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PostPosted: Tue Aug 15, 2017 9:13 am    Post subject: Reply with quote Reply with quote including images

gips wrote:
[Smile] He will be back and you will see the result. They do hit valves believe me, no matter that its written as non interference.


The only way that will happen is if it has non standard cams and / or valves, or there is another failure that has caused the valve to drop.

Given that compression is pretty much equal across all 4 and low, it is most likely a mechanical timing issue as others have said.
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pbmr2
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PostPosted: Tue Aug 15, 2017 9:57 am    Post subject: Reply with quote Reply with quote including images

gips wrote:
[Smile] He will be back and you will see the result. They do hit valves believe me, no matter that its written as non interference.


Had a belt snap at 7000rpm and drove home from the track day. No damage other than a broken belt. that was a rev2 3sge engine.

no valve damage, boroscope when home showed no piston contact with valves.

1st hand experience of the non interference, not interfering [Very Happy]
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tottacrolla




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PostPosted: Tue Aug 15, 2017 11:59 am    Post subject: Reply with quote Reply with quote including images

pbmr2 wrote:
gips wrote:
[Smile] He will be back and you will see the result. They do hit valves believe me, no matter that its written as non interference.


Had a belt snap at 7000rpm and drove home from the track day. No damage other than a broken belt. that was a rev2 3sge engine.

no valve damage, boroscope when home showed no piston contact with valves.

1st hand experience of the non interference, not interfering [Very Happy]


Blimey, impressive.
I've heard of engines running without oil before but this goes a whole stage further !
was it running in EV mode ?
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Gazza_DJ
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PostPosted: Tue Aug 15, 2017 12:13 pm    Post subject: Reply with quote Reply with quote including images

It's non interference, that's what the cut outs on the stock pistons are for. With stock pistons and stock head / valvetrain etc, the valves at their lowest point still won't contact the pistons at the highest point of their travel.
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pbmr2
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PostPosted: Tue Aug 15, 2017 10:41 pm    Post subject: Reply with quote Reply with quote including images

tottacrolla wrote:
pbmr2 wrote:
gips wrote:
[Smile] He will be back and you will see the result. They do hit valves believe me, no matter that its written as non interference.


Had a belt snap at 7000rpm and drove home from the track day. No damage other than a broken belt. that was a rev2 3sge engine.

no valve damage, boroscope when home showed no piston contact with valves.

1st hand experience of the non interference, not interfering [Very Happy]


Blimey, impressive.
I've heard of engines running without oil before but this goes a whole stage further !
was it running in EV mode ?


Was bone stock rev2 engine, just filter and exhaust and about 120000 miles on the clock at the time. 3s bomproofness built in. it ain't no Ford.
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synXero




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PostPosted: Wed Aug 16, 2017 12:29 am    Post subject: Reply with quote Reply with quote including images

pbmr2 wrote:
gips wrote:
[Smile] He will be back and you will see the result. They do hit valves believe me, no matter that its written as non interference.


Had a belt snap at 7000rpm and drove home from the track day. No damage other than a broken belt. that was a rev2 3sge engine.

no valve damage, boroscope when home showed no piston contact with valves.

1st hand experience of the non interference, not interfering [Very Happy]


Forgive me if I misread but how the xxxx did you drive home with no belt?!
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pbmr2
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PostPosted: Wed Aug 16, 2017 8:18 am    Post subject: Reply with quote Reply with quote including images

Well of course it didn't drive with a snapped belt [Laughing]
put another one on at the track, in the pits. didn't have the full belt kit to hand, mate went off and grabbed another belt.

Later found the original cause was failing tensioner, lasted the 90 miles home though. The same engine went on for another 4 years.
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Gazza_DJ
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PostPosted: Wed Aug 16, 2017 9:21 am    Post subject: Reply with quote Reply with quote including images

I'm sure I remember a story on here or MR2OC about someone who fitted a new belt at the roadside as well [Think]
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synXero




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PostPosted: Wed Aug 16, 2017 9:22 am    Post subject: Reply with quote Reply with quote including images

pbmr2 wrote:
Well of course it didn't drive with a snapped belt [Laughing]
put another one on at the track, in the pits. didn't have the full belt kit to hand, mate went off and grabbed another belt.

Later found the original cause was failing tensioner, lasted the 90 miles home though. The same engine went on for another 4 years.


Skillz.
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SebW20




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1998 Toyota MR2 Mk2 NA Rev5

PostPosted: Mon Sep 11, 2017 7:07 pm    Post subject: Reply with quote Reply with quote including images

Sorry for the delayed follow up on this one...! It was indeed a timing error; with this rectified the engine started immediately and no sign of any damage (touch wood!)
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pbmr2
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PostPosted: Mon Sep 11, 2017 8:11 pm    Post subject: Reply with quote Reply with quote including images

knew it would be fine, glad you sorted it [thumleft]
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Driftlimits Performance
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1994 Toyota MR2 Mk2 Turbo Rev3

PostPosted: Tue Sep 12, 2017 11:14 am    Post subject: Reply with quote Reply with quote including images

Indeed, if you had bent valves you would have no compression. Glad you sorted it.
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