1998 Volvo Penta 5.7 GS, Valve Mystery

[Hooked on Deanna]

My 1998 VP 5.7 GS (carb'd) started backfiring throughg the carb last season - first intermittenly then constant. Compression test should zero on cylinder #5. Before tearing it apart my mechanic friend losened the valve and reset the lash - problem solved - ran strong (2 months) until winter storage. This season almost exact time last year I started hearing intermitten back fire. Decide to compression check and all cyliders except #7 was 185. Cylinder #7 was 140 (all plugs out engine was warm). In both cases I grounded out the spark to all cylinders and all but the low compressio cylinders effected the idle.

Today my mechanic friend reset the valve lash and the cylinder came back alive (good compression and effect when spark taken away).

My mechanic is stumped as to why this is happening! I started using sea foam last year and was wondering if intake valve carbon buildup may have been removed causing the valve open conditioin or something????

Any ideas??????

 

[Walt T]

Re: 1998 Volvo Penta 5.7 GS, Valve Mystery

I'd probably use my borescope to see whats going on in the cylinder. 5 and 7 are next to each other so that suggests a head gasket or another problem. Valve lash nearly always changes because of lifters. You may have camshaft and or lifter problems developing. Low oil pressure can do this or incorrect oil. Might try running some lifter cleaner in the oil, we oldtimers used to use ATF in the oil but that was before Vortec roller hydraulic lifters. We'd pour a quart of ATF in the oil, let it run a half hour or so, the change the oil and filter. Would free up lifters pretty good and quiet noisy ones temporarily.

 

[Jason89sunbird]

Re: 1998 Volvo Penta 5.7 GS, Valve Mystery

Sticky valve is usually due to sludge under the valve cover. Was there a lot when he first did a valve adjust? I would run one quart of ATF in the oil like Walt said. If that doesn't work pull the heads and rebuild them. I have seen plenty of low mile vortec stick a valve in trucks. I can think of 4 of them and I might have the fifth one in my shop right now

 

[Hooked on Deanna]

Re: 1998 Volvo Penta 5.7 GS, Valve Mystery

Thanks for the feedback!

The oil look great under the valve cover. I've own the boat for two seasons after it sat for over 5 years - yes 5 years on a dealers lot. Short of the noted issue she runs strong! I use 30 weight Castro GTX and change twice a year. Purchased with 450 hrs and i've added 100 hrs. I had other suggest small water leak also...Iwill run rest of the season and check compression. Cylinder 5 acted up last year and is good now. I'm thinking hard about rebuilding head but what a waste of money if she is "fixed"...